A method for optimizing frequency modulation parameters of a conventional direct current transmission system

Abstract

The application discloses a frequency modulation parameter optimization method of a conventional direct current transmission system, and belongs to the technical field of frequency modulation control of power systems. The frequency modulation parameter optimization method of the conventional direct current transmission system comprises the following steps: parameters of each synchronous generator in a receiving-end power grid are counted, a frequency response model of a receiving-end system on an inverter side is established and is differentially dispersed; according to a frequency variation of the receiving-end power grid, an increase of an instruction value of a fixed active power control on a rectifier side is calculated, and the increase is taken as an active power disturbance of a sending-end new energy base; the sending-end new energy base on the rectifier side responds to the active power disturbance through primary frequency modulation and virtual inertia control; a frequency modulation parameter optimization model is established; and a commercial solver is called to solve the frequency modulation parameter optimization model. The frequency modulation parameter optimization method of the conventional direct current transmission system supports the frequency of the receiving-end power grid, guarantees the stability of the frequency of the sending end, improves the frequency support level of the new energy station to the power grid, and ensures the safety of power system operation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system frequency modulation control, and particularly relates to a frequency modulation parameter optimization method for a conventional HVDC system. BACKGROUND

[0002] With a large-scale access of high-proportion new energy to the power system, the inertia support capability of the power grid is reduced, and the system frequency stability is facing severe challenges. As the backbone network of cross-regional power transmission, the high-voltage direct current (HVDC) transmission system has the ability of fast power regulation, which is regarded as an important means to provide emergency frequency support and enhance system stability. The conventional HVDC system (based on grid commutated converter, LCC-HVDC) is usually configured with a frequency limit controller (FLC) or similar frequency coordination control function, so that it can provide fast frequency support for the sending or receiving end AC system when the AC system frequency deviates significantly.

[0003] However, the existing conventional DC system has significant limitations in participating in frequency support control: on the one hand, its regulation strategy only responds to local signals, i.e. it uses a one-way control strategy, and does not coordinate the dynamic interaction of the opposite end, which may cause a reverse power impact on the frequency stability of the opposite end while ensuring the frequency of one end; on the other hand, if the parameters are not properly set, it may cause excessive interaction between the DC power and the AC system frequency, and even lead to power oscillation, which threatens the safe and stable operation of the system. Especially in the context of new power systems, the operating characteristics of the power grid are more complex and variable, and the traditional fixed parameter strategy is difficult to adapt to the optimal frequency support requirements in all operating conditions and all scenarios. SUMMARY

[0004] The purpose of the present application is to provide a frequency modulation parameter optimization method for a conventional HVDC system, which realizes the calculation of related frequency modulation parameters of the sending end new energy base and the conventional HVDC system, supports the frequency of the receiving end power grid, ensures the stability of the frequency of the sending end, improves the frequency support level of the new energy station to the power grid, and ensures the safety of the operation of the power system.

[0005] To achieve the above purpose, the present application provides a frequency modulation parameter optimization method for a conventional HVDC system, comprising the following steps:

[0006] S1, the parameters of each synchronous generator in the receiving end power grid are counted, the frequency support capability of each synchronous generator in the receiving end power grid is determined, an inverter side receiving end system frequency response model is established and is differentially dispersed;

[0007] S2. Based on the frequency change of the receiving-end grid in the receiving-end system frequency response model, calculate the increase in the command value of the constant active power control on the rectifier side, and transmit the increase in the command value to the rectifier side as the active power disturbance of the sending-end new energy base on the rectifier side.

[0008] S3. The rectifier-side power supply base responds to the active power disturbance through primary frequency regulation and virtual inertia control, increasing power generation to support the receiving-end grid frequency.

[0009] S4. Establish a frequency modulation parameter optimization model;

[0010] S5. Call a commercial solver to solve the frequency regulation parameter optimization model and obtain the frequency regulation parameter optimization results of the conventional DC transmission system.

[0011] Preferably, in step S1, the parameters of the synchronous generator include the inertial time constant H, the droop coefficient R, and the rated capacity S. n High-pressure cylinder power ratio F HP Reheater time constant T RH Generator kinetic energy, speed deviation amplification factor K.

[0012] Preferably, in step S1, the specific process of establishing the frequency response model of the inverter-side receiver system and performing differential discretization includes:

[0013] S11. Equivalently aggregate different synchronous generators at the receiving end into a single equivalent synchronous machine;

[0014] S12. Calculate the equivalent inertial time constant H at the receiving end of the equivalent synchronizer. eq2 The equivalent adjustment coefficient R at the receiving end eq2 The time constant T of the reheater at the receiving end RH2 The power ratio F of the high-pressure cylinder at the receiving end HP2 ;

[0015]

[0016] Among them, S N2 H is the rated capacity of the receiving-end system. i Let S be the inertial time constant of the i-th synchronous generator. i Let K be the rated capacity of the i-th synchronous generator at the receiving end, r be the number of synchronous generators, and K be the number of synchronous generators. mi R represents the ratio of the capacity of the i-th synchronous generator to the rated capacity of the receiving-end system. i Let be the droop coefficient of the i-th synchronous generator. Denotes the reheater time constant of the i-th synchronous generator. The high-voltage cylinder power ratio of the i-th synchronous generator;

[0017] S13. Establish a frequency response model of the receiving-end system after grid disturbance based on the rotor motion equation and perform differential discretization.

[0018] The frequency response model of the receiving-end system is:

[0019]

[0020] Where f0 is the rated frequency, Δf2 is the receiving-end frequency deviation, H2 is the equivalent inertial time constant of the receiving-end synchronous generator, D is the damping coefficient, and ΔP G2 ΔP represents the change in primary frequency modulation power of the equivalent synchronous machine at the receiving end. m1 ΔP is the sum of the power changes of the frequency regulation units in the sending-end new energy base. L The active power change is the change in load, and t is time.

[0021] The difference form of the difference discretization process is:

[0022]

[0023] Where, Δf 2,n For ΔP to occur L The frequency deviation at the nth step size of the receiving end when the disturbance is large, d n The difference step size;

[0024] The differential form of the change in the primary frequency regulation power of the equivalent synchronous machine after the power grid disturbance at the receiving end is as follows:

[0025]

[0026] Wherein, ΔP G2,n This refers to the additional active power generated by the receiving-end equivalent synchronous machine at the nth step size. These represent the active power adjustment of the receiving-end synchronous generator after the dead zone and speed governor limiting at the nth step size. For the primary frequency regulation dead zone of the receiving-end synchronous generator, R G2 This is the active power reserve value of the receiving-end synchronous generator.

[0027] Preferably, in S2, the differential form of the increase in the command value of the rectifier-side constant active power control is:

[0028]

[0029] in, The per-unit value representing the increment of the active power control command value at the nth step size on the rectifier side. These represent the power increment of the LCC-HVDC transmission line after passing through the dead zone and limiting zone at the nth step. T is the theoretical value of the power transmission increment of the LCC-HVDC line in the nth step. DCR is the time constant for additional frequency control. HVDC This refers to the transmission limit power of the LCC-HVDC line. The dead zone for instruction calculation, K dc H dc This is the gain coefficient. Rated transmission power for LCC-HVDC systems.

[0030] Preferably, in step S3, the rectifier-side power transmission base responds to the active power disturbance through primary frequency regulation and virtual inertia control, specifically as follows:

[0031] Based on the increase in the active power command value on the rectifier side, the frequency dynamic response process of the sending-end new energy base is characterized by the rotor motion equation, and differential analysis is performed. The differential form is as follows:

[0032]

[0033] Where, Δf 1,n H represents the frequency deviation of the nth step size at the sending end. eq1 S is the equivalent inertial time constant of the sending-end synchronous generator. N1 ΔP is the rated capacity of the sending-end system. m1,n-1 This represents the power change of the frequency regulation unit at the sending-end new energy base at the (n-1)th step.

[0034] Preferably, in S3, the increased power generation includes the primary frequency regulation increased power generation of the synchronous generator in the sending-end new energy base, the droop control increased power generation of the wind turbine, the droop control increased power generation of the photovoltaic power generation unit, and the droop control increased power generation of the energy storage unit.

[0035] The differential form of the primary frequency regulation power increase of a synchronous generator is as follows:

[0036]

[0037] Wherein, ΔP G1,n This refers to the additional active power generated by the equivalent synchronous machine at the sending end during the nth step. These represent the active power adjustment of the sending-end synchronous generator after the dead zone and speed governor limiting at the nth step size. For the primary frequency regulation dead zone of the sending-end synchronous generator, R G1 R is the active power reserve value of the sending-end synchronous generator. eq1 T is the equivalent droop factor at the sending end. RH1 F is the time constant of the feed-end reheater. HP1 The power ratio of the high-pressure cylinder at the sending end. The rated power of the sending-end synchronous machine; the differential form of the wind turbine droop control power generation is:

[0038]

[0039] Wherein, ΔP w1,n This refers to the additional active power generated by the sending-end wind turbine at the nth step. These represent the active power adjustment of the sending-end wind turbine unit after the nth step size, including dead zone and limiting. For the primary frequency regulation dead zone of the sending-end wind turbine, R w1 To reserve power for the sending-end wind turbine units, T w1 The time constant of the sending-end wind turbine inverter. The sending end is the rated power of the wind turbine, K w1 This is the equivalent droop coefficient for the fan;

[0040] The differential form of the increased power generation due to droop control of photovoltaic power generation units is as follows:

[0041]

[0042] Wherein, ΔP pv1,n This refers to the additional active power generated by the sending-end photovoltaic power generation unit at the nth step. These represent the active power adjustment of the nth step size of the sending-end photovoltaic power generation unit after dead zone and limiting. For the primary frequency regulation dead zone of the sending-end photovoltaic power generation unit, R pv1 To reserve power for the sending-end photovoltaic power generation unit, T pv1 The time constant of the inverter in the sending-end photovoltaic power generation unit. K represents the rated power of the sending-end photovoltaic power generation unit. pv1 This is the photovoltaic equivalent droop factor;

[0043] The differential form of the power generation increase controlled by the droop control of the energy storage unit is as follows:

[0044]

[0045] in, ΔP is the per-unit value of the additional active power generated by the sending-end energy storage unit at the nth step. ess1,n This refers to the additional active power generated by the sending-end energy storage unit at the nth step. These represent the active power adjustment of the sending-end energy storage unit after the dead zone and limiting at the nth step size. For the primary frequency regulation dead zone of the sending-end energy storage unit, R ess1 To reserve power for the sending-end energy storage unit, T ess1 H is the time constant of the inverter in the sending-end energy storage unit. ess1 K is the equivalent inertial time constant for energy storage. ess1 This is the energy storage equivalent droop coefficient. This is the rated power of the sending-end energy storage unit.

[0046] Preferably, in step S4, establishing the frequency modulation parameter optimization model includes the following steps:

[0047] S41. With the goal of minimizing the active power reserve of renewable energy in the sending-end renewable energy base, establish the objective function of the optimization model. The objective function is:

[0048] min{a G1 R G1 +a w1 R w1 +a pv1 R pv1 +a ess1 R ess1};

[0049] Among them, a G1 a w1 a pv1 a ess1 Cost coefficients are reserved for frequency regulation backups for the sending-end synchronous machine, wind turbine, photovoltaic power generation unit, and energy storage unit, respectively.

[0050] S42. Based on the frequency stability requirements of the power system, establish the constraints of the optimization model.

[0051] Preferably, in step S42, the constraint establishment includes the following steps:

[0052] S421. Establish constraints for the active power reserve of frequency regulation units during the frequency support process of the sending-end new energy base:

[0053]

[0054] Among them, b G1 b w1 b pv1 b ess1 These are the pre-set active power reserves of new energy synchronous generators, wind turbines, photovoltaic power generation units, and energy storage units, respectively, relative to their rated power.

[0055] S422. Based on the power system frequency stability guidelines, establish stability constraints for the lowest frequency points of the sending-end and receiving-end systems after disturbances:

[0056]

[0057] in, This indicates the minimum limit of the sending-end base frequency. This indicates the minimum frequency limit of the receiving system.

[0058] Preferably, the frequency regulation parameters of the conventional DC transmission system include sending-end system parameters and conventional DC transmission system parameters;

[0059] The parameters of the sending-end system include: the equivalent droop coefficient K of the fan. w1 Photovoltaic equivalent droop coefficient K pv1 Energy storage equivalent droop coefficient K ess1 Energy storage equivalent inertial time constant H ess1 Reserved power capacity for thermal power plants (R) G1 Reserved power capacity for wind turbine units R w1 Photovoltaic power generation unit reserved power reserve R pv1 The energy storage unit has reserved power for backup. ess1 ;

[0060] Parameters of a conventional DC transmission system include: frequency modulation gain coefficient K. dc H dc .

[0061] The advantages and positive effects of the frequency regulation parameter optimization method for a conventional DC transmission system described in this invention are: This invention realizes the calculation of relevant frequency regulation parameters of the sending-end renewable energy base and the conventional DC transmission system, which is used to support the frequency of the receiving-end power grid, while ensuring the stability of the sending-end frequency, improving the frequency support level of renewable energy bases for the power grid, and ensuring the safety of power system operation.

[0062] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0063] Figure 1 This is a flowchart of the frequency modulation parameter optimization method of the present invention;

[0064] Figure 2 This is a schematic diagram of the system topology used in an embodiment of the present invention;

[0065] Figure 3 This is a schematic diagram of the base frequency results at the sending end in an embodiment of the present invention;

[0066] Figure 4 This is a schematic diagram of the receiving-end power grid frequency results according to an embodiment of the present invention. Detailed Implementation

[0067] In this application, 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 application pertains. In case of any inconsistency, the meaning set forth in this specification or derived from the content described herein shall prevail. Furthermore, the terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit the scope of this application.

[0068] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0069] like Figure 1As shown, a method for optimizing frequency regulation parameters in a conventional DC transmission system includes the following steps:

[0070] S1. Statistically analyze the parameters of each synchronous generator in the receiving-end power grid, determine the frequency support capability of each synchronous generator in the receiving-end power grid, establish the frequency response model of the inverter-side receiving-end system, and perform differential discretization.

[0071] The parameters of a synchronous generator include inertial time constant H, droop coefficient R, and rated capacity S. n High-pressure cylinder power ratio F HP Reheater time constant T RH Generator kinetic energy, speed deviation amplification factor K.

[0072] The specific process of establishing the frequency response model of the inverter-side receiver system and performing differential discretization includes:

[0073] S11. Equivalently aggregate different synchronous generators at the receiving end into a single equivalent synchronous machine.

[0074] Synchronous generator equivalent aggregation is based on the equivalent parameter aggregation method of capacity weighted average. By weighting the key parameters according to the rated capacity ratio of the unit, the characteristics of multiple synchronous generators are equivalent to a single synchronous generator.

[0075] S12. Calculate the equivalent inertial time constant H at the receiving end of the equivalent synchronizer. eq2 Equivalent adjustment coefficient R at the receiving end eq2 The time constant T of the reheater at the receiving end RH2 The power ratio F of the high-pressure cylinder at the receiving end HP2 .

[0076]

[0077] Among them, S N2 H is the rated capacity of the receiving-end system. i Let S be the inertial time constant of the i-th synchronous generator. i Let K be the rated capacity of the i-th synchronous generator at the receiving end, r be the number of synchronous generators, and K be the number of synchronous generators. mi R represents the ratio of the capacity of the i-th synchronous generator to the rated capacity of the receiving-end system. i Let be the droop coefficient of the i-th synchronous generator. Denotes the reheater time constant of the i-th synchronous generator. The high-voltage cylinder power ratio of the i-th synchronous generator;

[0078] S13. Establish a frequency response model of the receiving-end system after grid disturbance based on the rotor motion equation and perform differential discretization.

[0079] The frequency response model of the receiving-end system is:

[0080]

[0081] Where f0 is the rated frequency, Δf2 is the receiving-end frequency deviation, H2 is the equivalent inertial time constant of the receiving-end synchronous generator, D is the damping coefficient, and ΔP G2 ΔP represents the change in primary frequency modulation power of the equivalent synchronous machine at the receiving end. m1 ΔP is the sum of the power changes of the frequency regulation units in the sending-end new energy base. L Let t be the change in active power of the load, and t be time.

[0082] The difference form of the difference discretization process is:

[0083]

[0084] Where, Δf 2,n For ΔP to occur L The frequency deviation at the nth step size of the receiving end when the disturbance is large, d n This is the difference step size.

[0085] The differential form of the change in the primary frequency regulation power of the equivalent synchronous machine after the power grid disturbance at the receiving end is as follows:

[0086]

[0087] Wherein, ΔP G2,n This refers to the additional active power generated by the receiving-end equivalent synchronous machine at the nth step size. These represent the active power adjustment of the receiving-end synchronous generator after the dead zone and speed governor limiting at the nth step size. For the primary frequency regulation dead zone of the receiving-end synchronous generator, R G2 This is the active power reserve value of the receiving-end synchronous generator.

[0088] S2. Based on the frequency change of the receiving-end grid in the receiving-end system frequency response model, calculate the increase in the command value of the constant active power control on the rectifier side, and transmit the increase in the command value to the rectifier side as the active power disturbance of the sending-end new energy base on the rectifier side.

[0089] If the frequency of the inverter-side receiving-end grid changes abruptly in any way, the differential form of the increase in the command value for constant active power control on the rectifier side is:

[0090]

[0091] in, The per-unit value representing the increment of the active power control command value at the nth step size on the rectifier side. These represent the power increment of the LCC-HVDC transmission line after passing through the dead zone and limiting zone at the nth step. T is the theoretical value of the power transmission increment of the LCC-HVDC line in the nth step. DC R is the time constant for additional frequency control. HVDC This refers to the transmission limit power of the LCC-HVDC line. The dead zone for instruction calculation, K dc H dc This is the gain coefficient. Rated transmission power for LCC-HVDC systems.

[0092] S3. The rectifier-side power supply base responds to the active power disturbance through primary frequency regulation and virtual inertia control, increasing power generation to support the receiving-end grid frequency.

[0093] The rectifier-side power transmission base responds to the active power disturbance through primary frequency regulation and virtual inertia control, specifically as follows:

[0094] Based on the increase in the active power command value on the rectifier side, the frequency dynamic response process of the sending-end new energy base is characterized by the rotor motion equation, and differential analysis is performed. The differential form is as follows:

[0095]

[0096] Where, Δf 1,n H represents the frequency deviation of the nth step size at the sending end. eq1 S is the equivalent inertial time constant of the sending-end synchronous generator. N1 ΔP is the rated capacity of the sending-end system. m1,n-1 This represents the (n-1)th step power change of the frequency regulation unit at the sending-end new energy base.

[0097] The increased power generation includes the primary frequency regulation power generation of synchronous generators in the sending-end new energy base, the droop control power generation of wind turbines, the droop control power generation of photovoltaic power generation units, and the droop control power generation of energy storage units.

[0098] The differential form of the primary frequency regulation power increase of a synchronous generator is as follows:

[0099]

[0100] Wherein, ΔP G1,n This refers to the additional active power generated by the equivalent synchronous machine at the sending end during the nth step. These represent the active power adjustment of the sending-end synchronous generator after the dead zone and speed governor limiting at the nth step size. For the primary frequency regulation dead zone of the sending-end synchronous generator, R G1 R is the active power reserve value of the sending-end synchronous generator. eq1 T is the equivalent droop factor at the sending end. RH1 F is the time constant of the feed-end reheater.HP1 The power ratio of the high-pressure cylinder at the sending end. This is the rated power of the sending-end synchronizing machine.

[0101] The differential form of the power generation increase through wind turbine droop control is as follows:

[0102]

[0103] Wherein, ΔP w1,n This refers to the additional active power generated by the sending-end wind turbine at the nth step. These represent the active power adjustment of the sending-end wind turbine unit after the nth step size, including dead zone and limiting. For the primary frequency regulation dead zone of the sending-end wind turbine, R w1 To reserve power for the sending-end wind turbine units, T w1 The time constant of the sending-end wind turbine inverter. K represents the rated power of the wind turbine generator at the sending end. w1 This is the equivalent droop coefficient of the wind turbine.

[0104] The differential form of the increased power generation due to droop control of photovoltaic power generation units is as follows:

[0105]

[0106] Wherein, ΔP pv1,n This refers to the additional active power generated by the sending-end photovoltaic power generation unit at the nth step. These represent the active power adjustment of the nth step size of the sending-end photovoltaic power generation unit after dead zone and limiting. For the primary frequency regulation dead zone of the sending-end photovoltaic power generation unit, R pv1 To reserve power for the sending-end photovoltaic power generation unit, T pv1 The time constant of the inverter in the sending-end photovoltaic power generation unit. K represents the rated capacity of the sending-end photovoltaic power generation unit. pv1 This is the photovoltaic equivalent droop coefficient.

[0107] The differential form of the power generation increase controlled by the droop control of the energy storage unit is as follows:

[0108]

[0109] in, ΔP is the per-unit value of the additional active power generated by the sending-end energy storage unit at the nth step. ess1,n This refers to the additional active power generated by the sending-end energy storage unit at the nth step. These represent the active power adjustment of the sending-end energy storage unit after the dead zone and speed governor limiting at the nth step size. For the primary frequency regulation dead zone of the sending-end energy storage unit, R ess1To reserve power for the sending-end energy storage unit, T ess1 H is the time constant of the reheater in the sending-end energy storage unit. ess1 K is the equivalent inertial time constant for energy storage. ess1 This is the energy storage equivalent droop coefficient. This is the rated power of the sending-end energy storage unit.

[0110] S4. Establish a frequency modulation parameter optimization model.

[0111] Establishing a frequency modulation parameter optimization model includes the following steps:

[0112] S41. With the goal of minimizing the active power reserve of renewable energy in the sending-end renewable energy base, establish the objective function of the optimization model. The objective function is:

[0113] min{a G1 R G1 +a w1 R w1 +a pv1 R pv1 +a ess1 R ess1};

[0114] Among them, a G1 a w1 a pv1 a ess1 The cost coefficients reserved for frequency regulation backups are respectively for the sending-end synchronous machine, wind turbine, photovoltaic power generation unit, and energy storage unit.

[0115] S42. Based on the frequency stability requirements of the power system, establish the constraints of the optimization model.

[0116] Establishing constraints includes the following steps:

[0117] S421. Establish constraints for the active power reserve of frequency regulation units during the frequency support process of the sending-end new energy base:

[0118]

[0119] Among them, b G1 b w1 b pv1 b ess1 These are the pre-set active power reserves of new energy synchronous generators, wind turbines, photovoltaic power generation units, and energy storage units, respectively, relative to their rated power.

[0120] S422. Based on the power system frequency stability guidelines, establish stability constraints for the lowest frequency points of the sending-end and receiving-end systems after disturbances:

[0121]

[0122] in, This indicates the minimum limit of the sending-end base frequency. This indicates the minimum frequency limit of the receiving system.

[0123] S5. Call a commercial solver to solve the frequency regulation parameter optimization model and obtain the frequency regulation parameter optimization results of the conventional DC transmission system.

[0124] Commercial solvers are used to optimize the objective function, calculate the optimal solutions for each variable that satisfy the constraints, and output the calculation results for each difference step size. Finally, the frequency modulation parameters of the sending and receiving end frequency support method based on conventional DC transmission systems are obtained.

[0125] The frequency regulation parameters of a conventional DC transmission system include the sending-end system parameters and the conventional DC transmission system parameters;

[0126] The parameters of the sending-end system include: the equivalent droop coefficient K of the fan. w1 Photovoltaic equivalent droop coefficient K pv1 Energy storage equivalent droop coefficient K ess1 Energy storage equivalent inertial time constant H ess1 Reserved power capacity for thermal power plants (R) G1 Reserved power capacity for wind turbine units R w1 Photovoltaic power generation unit reserved power reserve R pv1 The energy storage unit has reserved power for backup. ess1 ;

[0127] Parameters of a conventional DC transmission system include: frequency modulation gain coefficient K. dc H dc .

[0128] like Figure 2 As shown, frequency regulation parameter optimization calculations are performed based on the sending-end base—conventional DC transmission system—receiving-end power grid system. The operation steps are as follows:

[0129] 1. A load surge of 1720MW is introduced at the receiving end of the power grid, causing the grid frequency to exceed the dead zone of the primary frequency regulation operation of the synchronous motor governor. Analyze the main parameters of each synchronous motor in the power grid, including: inertial time constant H, droop coefficient R, and rated capacity S. n High-pressure cylinder power ratio F HP Reheater time constant T RHThe generator kinetic energy and speed deviation amplification factor K are considered. The synchronous generator units in the improved receiving-end power grid are aggregated into an equivalent synchronous machine. Considering nonlinear elements such as governor dead zone and amplitude limiting, a dynamic characteristic model of the receiving-end system frequency support under the anticipated disturbance is established and differentially discretized to obtain expressions for the frequency deviation of the receiving-end power grid after the disturbance. In this embodiment, the frequency dead zone of the governor of the receiving-end power grid synchronous generator units is set to 0.033Hz, the active power limit is set to 10% of the capacity, and the droop coefficient is set to 0.04.

[0130] 2. Based on the frequency deviation of the receiving-end power grid, calculate the increase in the constant active power control command value on the rectifier side of the conventional DC transmission system, and transmit it to the rectifier side via communication, while also serving as the power disturbance amount at the sending-end base.

[0131] 3. Establish a discretized model of the frequency response of the sending-end base station to obtain discrete expressions for the frequency deviation of the sending-end base station system and the increased active power of each unit. In this embodiment, the differential step size is 0.02s.

[0132] When using a commercial solver for optimization calculations, it is necessary to initialize all variables. In this embodiment, the initial system frequency deviation is 0, and the initial additional active power generated by the equivalent synchronous generator is 0.

[0133] 4. Optimize the frequency regulation parameters of new energy sources. In this embodiment, the active power reserve selection range of each new energy source is set to 15% of the rated power.

[0134] 5. Establish constraints based on system frequency stability requirements, including constraints on active power reserve of new energy sources, maximum system frequency change rate, and maximum system frequency deviation. Referring to the National Power System Security and Stability Guidelines, in this embodiment, the maximum system frequency deviation constraint is set to 0.2Hz.

[0135] 6. Based on the economic requirements of the power station, an objective function is established to minimize the frequency regulation reserve cost reserved at the sending-end base. Weighting coefficients are set for the frequency regulation reserve power of synchronous generators, wind turbines, photovoltaic systems, and energy storage, respectively. In this embodiment, the weighting coefficients for the frequency regulation reserve power of synchronous generators, wind turbines, photovoltaic systems, and energy storage are all set to 0.25.

[0136] 7. Use a commercial solver to optimize the objective function, calculate the optimal solution for each variable that satisfies the constraints, and output the calculation results for each difference step size. The optimization results can be used to generate the frequency modulation parameter optimization results based on the frequency support of the sending and receiving ends of the conventional DC transmission system, as shown in Table 1.

[0137] Table 1. Optimization results of frequency modulation parameters supported by the sending and receiving ends.

[0138] K w1 ]]> K pv1 ]]> K ess1 ]]> H ess1 ]]> [R G1 ]]> [R w1 ]]> [R pv1 ]]> [R ess1 ]]> K dc ]]> H dc ]]> 38 63 63 2 128.4 184.2 800 329.5 49 6

[0139] Synchronously, the frequency curve of the sending-end base station is generated, such as Figure 3 As shown; before optimization, the sending-end frequency dropped rapidly due to disturbances, and although it subsequently fluctuated and recovered, the overall recovery process was relatively slow; after optimization, the sending-end frequency dropped less due to disturbances, and then recovered more smoothly and quickly, showing fast recovery speed and good stability. The frequency curve of the receiving-end power grid is generated, as shown... Figure 4 As shown, before optimization, the frequency at the receiving end drops rapidly and significantly when disturbed, and there are obvious fluctuations during the frequency recovery process; after optimization, the frequency at the receiving end drops slowly and less, and the frequency can recover quickly and smoothly, and the frequency stability of the receiving end power grid is significantly improved.

[0140] Therefore, by adopting the frequency regulation parameter optimization method of the conventional DC transmission system described in this invention, the relevant frequency regulation parameters of the sending-end renewable energy base and the conventional DC transmission system can be calculated to support the frequency of the receiving-end power grid, while ensuring the stability of the sending-end frequency, thereby improving the frequency support level of renewable energy power plants for the power grid and ensuring the safety of power system operation.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for optimizing frequency regulation parameters in a conventional DC transmission system, characterized in that, Includes the following steps: S1. Statistically analyze the parameters of each synchronous generator in the receiving-end power grid, determine the frequency support capability of each synchronous generator in the receiving-end power grid, establish a frequency response model of the inverter-side receiving-end system and perform differential discretization. S2. Based on the frequency change of the receiving-end grid in the receiving-end system frequency response model, calculate the increase in the command value of the constant active power control on the rectifier side, and transmit the increase in the command value to the rectifier side as the active power disturbance of the sending-end new energy base on the rectifier side. S3. The rectifier-side power supply base responds to the active power disturbance through primary frequency regulation and virtual inertia control, increasing power generation to support the receiving-end grid frequency. S4. Establish a frequency modulation parameter optimization model; S5. Use a commercial solver to solve the frequency regulation parameter optimization model and obtain the frequency regulation parameter optimization results of the conventional DC transmission system; In S1, the parameters of the synchronous generator include the inertial time constant. Adjustment coefficient Rated capacity High-pressure cylinder power ratio Reheater time constant Generator kinetic energy, speed deviation amplification factor ; In step S1, the specific process of establishing the frequency response model of the inverter-side receiver system and performing differential discretization includes: S11. Equivalently aggregate different synchronous generators at the receiving end into a single equivalent synchronous machine; S12. Calculate the equivalent inertial time constant at the receiving end of the equivalent synchronizer. Equivalent adjustment coefficient at the receiving end Recharger time constant Power ratio of the receiving end high-pressure cylinder ; ； ； ； ； ； in, For the rated capacity of the receiving end system, For the first i The inertial time constant of a synchronous generator, For the receiving end i The rated capacity of the synchronous generator, r The number of synchronous generators. For the first i The proportion of synchronous generator capacity to the rated capacity of the receiving-end system. For the first i The droop coefficient of the synchronous generator. Indicates the first i The reheater time constant of a synchronous generator. For the first i The power ratio of the high-voltage cylinder of the synchronous generator; S13. Establish a frequency response model of the receiving-end system after grid disturbance based on the rotor motion equation and perform differential discretization. The frequency response model of the receiving-end system is: ； in, For the rated frequency, For the receiving end frequency deviation, The damping coefficient is... This represents the change in primary frequency modulation power of the equivalent synchronous machine at the receiving end. The sum of the power variations of the frequency regulation units in the sending-end new energy base. This represents the change in active power of the load. t For time; The difference form of the difference discretization process is: ； in, For the occurrence Disturbance size at the first end n Frequency deviation per step size The difference step size; The differential form of the change in the primary frequency regulation power of the equivalent synchronous machine after the power grid disturbance at the receiving end is as follows: ； in, For the receiving end equivalent synchronization machine n The increase in active power per step size, , These are the receiving end synchronous generators. n The active power adjustment amount after dead zone and speed governor limiting by a step size. For the primary frequency regulation dead zone of the receiving-end synchronous generator, This is the active power reserve value of the receiving-end synchronous generator.

2. The method for optimizing frequency regulation parameters of a conventional DC transmission system according to claim 1, characterized in that, In S2, the differential form of the increase in the command value for the rectifier-side constant active power control is: ； ； ； ； in, For the rectifier side n The per-unit value of the increment of the active power control command value with a step size. , The first n The power increment of an LCC-HVDC transmission line that passes through dead zone and limiting links in a step size For the first n The theoretical value of the power transmission increment of a step-size LCC-HVDC line. The time constant for additional frequency control, This refers to the transmission limit power of the LCC-HVDC line. Dead zone for instruction calculation, , This is the gain coefficient. Rated transmission power for LCC-HVDC systems.

3. The method for optimizing frequency regulation parameters of a conventional DC transmission system according to claim 2, characterized in that, In S3, the rectifier-side power supply base responds to the active power disturbance through primary frequency regulation and virtual inertia control, specifically as follows: Based on the increase in the active power command value on the rectifier side, the frequency dynamic response process of the sending-end new energy base is characterized by the rotor motion equation, and differential analysis is performed. The differential form is as follows: ； in, For the first time n Frequency deviation per step size The equivalent inertial time constant of the sending-end synchronous generator is... For the rated capacity of the sending-end system, For the first frequency regulation unit of the new energy base at the sending end n -1 step power change.

4. The method for optimizing frequency regulation parameters of a conventional DC transmission system according to claim 3, characterized in that, In S3, the increased power generation includes the primary frequency regulation increased power generation of the synchronous generator in the sending-end new energy base, the droop control increased power generation of the wind turbine, the droop control increased power generation of the photovoltaic power generation unit, and the droop control increased power generation of the energy storage unit. The differential form of the primary frequency regulation power increase of a synchronous generator is as follows: ； in, For the sending end equivalent synchronizer n The increase in active power per step size, , The sending end synchronous generator is the first n The active power adjustment amount after dead zone and speed governor limiting by a step size. For the primary frequency regulation dead zone of the sending-end synchronous generator, This is the active power reserve value for the sending-end synchronous generator. This is the equivalent droop coefficient at the sending end. The time constant of the feed-end reheater. The power ratio of the high-pressure cylinder at the sending end. The rated power of the sending-end synchronizer; The differential form of the power generation increase through wind turbine droop control is as follows: ； in, For the first wind turbine unit at the sending end n The increase in active power per step size, , The first wind turbine units at the sending end n The active power adjustment amount after dead zone and limiting of each step size This is the primary frequency regulation dead zone for the sending-end wind turbine unit. Reserve power for the sending-end wind turbine units. The time constant of the sending-end wind turbine inverter. The rated power of the wind turbine generator at the sending end. This is the equivalent droop coefficient for the fan; The differential form of the increased power generation due to droop control of photovoltaic power generation units is as follows: ； in, For the first photovoltaic power generation unit at the sending end n The increase in active power per step size, , These are the first photovoltaic power generation units at the sending end. n The active power adjustment amount after dead zone and limiting of each step size This is the primary frequency regulation dead zone for the sending-end photovoltaic power generation unit. Reserve power for the photovoltaic power generation units at the sending end. The time constant of the inverter in the sending-end photovoltaic power generation unit. The rated power of the photovoltaic power generation unit at the sending end. This is the photovoltaic equivalent droop factor; The differential form of the power generation increase controlled by the droop control of the energy storage unit is as follows: ； ； ； ； in, For the first sending-end energy storage unit n The per-unit value of the increased active power at each step size. , These are the first and second generation energy storage units at the sending end. n The active power adjustment amount after dead zone and limiting of each step size For the primary frequency regulation dead zone of the sending-end energy storage unit, Reserve power for the sending-end energy storage unit. The time constant of the inverter in the sending-end energy storage unit. The equivalent virtual inertia coefficient for energy storage, This is the energy storage equivalent droop coefficient. This is the rated power of the sending-end energy storage unit.

5. The method for optimizing frequency regulation parameters of a conventional DC transmission system according to claim 4, characterized in that, In step S4, establishing the frequency modulation parameter optimization model includes the following steps: S41. With the goal of minimizing the active power reserve of renewable energy in the sending-end renewable energy base, establish the objective function of the optimization model. The objective function is: ； in, , , , Cost coefficients are reserved for frequency regulation backups for the sending-end synchronous machine, wind turbine, photovoltaic power generation unit, and energy storage unit, respectively. S42. Based on the frequency stability requirements of the power system, establish the constraints of the optimization model.

6. The method for optimizing frequency regulation parameters of a conventional DC transmission system according to claim 5, characterized in that, In step S42, the constraint establishment includes the following steps: S421. Establish constraints for the active power reserve of frequency regulation units during the frequency support process of the sending-end new energy base: ； in, , , , These are the pre-set active power reserves of new energy synchronous generators, wind turbines, photovoltaic power generation units, and energy storage units, respectively, relative to their rated power. S422. Based on the power system frequency stability guidelines, establish stability constraints for the lowest frequency points of the sending-end and receiving-end systems after disturbances: ； ； in, This indicates the minimum limit of the sending-end base frequency. This indicates the minimum frequency limit of the receiving system.

7. The method for optimizing frequency regulation parameters of a conventional DC transmission system according to claim 6, characterized in that: The frequency regulation parameters of the conventional DC transmission system include the sending-end system parameters and the conventional DC transmission system parameters; The parameters of the sending-end system include: the equivalent droop coefficient of the fan. Photovoltaic equivalent droop coefficient Energy storage equivalent droop coefficient Energy storage equivalent inertial time constant Reserved power capacity for thermal power plants Reserved power capacity for wind turbine units Photovoltaic power generation units reserve power for backup The energy storage unit has reserved power for backup. ; Parameters of a conventional DC transmission system include: frequency modulation gain coefficient. , .

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