CN112271739B - Direct current transmission end power grid subsynchronous oscillation risk assessment method under wind-solar-fire deep peak regulation mode - Google Patents
Direct current transmission end power grid subsynchronous oscillation risk assessment method under wind-solar-fire deep peak regulation mode Download PDFInfo
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Abstract
The invention provides a method for evaluating the risk of subsynchronous oscillation of a direct-current transmission end power grid in a wind-solar-fire deep peak shaving mode, and belongs to the technical field of power systems. The method comprises the following steps: collecting subsynchronous oscillation characteristic sample data of a direct current transmission end power grid under the background of wind, light and fire peak regulation; screening subsynchronous oscillation characteristic sample data until the subsynchronous oscillation characteristic sample data meet a convergence condition to obtain subsynchronous oscillation characteristic data; calculating a comprehensive subsynchronous oscillation risk probability coefficient R according to a subsynchronous oscillation risk comprehensive evaluation model SSO (t); according to the comprehensive subsynchronous oscillation risk probability coefficient R SSO And (t) evaluating the sub-synchronous oscillation risk of the direct current transmission end power grid in the wind-solar-fire deep peak regulation mode. According to the method, a direct current sending end subsynchronous oscillation risk evaluation model under a wind-light-fire peak regulation mode is established, subsynchronous oscillation risk evaluation accuracy is improved, effective data support is provided for power grid dispatching, stable operation of a power grid is maintained, and operation and maintenance reliability of the power grid is enhanced.
Description
Technical Field
The invention belongs to the technical field of power systems, and particularly relates to a method for evaluating the risk of subsynchronous oscillation of a direct-current transmission end power grid in a wind-solar-fire deep peak shaving mode.
Background
In actual power grid operation, in order to maintain the power grid operation stability in a wind, light and fire peak regulation mode, various modes of wind, light and fire are often adopted to maintain the power grid stability by peak clipping and valley filling. However, in actual operation, the parameters of each generator set of the wind power plant, the photovoltaic power plant and the thermal power plant are different, so that the corresponding operation mode and the control parameters are different, the distribution geographical positions of the generator sets are different, the short circuit ratio of the grid-connected point is reduced due to the increase of the grid-connected quantity and the types of the generator sets, and a weak alternating current system is formed, so that the risk of subsynchronous oscillation is very likely to occur in the deep peak shaving mode of wind, light and fire. The existing evaluation method for the sub-synchronous oscillation risk of the direct current sending end power grid is poor in accuracy, difficult to realize comprehensive evaluation and incapable of meeting the evaluation requirement of the sub-synchronous oscillation risk of the direct current sending end power grid in a wind-light-fire deep peak regulation mode.
Disclosure of Invention
In view of the above, the invention provides a method for evaluating the risk of subsynchronous oscillation of a direct-current transmission end power grid in a wind-light-fire deep peak shaving mode, so as to solve the technical problems that the evaluation method for the risk of subsynchronous oscillation of the direct-current transmission end power grid in the prior art is poor in accuracy and cannot meet the evaluation requirement for the risk of subsynchronous oscillation of the direct-current transmission end power grid in the wind-light-fire deep peak shaving mode.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a direct current transmission end power grid subsynchronous oscillation risk assessment method under a wind-solar-fire deep peak regulation mode comprises the following steps:
acquiring subsynchronous oscillation characteristic sample data of a direct current transmission end power grid under the background of wind-solar-fire peak regulation;
screening subsynchronous oscillation characteristic sample data until the subsynchronous oscillation characteristic sample data meet a convergence condition to obtain subsynchronous oscillation characteristic data;
calculating a comprehensive subsynchronous oscillation risk probability coefficient R according to a subsynchronous oscillation risk comprehensive evaluation model SSO (t); the subsynchronous oscillation risk comprehensive evaluation model is shown as the formula I:
in the formula, gamma is the deviation of the grid connection process and the quasi-synchronization condition under the actual wind-light-fire peak regulation mode; i is s The current is the impact current generated when deviation occurs; m n The electromagnetic moment generated when deviation occurs; theta PLn Representing the corresponding output phase angle of the wind, light and fire; c fln Series compensation capacitors corresponding to the wind-solar-fire three-side loop; t is L Low amplitude torsional vibration for a long time; d fs The shafting is damaged due to long-time low-amplitude torsional vibration accumulation; zr is the wind resistance value in the wind turbine generator; h is 1 、h 2 、h 3 Respectively are damping characteristic coefficients corresponding to wind, light and fire; omega is the angular velocity of the rotating machine of the brake disk, rad.s -1 (ii) a p represents a differential operator; m ACn When non-synchronous paralleling with 120 degrees phase angle is output, electromagnetic torque corresponding to the three-side loop of the wind-light fire is output; r gn The parasitic resistance is corresponding to the wind-light-fire three-side loop; rho n The ratio of the wind, light and fire to the corresponding network is obtained; l is a radical of an alcohol fln The filter inductor corresponds to wind, light and fire; eta n Representing the corresponding transmission efficiency of the wind, light and fire line; f TV Electromechanical torsional vibration of a thermal power generating unit; t is LC The compensation tolerance of the series compensation capacitor and the loop is set; c SCn Series compensation capacitors corresponding to the wind-solar-fire circuit; t is t 0 To generate an asynchronous motor effect threshold;
according to the comprehensive subsynchronous oscillation risk probability coefficient R SSO (t), evaluating the sub-synchronous oscillation risk of the direct current transmission end power grid in the wind-solar-fire deep peak regulation mode; wherein the probability coefficient R is the risk probability coefficient according to the comprehensive subsynchronous oscillation SSO (t) evaluating the subsynchronous oscillation risk of the direct-current transmission end power grid in the wind-solar-fire deep peak regulation mode, comprising the following steps of:
when at
0＜t≤t 0 When within the constraint range, R SSO (t) is less than 0.32, the evaluation result is that the subsynchronous oscillation risk is high; otherwise, the evaluation result is that the subsynchronous oscillation risk is low;
when at
t 0 ＜t≤t max Within the restricted range, R is more than 0.84 SSO (t) is less than or equal to 1, the evaluation result is that the subsynchronous oscillation risk is high; otherwise, the evaluation result is that the risk of subsynchronous oscillation is low.
Preferably, the step of screening the subsynchronous oscillation feature sample data until the subsynchronous oscillation feature sample data meets the convergence condition to obtain the subsynchronous oscillation feature data includes the following steps:
adopting a convergence model to output power to the wind, light and fire three ends
Screening to obtain effective convergence wind-light-fire three-terminal output power
Wherein k is<n；P 1,tk 、P 2,tk 、P 3,tk And respectively representing the output power of the wind-solar-fire three ends at the time t.
Preferably, the convergence model is as shown in formula ii:
in the formula, P 1,t max 、P 2,t max 、P 3,t max Respectively representing the maximum value of the output power of the wind-solar-fire three ends at the moment t; eta 1 max 、η 2 max 、η 3 max Respectively, represent the maximum value of the transmission efficiency of the wind, solar and fire line.
Preferably, the damage D of the shafting caused by long-time low-amplitude torsional vibration accumulation is calculated by the formula III fs ：
In the formula, U (t) is a voltage time function which is output in a mixed mode except for an actual measured value and is related to time under a wind-solar-fire depth peak regulation mode; u' (t) is the derivative of U (t).
Preferably, the damping characteristic coefficient h corresponding to wind-solar fire is calculated by the formula IV 1 、h 2 And h 3 。
Preferably, the electromagnetic moment M generated by the deviation is calculated by formula V n
Wherein C is a fixed constant, and is related to the characteristics of the respective motors; u shape n Inputting a voltage; x 20 Is a rotor leakage inductance; s n Is the slip.
Preferably, when asynchronous paralleling with 120-degree output phase angle is calculated through the formula VI, the electromagnetic moment M corresponding to the three-side loop of the wind-light fire is calculated ACn ：
In the formula, phi scc The shafting torsional vibration of the steam turbine generator unit caused by series capacitance compensation; i is the input current.
Preferably, the electromechanical torsional vibration F of the thermal power generating unit is calculated through the formula VII TV 。
Preferably, the series compensation capacitance and the loop compensation tolerance T are calculated by the formula VIII LC 。
According to the technical scheme, the invention provides a method for evaluating the sub-synchronous oscillation risk of a direct current transmission end power grid in a wind-light-fire deep peak regulation mode, which has the beneficial effects that: the method comprises the steps of establishing a direct current sending end subsynchronous oscillation risk assessment model under a wind-light-fire peak regulation mode, comprehensively assessing a power grid subsynchronous oscillation risk of a direct current sending end under a wind-light-fire deep peak regulation mode, improving subsynchronous oscillation risk assessment accuracy, providing effective data support for power grid scheduling, maintaining stable operation of a power grid, and enhancing operation and maintenance reliability of the power grid.
Drawings
FIG. 1 is a flow chart of a direct current transmission end power grid subsynchronous oscillation risk assessment method in a wind-solar-fire deep peak shaving mode.
Detailed Description
The technical scheme and the technical effect of the invention are further elaborated in the following by combining the drawings of the invention.
Referring to fig. 1, in an embodiment, a method for evaluating a risk of subsynchronous oscillation of a dc transmission-side power grid in a wind-solar-fire deep peak shaving mode includes the following steps:
acquiring subsynchronous oscillation characteristic sample data of a direct current transmission end power grid under the background of wind-solar-fire peak regulation;
screening subsynchronous oscillation characteristic sample data until the subsynchronous oscillation characteristic sample data meet a convergence condition to obtain subsynchronous oscillation characteristic data;
calculating a comprehensive subsynchronous oscillation risk probability coefficient R according to a subsynchronous oscillation risk comprehensive evaluation model SSO (t); the subsynchronous oscillation risk comprehensive evaluation model is shown as the formula I:
in the formula, gamma is the deviation of the grid connection process and the quasi-synchronization condition under the actual wind-light-fire peak regulation mode; i is s The current is the impact current generated when deviation occurs; m n The electromagnetic moment generated when deviation occurs; theta PLn Representing the corresponding output phase angle of wind, light and fire; c fln Series compensation capacitors corresponding to the wind-solar-fire three-side loop; t is L Is longTime low amplitude torsional vibration; d fs The shafting is damaged due to long-time low-amplitude torsional vibration accumulation; zr is the wind resistance value in the wind turbine generator; h is 1 、h 2 、h 3 Respectively damping characteristic coefficients corresponding to wind, light and fire; omega is the angular velocity of the rotating machine of the brake disk, rad.s -1 (ii) a p represents a differential operator; m ACn When non-synchronous paralleling with 120 degrees phase angle is output, electromagnetic torque corresponding to the three-side loop of the wind-light fire is output; r gn The parasitic resistance is corresponding to the wind-light-fire three-side loop; rho n The ratio of the wind, light and fire to the corresponding network is obtained; l is fln The filter inductor corresponds to wind, light and fire; eta n Representing the transmission efficiency corresponding to the wind, light and fire line; f TV Electromechanical torsional vibration of a thermal power generating unit; t is LC The compensation tolerance of the series compensation capacitor and the loop is set; c SCn Series compensation capacitors corresponding to the wind-solar-fire circuit; t is t 0 To generate an asynchronous motor effect threshold;
according to the comprehensive subsynchronous oscillation risk probability coefficient R SSO And (t) evaluating the sub-synchronous oscillation risk of the direct current transmission end power grid in the wind-solar-fire deep peak regulation mode.
Specifically, the probability coefficient R according to the comprehensive subsynchronous oscillation risk SSO (t) evaluating the subsynchronous oscillation risk of the direct-current transmission end power grid in the wind-solar-fire deep peak regulation mode, comprising the following steps of:
when at
0＜t≤t 0 When within the constraint range, R SSO (t) is less than 0.32, the evaluation result is that the subsynchronous oscillation risk is high; otherwise, the evaluation result is that the subsynchronous oscillation risk is low;
when at
t 0 ＜t≤t max Within the restricted range, R is more than 0.84 SSO (t) is less than or equal to 1, the evaluation result is that the subsynchronous oscillation risk is high; otherwise, the evaluation result is that the risk of subsynchronous oscillation is low.
In a specific embodiment, wind, light and fire peak regulation is collectedThe subsynchronous oscillation characteristic sample data of the direct current transmission end power grid under the background comprises the following steps of collecting relevant parameter data which are easy to cause subsynchronous oscillation for the direct current transmission end power grid under the background of wind, light and fire peak regulation, wherein relevant parameters at the power grid side mainly comprise: wind power grid point voltage U WP Photovoltaic grid-connected point voltage U PV Thermal power grid-connected point voltage U TP Wind power grid point current I WP Photovoltaic grid-connected point current I PV Grid-connected point current I of thermal power TP The output power of the wind, light and fire three ends is P 1,t 、P 2,t 、P 3,t (ii) a Filter capacitor C fln Filter inductor L fln . The measured parameters in the control circuit include: theta PLn And the corresponding output phase angle of the wind-solar fire is shown. Eta n Representing transmission efficiency and small-voltage signal disturbance value of corresponding wind-solar-fire line
Small signal disturbance value of current
Corresponding parasitic resistance R gn Network occupation ratio rho corresponding to wind, light and fire n Subsynchronous oscillation risk probability index R SSO (t) of (d). The subscript n is 1, 2 and 3 respectively corresponding to the wind-light-fire corresponding parameters. The shafting torsional vibration of the steam turbine generator unit caused by direct current transmission is phi dct The shafting torsional vibration of the turbo generator set caused by series capacitance compensation is phi scc 。
And after the data are collected, screening out values which accord with the load characteristics for calculation, and establishing a direct current transmission end power grid torsional vibration coefficient equation under the wind-solar-fire deep peak regulation mode.
For example, data is combined
Screening by substituting constraint conditions of formula (II) to obtain effective convergence data
Where n > k, P 1,tk 、P 2,tk 、P 3,tk And respectively representing the output power of the wind-solar-fire three ends at the time t. The constraint judgment conditions for the wind, light and fire data convergence screening are as follows:
in the formula, P 1,t max 、P 2,t max 、P 3,t max Respectively representing the maximum value of the output power of the three terminals of the wind-solar fire at the moment t; eta 1 max 、η 2 max 、η 3 max Respectively, represent the maximum value of the transmission efficiency of the wind, solar and fire line.
In the wind-light-fire deep peak regulation mode, the wind-light-fire three-side loop series compensation capacitors of the direct-current transmission end power grid are respectively represented as C fl1 、C fl2 、C fl3 When a thermal power generating unit steam turbine generates torsional stress to cause damage to a shaft system, low-amplitude torsional vibration T is generated for a long time L Accumulation of damage to shafting D fs At a critical value t 0 The pre-induced asynchronous motor effect is expressed as formula III:
in the formula, U (t) is a voltage time function which is output in a mixed mode except for an actual measured value and is related to time under a wind-solar-fire depth peak regulation mode; u' (t) is the derivative of U (t).
Because the parameter models of all the generator sets are different, after a shafting is damaged, the wind resistance value of a typical structure of a fan in the wind turbine generator set is taken as
Correspondingly solving the damping characteristic curve corresponding to wind, light and fire as a formula IV:
in a direct current sending end power grid combined node in an actual wind-light-fire peak regulation mode, quasi-synchronization conditions are difficult to completely meet in a grid connection process, and an impact current I is generated when a deviation gamma occurs S And the impact current and the deviation are in direct proportion, and the linear expression is I S ＝γcosθ PLn (t) I, the relationship of the magnitude of the electromagnetic torque generated at the same time is V
Wherein C is a fixed constant, and is related to the characteristics of the respective motors; u shape n Inputting a voltage; x 20 Is a rotor leakage inductance; s n Is the slip. At theta PLL When the switch is switched on at a deviation angle of 180 degrees, the impact current is the largest, and at the moment, the most serious asynchronous parallel condition is generally considered; the probability of subsynchronous oscillation occurring is greatly increased. The subsynchronous oscillation risk probability at this time is:
if the relationship between the electromechanical interaction and the subsynchronous oscillation is considered, first, from the viewpoint of torsional oscillation analysis of the axis system of the unit, when the closing angle is theta PLn When the wind-solar-thermal power generation device is parallel to about 120 degrees, the electromagnetic torque is the largest, the torsional vibration response of a shafting is the most serious, and therefore the wind-solar-thermal power generation device corresponds to the wind-solar-thermal voltage U WP 、U PV 、U TP The phase angle difference of 120 degrees is taken as the key point of torsional vibration analysis, and electromagnetic moment expressions which correspond to 120 degrees and are not in parallel in the same period can be obtained according to empirical formulasⅥ：
Where ω is the angular velocity of the rotating machine of the brake disk, rad · s -1 And I is the input current. For the obtained result M ACn Taking absolute value, and solving the electromechanical torsional vibration F of the thermal power generating unit in the next step TV Solving the output (shown in formula VII).
In the formula, p represents a differential operator.
Secondly, in a scene of wind, light and fire deep peak regulation, the proportion of the three is adjusted along with the gradual increase of time, and in an initial stage, in a scene of small proportion of fire participation, the whole tends to be stable, and along with the increase of power consumption at a load side, the participation proportion at the current stage cannot maintain the continuous long-term stable operation of a power grid. The input proportion of the thermal power generating unit is increased, and deep peak regulation is participated. At this time, each line is connected in series with a compensation capacitor C SCn Tends to be unstable, is easy to generate unstable oscillation phenomenon, and has series compensation capacitor and loop compensation tolerance T LC The transfer function between them is as in formula VIII.
Electromechanical torsional vibration output F of thermal power generating unit TV In deep peak-shaving mode, series compensation capacitor C SCn Under action, the relation becomes:
the subsynchronous oscillation risk probability index at this time is expressed as:
integrating the above expression, under the electromechanical torsional vibration interaction and in a relevant scene, the subsynchronous oscillation risk probability is:
synthesizing subsynchronous oscillation risk probability parameters, and increasing the proportion of thermal power participation in the wind-solar-thermal deep peak regulation mode at a critical value t 0 Before, the asynchronous motor effect is generated, the risk probability of subsynchronous oscillation is improved, and when t 0 ＜t＜t max When the proportion of the thermal power is more than 60%, the asynchronous motor effect is gradually reduced, but the probability trend of the associated subsynchronous oscillation risk is gradually reduced due to the fact that the electromagnetic torque of the unit is increased and the torsional vibration of the derivative machine is acted, but when the proportion of the thermal power is more than 60%, the probability trend of the associated subsynchronous oscillation risk is gradually reduced
The risk probability is increased sharply, and in conclusion, the subsynchronous oscillation risk comprehensive evaluation index is shown as formula I:
the technical scheme and technical effects of the present invention are further described below by a specific embodiment.
According to a certain place in northeast, the following data are actually measured, wherein the relevant parameters of the power grid side mainly comprise: wind power grid point voltage U WP 660V, photovoltaic grid-connected point voltage U PV 380V, thermal power grid point voltage U TP 35kV, wind power grid point current I WP 12A, photovoltaic grid-connected point current I PV 18.2A, thermal power point-connected current I TP 60A. Filter capacitor C fl 500 muF, filter inductance L fl At 100 μ F, the measured parameters in the control circuit include: eta n ＝[70％:65％:60％]Representing transmission efficiency of corresponding wind, light and fire lines and corresponding parasitic resistance
Taking a typical participation proportion rho under two actual wind-solar fire depth peak regulation modes n ＝[ρ 1 ,ρ 2 ]Respectively, [ 50%: 30%: 20 percent of]、[30％：20％：50％]。
And after the data are collected, screening out values which accord with the load characteristics for calculation, and establishing a direct current transmission end power grid torsional vibration coefficient equation under the wind-solar-fire deep peak regulation mode.
Data to be recorded
Screening is carried out in place of the constraint conditions of formula (II). Substituting the data, and screening to obtain effective convergence data
In the wind-light-fire deep peak regulation mode, the wind-light-fire three-side loop series compensation capacitors of the direct-current transmission end power grid are respectively represented as C fl1 ＝500μF、C fl2 ＝450μF、C fl3 ＝550μF，T L D is obtained from formula iii, wherein 1499.95 is about 1500 fs ＝325。
Because the parameter models of all the generator sets are different, after a shafting is damaged, the wind resistance value of a typical structure of a fan in the wind turbine generator set is taken as
Correspondingly solving the damping characteristic typical solution corresponding to wind, light and fire as follows:
wherein
Find h 1 ＝3.25，h 2 ＝6.98，h 3 ＝5.74。
In a direct current sending end power grid combined node in an actual wind-light-fire peak regulation mode, quasi-synchronization conditions are difficult to completely meet in a grid connection process, and an impact current I is generated when a deviation gamma occurs S And the impact current and the deviation are in direct proportion, and the linear expression is I S ＝γcosθ PLL I, the magnitude relation of the electromagnetic torque generated simultaneously is
Wherein, C ═ 36; u shape n ＝380V；X 20 1000 Ω is the leakage inductance of the rotor; s n 0.6. At theta PLn When the switch is switched on at a deviation angle of 180 degrees, the impact current is the largest, and at the moment, the most serious asynchronous parallel condition is generally considered; the probability of subsynchronous oscillation occurring is greatly increased. The subsynchronous oscillation risk probability at this time is:
to obtain
From the angle of torsional vibration analysis of a unit shafting, when the closing angle is theta PLL When the wind-solar-thermal power generation device is parallel to about 120 degrees, the electromagnetic torque is the largest, the torsional vibration response of a shafting is the most serious, and therefore the wind-solar-thermal power generation device corresponds to the wind-solar-thermal voltage U WP 、U PV 、U TP The phase angle difference of 120 degrees is taken as the key point of torsional vibration analysis, and according to the formula VI, the electromagnetic moments M corresponding to 120 degrees when in non-synchronous parallel can be obtained ACn ＝[60 85 42]. Where ω is 87.82, rad · s -1 . For the obtained result M ACn Taking an absolute value, and carrying out next step on solving the electromechanical torsional vibration F of the thermal power generating unit through a formula VII TV Solving of the output to obtain F TV ＝1065。
Step 3.2: p represents a differential operator. In the scene of wind, light and fire depth peak regulation, the proportion of the three is adjusted along with the gradual increase of time, in the initial stage, in the scene of small proportion of the thermal power, the whole tends to be stable, and along with the increase of the power consumption at the load side, the proportion of the thermal power cannot maintain the continuous long-term stable operation of the power grid in the current stage. The input proportion of the thermal power generating unit is increased, and deep peak regulation is participated. At the moment, each line is connected with a compensation capacitor C in series SCn Tends to be unstable, is easy to generate unstable oscillation phenomenon, and has series compensation capacitor and loop compensation tolerance T LC The transfer function between is as follows.
Find T LC (S) and inverse Laplace transform to obtain T LC ＝0.68
Electromechanical torsional vibration output F of thermal power generating unit TV In deep peak-shaving mode, series compensation capacitor C SCn Under the action of the action, the relational expression becomes
The subsynchronous oscillation risk probability index is expressed as
Step 3.3: integrating the above expression, under the electromechanical torsional vibration interaction and in relevant scenes, the subsynchronous oscillation risk probability is as follows:
finishing to obtain:
synthesizing subsynchronous oscillation risk probability parameters, and increasing the proportion of thermal power participation in the wind-solar-thermal deep peak regulation mode at a critical value t 0 Before, the asynchronous motor effect is generated, the risk probability of subsynchronous oscillation is improved, and when t 0 ＜t＜t max When the proportion of the thermal power is more than 60%, the asynchronous motor effect is gradually reduced, but the probability trend of the associated subsynchronous oscillation risk is gradually reduced due to the fact that the electromagnetic torque of the unit is increased and the torsional vibration of the derivative machine is acted, but when the proportion of the thermal power is more than 60%, the probability trend of the associated subsynchronous oscillation risk is gradually reduced
The risk probability is increased sharply, and in conclusion, the subsynchronous oscillation risk comprehensive evaluation index is
Wherein the content of the first and second substances,
when at
0＜t≤t 0 When within the constraint range, R SSO And (t) is less than 0.32, the subsynchronous oscillation risk probability is considered to be extremely high, and the wind-light fire output is effectively adjusted to perform adjustment.
When at
t 0 ＜t≤t max Within the restricted range, R is more than 0.84 SSO And (t) is less than or equal to 1, namely the subsynchronous oscillation risk probability is considered to be extremely high, at the moment, the participation proportion of the line capacitance is effectively adjusted, and the line is overhauled to be effectively adjusted.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
Claims (9)
1. A method for evaluating the risk of subsynchronous oscillation of a direct-current transmission end power grid in a wind-solar-fire deep peak regulation mode is characterized by comprising the following steps of:
acquiring subsynchronous oscillation characteristic sample data of a direct current transmission end power grid under the background of wind-solar-fire peak regulation;
screening subsynchronous oscillation characteristic sample data until the subsynchronous oscillation characteristic sample data meet a convergence condition to obtain subsynchronous oscillation characteristic data;
calculating a comprehensive subsynchronous oscillation risk probability coefficient R according to a subsynchronous oscillation risk comprehensive evaluation model SSO (t)；
The subsynchronous oscillation risk comprehensive evaluation model is shown as the formula I:
in the formula, gamma is the deviation of the grid connection process and the quasi-synchronization condition under the actual wind-light-fire peak regulation mode; i is s The current is the impact current generated when deviation occurs; m n The electromagnetic moment generated when deviation occurs; theta PLn Representing the corresponding output phase angle of the wind, light and fire; c fln Series compensation capacitors corresponding to the wind-solar-fire three-side loop; t is L Low amplitude torsional vibration for a long time; d fs The shafting is damaged due to long-time low-amplitude torsional vibration accumulation; zr is the wind resistance value in the wind turbine generator; h is 1 、h 2 、h 3 Respectively are damping characteristic coefficients corresponding to wind, light and fire; omega is the angular velocity of the rotating machine of the brake disk, rad.s -1 (ii) a p represents a differential operator; m ACn When non-synchronous paralleling with 120 degrees phase angle is output, electromagnetic torque corresponding to the three-side loop of the wind-light fire is output; r gn Is the wind and lightParasitic resistance corresponding to the three-side loop; ρ is a unit of a gradient n The ratio of the wind, light and fire to the network is respectively; l is fln The filter inductors are respectively corresponding to wind, light and fire; eta n Representing the transmission efficiency corresponding to the wind, light and fire line; f TV Electromechanical torsional vibration of a thermal power generating unit; t is LC The compensation tolerance of the series compensation capacitor and the loop is set; c SCn Series compensation capacitors corresponding to the wind-solar-fire circuit; t is t 0 To generate an asynchronous motor effect threshold;
according to the comprehensive subsynchronous oscillation risk probability coefficient R SSO (t), evaluating the sub-synchronous oscillation risk of the direct current transmission end power grid in the wind-solar-fire deep peak regulation mode; wherein the probability coefficient R is the risk probability coefficient according to the comprehensive subsynchronous oscillation SSO (t) evaluating the subsynchronous oscillation risk of the direct-current transmission end power grid in the wind-solar-fire deep peak regulation mode, comprising the following steps of:
when at
When within the constraint range, R SSO (t) is less than 0.32, the evaluation result is that the subsynchronous oscillation risk is high; otherwise, the evaluation result is that the subsynchronous oscillation risk is low;
when at
Within the restricted range, R is more than 0.84 SSO (t) is less than or equal to 1, the evaluation result is that the subsynchronous oscillation risk is high; otherwise, the evaluation result is that the risk of subsynchronous oscillation is low.
2. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid under the wind-solar-fire deep peak shaving mode according to claim 1, wherein the step of screening subsynchronous oscillation characteristic sample data until the subsynchronous oscillation characteristic sample data meets a convergence condition to obtain the subsynchronous oscillation characteristic data comprises the following steps: adopting a convergence model to output power to the wind, light and fire three ends
Screening to obtain effective convergence wind-light-fire three-terminal output power
Wherein k is<n；P 1,tk 、P 2,tk 、P 3,tk And respectively representing the output power of the wind-solar-fire three ends at the time t.
3. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid in the wind-solar-fire deep peak shaving mode according to claim 2, wherein the convergence model is as shown in formula II:
in the formula, P 1,t max 、P 2,t max 、P 3,t max Respectively representing the maximum value of the output power of the wind-solar-fire three ends at the moment t; eta 1 max 、η 2 max 、η 3 max Respectively, represent the maximum value of the transmission efficiency of the wind, solar and fire line.
4. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid in the wind-solar-fire deep peak regulation mode according to claim 1, wherein the method for evaluating the risk of shafting damage D caused by long-time low-amplitude torsional oscillation accumulation through formula III fs ：
In the formula, U (t) is a voltage time function which is output in a mixed mode except for an actual measured value and is related to time under a wind-solar-fire depth peak regulation mode; u' (t) is the derivative of U (t).
5. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid in the wind-solar-fire deep peak shaving mode according to claim 1, wherein the method is characterized in thatAnd calculating the damping characteristic coefficient h corresponding to wind-light fire by the formula IV 1 、h 2 And h 3 ：
6. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid in the wind, light and fire deep peak regulation mode according to claim 1, wherein the deviation is calculated by formula V to generate the electromagnetic moment M n ：
Wherein C is a fixed constant, and is related to the characteristics of the respective motors; u shape n Inputting a voltage; x 20 Is a rotor leakage inductance; s n Is the slip.
7. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid under the wind-solar-fire deep peak regulation mode according to claim 1, wherein the electromagnetic moment M corresponding to the wind-solar-fire three-side loop when asynchronous paralleling with an output phase angle of 120 degrees is calculated through a formula VI ACn ：
In the formula, phi scc For vapour caused by series capacitance compensationShafting torsional vibration of the wheel generator set; i is the input current.
8. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid under the wind-solar-fire deep peak shaving mode according to claim 1, characterized in that the electromechanical torsional oscillation F of the thermal power generating unit is calculated through a formula VII TV ：
9. The method for evaluating the risk of subsynchronous oscillation of the direct-current transmission-end power grid in the wind-solar-fire deep peak shaving mode according to claim 1, wherein the series compensation capacitance and the loop compensation tolerance T are calculated according to a formula VIII LC ：
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