阅读说明：本技术 一种抑制直流连续换相失败的交直流混联系统功率协调控制方法 (AC-DC series-parallel system power coordination control method for inhibiting DC continuous commutation failure ) 是由 岳东 丁苍璧 周霞 戴剑丰 窦春霞 张智俊 李兆伟 胡阳 郄朝辉 刘福锁 李威 于 2021-08-09 设计创作，主要内容包括：本发明公开了一种抑制直流连续换相失败的交直流混联系统功率协调控制方法,其包括：当系统面临连续换相失败风险时,通过调节逆变侧直流电流指令降低直流传输系统有功功率,进而抑制直流连续换相失败；同时监测交直流混联系统的潮流变化,对交流传输系统进行过载风险判断；若存在过载风险,则启动火电机组调频系统降低有功输出,若火电厂调节水平无法有效减小系统潮流大范围波动,则采用风电机组主动功率控制的方法调节送端电网有功输出,降低交流传输系统过载危害。本发明方法既能够抑制直流连续换相失败,又能降低交流传输系统过载现象风险,有效地保证了含高比例风电送端电网交直流混联系统功率协调控制的灵活性、快速性和经济性。(The invention discloses a power coordination control method of an alternating current-direct current hybrid system for inhibiting direct current continuous commutation failure, which comprises the following steps: when the system is in the risk of continuous commutation failure, the active power of the direct current transmission system is reduced by adjusting the direct current instruction of the inversion side, and the direct current continuous commutation failure is further inhibited; meanwhile, the tidal current change of the alternating current and direct current hybrid system is monitored, and overload risk judgment is carried out on the alternating current transmission system; and if the overload risk exists, starting a frequency modulation system of the thermal power plant to reduce the active output, and if the regulation level of the thermal power plant cannot effectively reduce the large-range fluctuation of the system tide, regulating the active output of a power grid at a sending end by adopting a method of active power control of a wind turbine generator, so as to reduce the overload hazard of the alternating current transmission system. The method can inhibit the direct current continuous commutation failure, reduce the overload risk of the alternating current transmission system, and effectively ensure the flexibility, rapidity and economy of the power coordination control of the alternating current-direct current hybrid system of the power grid containing the high-proportion wind power transmission end.)

1. A power coordination control method for an alternating current-direct current hybrid system for restraining direct current continuous commutation failure is characterized by comprising the following steps:

when the direct current transmission system has direct current commutation failure, the active power of the direct current transmission system is reduced through an inversion side direct current instruction, and the direct current continuous commutation failure is restrained;

when the direct current phase conversion failure occurs in the direct current transmission system, carrying out overload risk judgment on the alternating current transmission system in the alternating current and direct current hybrid system according to the power flow change of the alternating current and direct current hybrid system containing the high-proportion wind power transmission end power grid;

and according to the overload risk judgment result, if the alternating current transmission system has the overload risk, regulating the active power output of the power grid at the sending end by using the thermal power generating unit and the wind power generating unit, and reducing the overload risk of the alternating current transmission system.

2. The method for power coordination control of the alternating current-direct current hybrid system for inhibiting direct current continuous commutation failure according to claim 1, wherein the method for inhibiting direct current continuous commutation failure comprises the following steps:

obtaining a relation between active power transmission and reactive power consumption of a direct current transmission system:

wherein Q is_dcRepresenting reactive power, P, of a DC transmission system_dcThe active power of the direct current transmission system is represented, phi represents the power factor of the direct current transmission system, gamma is the extinction angle of the converter valve on the inversion side of the direct current transmission system, and beta is the advanced trigger angle;

according to a relational expression of active power transmission and reactive power consumption of the direct current transmission system, the active power and the reactive power of the direct current transmission system are in direct proportion; the active power of the direct current transmission system is reduced through the direct current instruction at the inversion side, so that the reactive power requirement of the direct current transmission system during the direct current commutation failure period is reduced, and the direct current continuous commutation failure is restrained.

3. The method for power coordination control of the alternating current-direct current hybrid system for inhibiting the direct current continuous commutation failure according to claim 1, wherein the method for judging the overload risk of the alternating current transmission system in the alternating current-direct current hybrid system comprises the following steps:

when the direct current commutation failure occurs in the alternating current and direct current transmission system containing the high-proportion wind power transmission end power grid, the real-time active transmission P of the alternating current transmission system_acAbove the power transmission limit P of an AC transmission line_aclIf so, it is determined that the AC transmission system is overloadedA phenomenon;

in an alternating current-direct current transmission system containing a high-proportion wind power transmission end power grid, when the inversion side of the direct current transmission system fails to change phase to cause the active power of the direct current transmission system to drop, if delta P_dc＞ΔP_aclJudging that the AC transmission system has overload risk, wherein, Delta P_dcAmplitude, Δ P, representing the active power dip of a DC transmission system_aclRepresenting the ac transmission line power transmission limit increments.

4. The method for power coordination control of the AC-DC hybrid system for restraining the DC continuous commutation failure according to claim 3, wherein the amplitude value Δ P of the active power dip of the DC transmission system_dcThe expression of (a) is as follows:

wherein, Δ P_eRepresenting the variation of the active output of the transmitting end network, delta₁Is E_qAnd U₂Phase angle difference between them, E_qTo the generator terminal voltage, U₂For the B bus voltage of the AC transmission system, theta is U₁And U₂Phase angle between, U₁For the voltage of the transmitting-end network, Δ U₁For the change of voltage of the sending end system, X_dIs a direct-axis reactance of the generator, X_T1And X_T2Respectively equivalent reactance, delta, of transformers on two sides of an AC line in an AC transmission system₁For the power angle variation when the commutation failure occurs in the DC transmission system, Delta theta is U₁And U₂Amount of phase angle change between, X_LIs the reactance of an AC line in an AC transmission system.

5. The power coordination control method for the alternating current-direct current hybrid system for inhibiting the direct current continuous commutation failure according to claim 1, wherein according to the judgment result of overload risk, if the alternating current transmission system has the overload risk, the method for adjusting the active power output of the power grid at the sending end by using the thermal power generating unit and the wind power generating unit comprises the following steps:

analyzing the adjusting capacity of a thermal power generating unit in a power grid containing a high-proportion wind power transmission end to obtain the maximum adjustable active power delta P of the thermal power generating unit_gmax；

If P_acl≤P_ac-ΔP_gmaxAnd reducing the output of the active power of the power grid containing a high-proportion wind power transmission end through frequency modulation control of a thermal power generating unit, wherein P is_aclIndicating the power transmission limit, P, of an AC transmission system_acRepresenting the active transmission quantity of the alternating current transmission system;

if P_acl＞P_ac-ΔP_gmaxAnd under the condition of not cutting off the machine, the active power output of a power grid containing a high-proportion wind power transmission end is reduced by respectively adopting a thermal power generating unit frequency modulation control method and a wind power generating unit active power control method.

6. The method for power coordination control of the AC-DC hybrid system for inhibiting the DC continuous commutation failure according to claim 5, wherein the wind turbine generator active power control method comprises a wind turbine generator active acceleration control method and a fan pitch angle active control method.

7. The method according to claim 6, wherein if P is the number of consecutive commutation failures, the method further comprises_acl＞P_ac-ΔP_gmaxUnder the condition of not cutting off the machine, when the mechanical angular speed of the wind wheel is less than the maximum rotating speed w of the fan_MmaxIn the process, the active power output of a power grid containing a high-proportion wind power transmission end is reduced by respectively adopting a thermal power generating unit frequency modulation control method and a wind power generating unit active acceleration control method; when the wind turbine generator accelerates to the maximum rotating speed w of the fan_MmaxAnd then, if the active power output of the power grid at the transmitting end does not meet the active requirement for reducing the overload risk of the alternating current line, reducing the active power output of the power grid at the transmitting end containing high proportion of wind power by adopting a wind turbine pitch angle active control method on the basis of a frequency modulation control method and a wind turbine active acceleration control method of the thermal power generating unit, and obtaining a coordination control strategy.

8. The method for power coordination control of the alternating current-direct current hybrid system for inhibiting direct current continuous commutation failure according to claim 6, wherein the method for actively accelerating the control of the wind turbine generator comprises the following steps:

the mechanical angular speed of the wind wheel when the wind turbine generator works normally is set as w_MUnder the condition of no cutting machine, the mechanical angular speed of the wind wheel is controlled to be w_MAccelerated to w'_MiChanging the coefficient of wind energy utilization C_pAnd further reducing the active power output of the wind turbine, wherein w_M＜w′_Mi≤w_Mmax，w_MmaxMaximum wind wheel mechanical angular velocity;

the active power output reduced by actively accelerating the mechanical angular speed of the wind wheel is as follows:

wherein, Δ P_wiRepresenting the reduced active power output, P, of the wind turbine after actively accelerating the mechanical angular speed of the wind turbine_wiRepresenting active power output, P 'of the wind turbine generator set during normal operation'_wiRepresenting that the mechanical angular speed of the wind wheel is accelerated to w'_MiThe active power output later, rho is the air density, S is the area of one circle swept by the fan blade, C_pmaxIs the maximum wind energy utilization coefficient, C 'of the wind turbine generator set'_pAccelerating mechanical angular speed of wind wheel to w'_MiAnd v is the input wind speed of the fan.

9. The AC-DC hybrid system power coordination control method for inhibiting DC continuous commutation failure according to claim 8, wherein C'_pThe expression of (a) is as follows:

wherein, beta_wAnd E is a natural index, and R is the radius of the fan blade.

10. The method for power coordination control of the AC-DC hybrid system for inhibiting the DC continuous commutation failure according to claim 6, wherein the active control method for the pitch angle of the fan comprises the following steps:

the blade arranged on the hub is controlled to adjust the pitch angle, the aerodynamic characteristics of the fan blade are changed, and then the active power output by the wind power plant is adjusted by changing the stress conditions of the blade and the whole machine.

Technical Field

The invention relates to a power coordination control method for an alternating current-direct current series-parallel connection system for inhibiting direct current continuous commutation failure, and belongs to the technical field of large power grid stability control.

Background

The wind power base and the thermal power base in China are highly overlapped in distribution areas and are far away from load centers, so that the wind-fire bundling power generation mode is widely applied, and the high-voltage direct-current power transmission system meets the requirements of large-capacity and long-distance power transmission in the wind-fire bundling power generation process. The combination of traditional high voltage alternating current transmission system, wind fire bundling alternating current-direct current series-parallel connection send out the system will be the important development trend of electric power system. The inverter side commutation failure of the high-voltage direct-current transmission system is one of the most common faults of the alternating-current and direct-current series-parallel transmission system, and meanwhile, the commutation failure causes the power of the direct-current transmission system to drop greatly, the system power flow is transferred in a large range, and the alternating-current transmission system is overloaded. Therefore, how to inhibit the continuous direct-current commutation failure and the large fluctuation of the power flow in the alternating-current and direct-current hybrid system is an urgent problem to be solved in the modern power system.

At present, researches on inhibiting continuous commutation failure of a high-voltage direct-current power transmission system are more. In the aspect of design and planning, reactive power compensation equipment such as a Static Var Compensator (SVC) and a static synchronous compensator (STATCOM) can be configured, the reactive voltage supporting capability of a system is improved, and the risk of commutation failure is reduced. In terms of control strategies, currently, an optimized lift method of low-voltage current-limiting controller (VDCOL) and commutation failure prediction Controller (CFPREV) is mainly used. The research of CFPREV is relatively less, and the control method can directly improve the commutation margin according to the advance triggering of the inverter, thereby reducing the risk of commutation failure; the VDCOL limits direct current under a low voltage condition, and reduces active power transmission of a direct current system, so that the occurrence probability of continuous phase commutation failure of the system is reduced.

At present, the research results of the overload phenomenon of an alternating current transmission system in an alternating current and direct current hybrid system are less. Generally, a power flow controller is adopted to improve the steady-state power flow distribution of an alternating current and direct current series-parallel transmission system, but the cost is too high, and the construction difficulty is higher. And no relevant research is available on the regulating strategy of the power impact in the transient process. In a wind-fire bundling AC-DC parallel-serial delivery system, reducing the active power output of a delivery end power grid is the key to solving the problem of large-range transfer of the system tide, a generator tripping load cutting method or a thermal power generating unit frequency modulation method can be generally adopted, the former has the problem of over-cutting, which increases the unnecessary starting and stopping times of the thermal power generating unit and deteriorates the running state of the wind power generating unit, so that the related economic benefit is reduced, and the latter has a very limited effect on power regulation of the delivery end power grid containing high-proportion new energy and cannot effectively treat the problem of system tide fluctuation in time. Therefore, the direct current continuous commutation failure is quickly and effectively inhibited, the overload risk of the alternating current transmission system after the direct current continuous commutation failure is efficiently and economically reduced, and the method has important significance for realizing the safe and stable operation of the wind-fire bundling alternating current-direct current hybrid system.

Disclosure of Invention

In order to solve the problem of insufficient power coordination control of an alternating current-direct current (AC-DC) hybrid transmission system for restraining wind-fire bundling during Direct Current (DC) continuous commutation failure in the prior art, the invention provides a power coordination control method of the AC-DC hybrid transmission system for restraining the DC continuous commutation failure, which analyzes the tidal current distribution characteristic of the AC-DC hybrid transmission system for restraining the wind-fire bundling, restrains the DC continuous commutation failure by reducing the reactive power requirement of the DC transmission system, actively controls the active output of a power grid wind turbine generator at a sending end, reduces the overload phenomenon hazard of the AC transmission system and realizes the power coordination optimization control of the system.

In order to solve the technical problems, the invention adopts the following technical means:

the invention provides a power coordination control method of an alternating current-direct current hybrid system for inhibiting direct current continuous commutation failure, which comprises the following steps:

when the direct current transmission system has direct current commutation failure, the active power of the direct current transmission system is reduced through an inversion side direct current instruction, and the direct current continuous commutation failure is restrained;

when the direct current phase conversion failure occurs in the direct current transmission system, carrying out overload risk judgment on the alternating current transmission system in the alternating current and direct current hybrid system according to the power flow change of the alternating current and direct current hybrid system containing the high-proportion wind power transmission end power grid;

and according to the overload risk judgment result, if the alternating current transmission system has the overload risk, regulating the active power output of the power grid at the sending end by using the thermal power generating unit and the wind power generating unit, and reducing the overload risk of the alternating current transmission system.

Further, the method for inhibiting the direct current continuous commutation failure comprises the following steps:

obtaining a relation between active power transmission and reactive power consumption of a direct current transmission system:

wherein Q is_dcRepresenting reactive power, P, of a DC transmission system_dcThe active power of the direct current transmission system is represented, phi represents the power factor of the direct current transmission system, gamma is the extinction angle of the converter valve on the inversion side of the direct current transmission system, and beta is the advanced trigger angle;

according to a relational expression of active power transmission and reactive power consumption of the direct current transmission system, the active power and the reactive power of the direct current transmission system are in direct proportion; the active power of the direct current transmission system is reduced through the direct current instruction at the inversion side, so that the reactive power requirement of the direct current transmission system during the direct current commutation failure period is reduced, and the direct current continuous commutation failure is restrained.

Further, the method for judging the overload risk of the alternating current transmission system in the alternating current-direct current hybrid system comprises the following steps:

when the direct current commutation failure occurs in the alternating current and direct current transmission system containing the high-proportion wind power transmission end power grid, the real-time active transmission P of the alternating current transmission system_acAbove the power transmission limit P of an AC transmission line_aclJudging that the overload phenomenon occurs in the alternating current transmission system;

in an alternating current-direct current transmission system containing a high-proportion wind power transmission end power grid, when the inversion side of the direct current transmission system fails to change phase to cause the active power of the direct current transmission system to drop, if delta P_dc＞ΔP_aclJudging that the AC transmission system has overload risk, wherein, Delta P_dcAmplitude, Δ P, representing the active power dip of a DC transmission system_aclRepresenting the ac transmission line power transmission limit increments.

Further, the amplitude value delta P of the active power drop of the direct current transmission system_dcThe expression of (a) is as follows:

wherein, Δ P_eRepresenting the variation of the active output of the transmitting end network, delta₁Is E_qAnd U₂Phase angle difference between them, E_qTo the generator terminal voltage, U₂For the B bus voltage of the AC transmission system, theta is U₁And U₂Phase angle between, U₁For the voltage of the transmitting-end network, Δ U₁For the change of voltage of the sending end system, X_dIs a direct-axis reactance of the generator, X_T1And X_T2Respectively equivalent reactance, delta, of transformers on two sides of an AC line in an AC transmission system₁For the power angle variation when the commutation failure occurs in the DC transmission system, Delta theta is U₁And U₂Amount of phase angle change between, X_LIs the reactance of an AC line in an AC transmission system.

Further, according to the overload risk judgment result, if the alternating current transmission system has an overload risk, the method for adjusting the active power output of the power grid at the sending end by using the thermal power generating unit and the wind power generating unit comprises the following steps:

analyzing the adjusting capacity of a thermal power generating unit in a power grid containing a high-proportion wind power transmission end to obtain the maximum adjustable active power delta P of the thermal power generating unit_gmax；

If Pacl is less than or equal to P_ac-ΔP_gmaxAnd reducing the output of the active power of the power grid containing a high-proportion wind power transmission end through frequency modulation control of a thermal power generating unit, wherein P is_aclIndicating the power transmission limit, P, of an AC transmission system_acRepresenting the active transmission quantity of the alternating current transmission system;

if Pacl > P_ac-ΔP_gmaxAnd under the condition of not cutting off the machine, the active power output of a power grid containing a high-proportion wind power transmission end is reduced by respectively adopting a thermal power generating unit frequency modulation control method and a wind power generating unit active power control method.

Further, the wind turbine generator active power control method comprises a wind turbine generator active acceleration control method and a fan pitch angle active control method.

Further, if Pacl > P_ac-ΔP_gmaxUnder the condition of not cutting off the machine, when the mechanical angular speed of the wind wheel is less than the maximum rotating speed w of the fan_MmaxIn the process, the active power output of a power grid containing a high-proportion wind power transmission end is reduced by respectively adopting a thermal power generating unit frequency modulation control method and a wind power generating unit active acceleration control method; when the wind turbine generator accelerates to the maximum rotating speed w of the fan_MmaxAnd then, if the active power output of the power grid at the transmitting end does not meet the active requirement for reducing the overload risk of the alternating current line, reducing the active power output of the power grid at the transmitting end containing high proportion of wind power by adopting a wind turbine pitch angle active control method on the basis of a frequency modulation control method and a wind turbine active acceleration control method of the thermal power generating unit, and obtaining a coordination control strategy.

Further, the active acceleration control method of the wind turbine generator comprises the following steps:

the mechanical angular speed of the wind wheel when the wind turbine generator works normally is set as w_MUnder the condition of no cutting machine, the mechanical angular speed of the wind wheel is controlled to be w_MAccelerated to w'_MiChanging the coefficient of wind energy utilization C_pAnd further reducing the active power output of the wind turbine, wherein w_M＜w'_Mi≤w_Mmax，w_MmaxMaximum wind wheel mechanical angular velocity;

the active power output reduced by actively accelerating the mechanical angular speed of the wind wheel is as follows:

wherein, Δ P_wiRepresenting the reduced active power output, P, of the wind turbine after actively accelerating the mechanical angular speed of the wind turbine_wiRepresenting active power output, P 'of the wind turbine generator set during normal operation'_wiRepresenting that the mechanical angular speed of the wind wheel is accelerated to w'_MiThe active power output later, rho is the air density, S is the area of one circle swept by the fan blade, C_pmaxIs the maximum wind energy utilization coefficient, C 'of the wind turbine generator set'_pAccelerating mechanical angular speed of wind wheel to w'_MiAnd v is the input wind speed of the fan.

Further, C'_pThe expression of (a) is as follows:

wherein, beta_wAnd E is a natural index, and R is the radius of the fan blade.

Further, the active control method for the pitch angle of the wind turbine comprises the following steps:

the blade arranged on the hub is controlled to adjust the pitch angle, the aerodynamic characteristics of the fan blade are changed, and then the active power output by the wind power plant is adjusted by changing the stress conditions of the blade and the whole machine.

The following advantages can be obtained by adopting the technical means:

the invention provides a power coordination control method of an alternating current-direct current series-parallel system for inhibiting direct current continuous commutation failure. Meanwhile, by analyzing the power flow distribution characteristic of the alternating current-direct current parallel serial transmission system containing high-proportion wind power and the adjusting capacity of the thermal power generating unit, according to the overload condition of the alternating current line, the thermal power generating unit is used for power control under the condition of not cutting off a machine, the active output of the power grid wind power generating unit at the transmission end is actively controlled, and particularly, the mode of actively accelerating the fan and controlling the pitch angle is adopted, so that the overload phenomenon hazard of the alternating current transmission system can be effectively reduced, and the power coordination optimization control of the system is realized.

The method can inhibit the direct current continuous commutation failure, reduce the overload risk of the alternating current transmission system, and effectively ensure the initiative, effectiveness, flexibility, rapidness and economy of the power coordination control of the alternating current and direct current hybrid system of the power grid containing the high-proportion wind power transmission end.

Drawings

FIG. 1 is a flowchart illustrating steps of a power coordination control method for an AC/DC hybrid system for suppressing DC continuous commutation failure according to the present invention;

FIG. 2 is a schematic structural diagram of an AC/DC hybrid delivery system containing high-proportion wind power in the embodiment of the invention;

FIG. 3 is an equivalent circuit diagram of the AC/DC hybrid system according to the embodiment of the present invention;

FIG. 4 is a schematic diagram of a power control strategy of a wind power host in an embodiment of the present invention;

FIG. 5 is a schematic diagram of an active acceleration control method for a wind turbine generator according to an embodiment of the present invention;

FIG. 6 is a graph of an active power output of a wind turbine generator during normal operation of the system in the embodiment of the present invention;

FIG. 7 is a diagram of the active transmission curve of the DC line during normal operation of the system in the embodiment of the present invention;

fig. 8 is a graph of ac line active power transmission curves during normal operation of the system in the embodiment of the present invention;

FIG. 9 is a graph of the extinction angle of the inverter side during normal operation of the system according to the embodiment of the present invention;

FIG. 10 is a graph showing an active power output of a wind turbine generator under different control methods after a system fault according to an embodiment of the present invention;

fig. 11 is a graph of active power transmission curves of the dc lines according to different control methods after a system fault according to the embodiment of the present invention;

fig. 12 is a graph illustrating active power transmission curves of ac lines according to different control methods after a system failure according to an embodiment of the present invention;

fig. 13 is a graph of the arc-quenching angle of the inverter side under different control methods after the system fails according to the embodiment of the invention.

Detailed Description

The technical scheme of the invention is further explained by combining the accompanying drawings as follows:

aiming at the problem of insufficient power coordination control of an alternating current-direct current hybrid system containing a high-proportion wind power transmission end power grid when direct current continuous commutation fails, the invention provides a power coordination control method of the alternating current-direct current hybrid system for inhibiting the direct current continuous commutation failure, which mainly comprises a method for inhibiting the direct current continuous commutation failure and a method for reducing the overload risk of an alternating current transmission system, and as shown in figure 1, the method specifically comprises the following steps:

and step A, after the direct current phase commutation failure of the direct current transmission system occurs, reducing the active power of the direct current transmission system through the direct current instruction at the inversion side, and restraining the direct current continuous phase commutation failure.

And step B, after the direct current phase conversion failure occurs in the direct current transmission system, carrying out overload risk judgment on the alternating current transmission system in the alternating current and direct current parallel-serial system according to the power flow change of the alternating current and direct current parallel-serial system containing the high-proportion wind power transmission end power grid.

And C, regulating the output of the active power of the power grid at the sending end by using the thermal power generating unit and the wind power generating unit to reduce the overload risk of the alternating current transmission system if the alternating current transmission system has the overload risk according to the overload risk judgment result.

In the embodiment of the present invention, the structure of the alternating current/direct current hybrid transmission system including high-proportion wind power is as shown in fig. 2, and based on the alternating current/direct current hybrid transmission system, a relational expression between active power transmission and reactive power consumption of the direct current transmission system is obtained:

wherein Q is_dcRepresenting reactive power, P, of a DC transmission system_dcThe active power of the direct current transmission system is shown, phi represents the power factor of the direct current transmission system, gamma is the extinction angle of the converter valve on the inversion side of the direct current transmission system, and beta is the advanced trigger angle. In step a, the more reactive power is absorbed by the dc transmission system in the recovery stage after the phase change failure, the larger the amplitude of the secondary drop of the inverter side bus voltage is. Therefore, when the system has a greater risk of continuous phase change failure, the reactive power required when the direct current is recovered to a normal state for operation is reduced, namely the amplitude of voltage drop can be reduced, and the continuous phase change failure is effectively inhibited.

According to the formula (5), the active transmission power and the reactive power of the direct current transmission system are in direct proportion, so that after the inversion side of the direct current transmission system fails to perform phase change for the first time, the direct current instruction of the inversion side is immediately generated according to the active power of the current direct current inversion side, the active power of the direct current transmission system is reduced through the direct current instruction of the inversion side, the reactive demand during the direct current phase change failure is effectively reduced, the reactive demand of the direct current transmission system during the direct current phase change failure is further reduced, and the direct current continuous phase change failure is restrained.

If the power grid at the sending end cannot be adjusted in time, the falling active part of the direct current transmission system is transmitted to an adjacent alternating current connecting line, so that the alternating current transmission system of the alternating current-direct current hybrid system containing a high-proportion wind power sending end power grid has a power impact phenomenon, and the alternating current transmission system faces the damage of overload.

The specific operation of step B of the method of the invention is as follows:

and step B01, after the phase conversion of the direct current transmission system fails, large-scale tidal current fluctuation of the alternating current and direct current transmission system is caused, and the tidal current change of the alternating current and direct current transmission system of the power grid containing the high-proportion wind power transmission end is analyzed in real time.

In an embodiment of the invention, the equivalent circuit of the AC transmission system is shown in FIG. 3, where δ₁To the generator terminal voltage E_qAnd system B bus voltage U₂Phase angle difference between them, U₂∠0，U₁For transmitting side AC system voltage, U₁∠0，X_dIs a direct-axis reactance of the generator, X_T1And X_T2For equivalent reactance, X, of transformers on both sides of AC line in AC transmission system_LIs the reactance of an AC line in an AC transmission system.

The power expression of a balance point of an alternating current and direct current series-parallel power transmission system model of an equivalent circuit based on an alternating current transmission system is as follows:

wherein E is_qIs the generator terminal voltage, theta is U₁And U₂The phase angle between.

The active power drop value after the continuous commutation failure of the direct current transmission system meets the following expression:

wherein, Δ P_dcAmplitude, Δ P, representing the active power dip of a DC transmission system_eRepresenting the variation of the active output of the transmitting grid, E_qTo the generator terminal voltage, U₂For AC system B bus voltage, U₁Is the voltage of the transmitting-end power grid, theta is U₁And U₂Phase angle between, Δ U₁Is the change of the voltage of the sending end system, delta₁Is E_qAnd U₂Phase angle difference between them, X_dIs a direct-axis reactance of the generator, X_T1And X_T2Respectively equivalent reactance, delta, of transformers on two sides of an AC line in an AC transmission system₁The delta theta is the power angle variation of the direct current transmission system during fault and is U₁And U₂Amount of phase angle change between, X_LIs the reactance of an AC line in an AC transmission system.

Step B02, based on the tidal current change analysis condition, when the direct current commutation failure occurs in the alternating current and direct current transmission system containing the high-proportion wind power transmission end power grid, the power transmission limit of the alternating current transmission line is made to be P_aclThe power transmission limit increment is delta P_aclReal-time active transmission P of AC transmission system_acAbove the power transmission limit P of an AC transmission line_aclAnd judging that the overload phenomenon occurs in the alternating current transmission system.

Step B03, based on the tidal current change analysis condition, in the alternating current and direct current transmission system containing the high-proportion wind power transmission end power grid, when the inversion side commutation failure of the direct current transmission system causes the active power of the direct current transmission system to fall, if delta P_dc＞ΔP_aclAnd judging that the alternating current transmission system has overload risk.

In the embodiment of the present invention, the relationship between the power angles of the ac transmission system is as follows:

wherein, P_acRepresenting the active transmission quantity, Δ P, of an AC transmission system_acRepresents the power variation of the DC transmission system in fault, K is the slope, and delta f_acIs the frequency variation of the AC transmission system.

According to the formulas (8) and (9), when the alternating current transmission system has overload risk or overload phenomenon, the overload hazard of the alternating current transmission system can be effectively reduced by adjusting the active power output of the power grid at the sending end.

When the system tide is transferred greatly due to the failure of direct current continuous commutation, a thermal power generating unit can be adopted to control the power of a power grid at a transmitting end; in a sending-end power grid containing a high-proportion wind turbine generator, the frequency modulation capacity of a traditional thermal power unit is limited, a load cutting and load cutting mode is generally adopted under the condition that the regulation active capacity of the thermal power unit is insufficient, the problem of overload of an alternating current transmission system is solved, but the mode is conservative, and the advantage of new energy power regulation cannot be fully played. The method of the invention provides a power coordination control strategy under two states of transient state and steady state without switching off, adjusts the power of an alternating current transmission system through a wind turbine generator main machine power control strategy, reduces the overload phenomenon of an alternating current connecting line, and particularly adjusts the active output of a wind power plant group through two methods of fan active acceleration and pitch angle control so as to participate in the power adjustment of an alternating current and direct current hybrid system, as shown in figure 4.

In the embodiment of the present invention, the specific operation of step C is as follows:

step C01, if the alternating current transmission system has overload risk, analyzing the adjusting capacity of the thermal power generating unit in the power grid containing the high-proportion wind power transmission end to obtain the maximum adjustable active power delta P of the thermal power generating unit_gmax。

Step C02, setting the power transmission limit of the AC transmission system as P_aclThe power transmission limit increment is delta P_aclThe adjustable active power of the thermal power generating unit is delta P_g. If the AC transmission system satisfies P_acl≤P_ac-ΔP_gmaxStarting the frequency modulation control of the thermal power generating unit, and reducing the active power output delta P of the power grid containing the high-proportion wind power transmission end_gAnd the overload hazard of the direct current continuous commutation failure to the transient state and the steady state of the alternating current transmission system can be effectively reduced under the condition of not cutting off the load.

Step C03, if the regulating active capacity of the thermal power generating unit is insufficient, P is_acl＞P_ac-ΔP_gmaxIn the conventional control method, a load cutting method is adopted, but the method has the problem of excessive cutting, which increases the number of unnecessary starting and stopping times of the thermal power generating unit and deteriorates the running state of the wind generating unit.

In order to avoid the problems, the method of the invention reduces the active power output of the power grid containing a high proportion of wind power transmission ends through the frequency modulation control of the thermal power generating unit and the active power control method of the wind power generating unit under the condition of not switching off the generator, and on one hand, reduces the delta P through the frequency modulation control of the thermal power generating unit_gmaxOn the other hand, the active power output of a power grid containing a high-proportion wind power transmission end is further reduced by adopting an active power control method of the wind turbine generator set, so that the overload phenomenon of an alternating current transmission system in the transient and steady processes is avoided.

The wind turbine generator active power control method further comprises a wind turbine generator active acceleration control method and a fan pitch angle active control method. If P_acl＞P_ac-ΔP_gmaxUnder the condition of not cutting off the machine, when the mechanical angular speed of the wind wheel is less than the maximum rotating speed w of the fan_MmaxIn the process, the active power output of a power grid containing a high-proportion wind power transmission end is reduced by respectively adopting a thermal power generating unit frequency modulation control method and a wind power generating unit active acceleration control method; when the wind turbine generator accelerates to the maximum rotating speed w of the fan_MmaxAnd then, if the active power output of the power grid at the transmitting end does not meet the active requirement for reducing the overload risk of the alternating current line, reducing the active power output of the power grid at the transmitting end containing high proportion of wind power by adopting a wind turbine pitch angle active control method on the basis of a frequency modulation control method and a wind turbine active acceleration control method of the thermal power generating unit, and obtaining a coordination control strategy.

The active acceleration control method of the wind turbine generator comprises the following specific operations:

when the fan is in a normal working state, the MPPT working mode is adopted, namely the fan works at the position with the highest wind energy utilization coefficient, and the mechanical angular speed of the wind wheel at the moment is set as w_MUnder the condition of no cutting machine, as shown in figure 5, the angular speed of the wind turbine is made to be w_MAccelerated to w'_MiThe fan begins to deviate from the optimum tip speed ratio lambda_optAnd down to λ'_optCan change the wind energy utilization coefficient C_pAnd further reducing the active power output of the wind turbine, wherein w_M＜w'_Mi≤w_Mmax，w_MmaxThe maximum wind turbine mechanical angular velocity.

The active power output reduced by actively accelerating the mechanical angular speed of the wind wheel is as follows:

wherein, Δ P_wiRepresenting the reduced active power output, P, of the wind turbine after actively accelerating the mechanical angular speed of the wind turbine_wiRepresenting active power output, P 'of the wind turbine generator set during normal operation'_wiRepresenting that the mechanical angular speed of the wind wheel is accelerated to w'_MiThe active power output later, rho is the air density, S is the area of one circle swept by the fan blade, C_pmaxIs the maximum wind energy utilization coefficient, C 'of the wind turbine generator set'_pAccelerating mechanical angular speed of wind wheel to w'_MiAnd v is the input wind speed of the fan.

C′_pThe expression of (a) is as follows:

wherein, beta_wAnd E is a natural index, and R is the radius of the fan blade.

The active control method for the pitch angle of the fan comprises the following specific operations:

the blade arranged on the hub is controlled to adjust the size of the pitch angle, so that the aerodynamic characteristics of the fan blade are changed, the active power output by the wind power plant is adjusted by changing the stress conditions of the blade and the whole machine, and the purposes of improving the stress conditions of the blade and the whole machine and adjusting the output power and keeping the output power stable at high wind speed are achieved.

The invention adopts a continuous commutation failure suppression method based on the reactive power requirement of an improvement system, a commutation failure trend analysis and control method and a wind power active participation commutation failure power coordination control method. According to the continuous commutation failure occurrence risk degree, the active power of a transmission system is reduced by adjusting the direct current instruction of the inversion side, and the reactive demand of the system is improved, so that the direct current continuous commutation failure is restrained; the commutation failure power flow analysis and control method can judge whether to adopt a generator tripping load or wind power active power control strategy to carry out coordination control on the AC/DC transmission system by analyzing the overload capacity of the AC transmission system and the regulating capacity of the thermal power plant; the power coordination control method for the failure of the active participation of wind power in commutation reduces the active output of a power grid at a sending end by adopting a method of actively accelerating and reducing the power of a fan, and can adjust the power grid at the sending end by adopting a pitch angle control method if the rotating speed reaches the maximum rotating speed of the fan.

In order to verify the effect of the present invention, the following experiment is given in the embodiment of the present invention:

building a wind-fire bundling alternating-current and direct-current hybrid delivery system model shown in fig. 2 in an electromagnetic transient simulation software PSCAD, wherein the rated capacity of a wind turbine generator set is 1800MW, and the rated capacity of a thermal power generator set is 1200 MW; the voltage class of the high-voltage alternating-current line is 330kV, and the rated capacity is 1600 MW; the voltage grade of the LCC type high-voltage direct-current line is 500kV, and the rated capacity is 1000 MW. When the high-proportion wind power alternating current-direct current hybrid transmission system normally operates, the wind speed of a wind power plant is 13m/s, a relevant electric quantity curve in the system is shown in fig. 6-9, the active power output of a wind power unit is 1240MW, the active transmission of a direct current line is 960MW, the active transmission of the alternating current line is 1300MW, and the extinction angle of the inversion side of the direct current line is kept at the same value.

When a current conversion bus on an inversion side of a direct current transmission system is set to be in a 1s state, a three-phase grounding fault occurs, the fault duration time is 0.05s, direct current phase conversion failure occurs on the inversion side of the direct current transmission system, and the direct current continuous phase conversion failure is inhibited through the following 3 methods respectively:

the control method 1 comprises the following steps: and (5) adopting a CIGRE standard test model for control.

The control method 2 comprises the following steps: by adjusting the direct current instruction of the inversion side, the active power transmission size of the direct current transmission system is reduced, and the reactive power requirement of the system is reduced.

The control method 3: on the basis of the control method 2, the active power control method of the wind turbine generator is adopted to reduce the active output of the power grid at the transmitting end, namely the method provided by the invention.

Simulation curves of the electrical quantities in the system after the 3 control methods are adopted are shown in fig. 10-13.

When the control method 1 is adopted, as can be seen from fig. 11, under the condition that the active power output of the wind turbine generator remains unchanged, the extinction angle falls to 1.5 degrees twice continuously, it can be judged that the system has continuous commutation failure, the active power of the direct current transmission system falls to 450MW twice continuously, meanwhile, the alternating current transmission system has twice transient overload, the peak value reaches 1520MW, and the system recovers the steady-state operation in 1.35 s.

When the control method 2 is adopted, the data acquisition needs 20ms, so that after the initial commutation failure occurs for 20ms, the reactive power requirement of the direct current transmission system can be reduced by adopting the control method 2, and the continuous commutation failure is effectively avoided. However, the active power output of the sending-end power grid is not changed, the active power of the direct current transmission system is reduced, and the alternating current transmission system inevitably has a relatively obvious overload phenomenon in both the transient state and the steady state, wherein the peak value of the transient overload is similar to the peak value of the overload phenomenon adopting the control method 1, but the steady state active power of the alternating current transmission system is increased by 8% after the direct current continuous commutation failure is inhibited due to the adjustment of the direct current transmission active power, and the alternating current transmission system is in an overload state for a long time, as shown in fig. 12, the system has a trip risk.

When the control method 3 is adopted, the risk of overload phenomenon of the alternating current transmission line can be reduced while the direct current continuous commutation failure is restrained. After 20ms of first commutation failure of the inversion side is detected, active acceleration control and active pitch angle control of the fan are performed, the wind turbine generator is no longer in the MPPT output working mode, and the active output of the wind power plant is obviously reduced, as shown in FIG. 13. By adopting the method, the overload phenomenon of the steady-state active power of the alternating current transmission system after the suppression of the direct current continuous commutation failure is eliminated, the alternating current transmission system is recovered to a normal operation state, the peak value of the active power impact on the alternating current transmission system during the commutation failure is reduced to be within 1400MW from 1520MW, and the possibility of the occurrence of faults such as tripping and the like in the system is effectively reduced.

According to the method, after the phase commutation failure occurs in the direct current transmission system, the direct current transmission power is adjusted in time by adjusting the direct current instruction of the inversion side, so that the direct current continuous phase commutation failure is effectively inhibited; meanwhile, the invention can also respectively use the thermal power generating unit and the wind power generating unit to reduce the active power output of the power grid at the sending end under the condition of not cutting off the machine, and reduce the damage of the overload phenomenon of the alternating current transmission system so as to realize the power coordination optimization control of the system. The method can inhibit the direct current continuous commutation failure, reduce the overload risk of the alternating current transmission system, and effectively ensure the initiative, effectiveness, flexibility, rapidness and economy of the power coordination control of the alternating current and direct current hybrid system of the power grid containing the high-proportion wind power transmission end.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.