阅读说明：本技术 一种双馈风机等效惯量评估方法及系统 (Doubly-fed fan equivalent inertia evaluation method and system ) 是由 王康 李立 张青蕾 乔彦君 邢其鹏 王彤 邓俊 彭书涛 夏楠 于 2021-08-20 设计创作，主要内容包括：本发明涉及一种双馈风机等效惯量评估方法及系统。所述方法包括获取稳态信息,所述稳态信息包括双馈风机的输出功率和电网频率；根据所述双馈风机的输出功率计算初始转子角速度；根据所述电网频率计算系统初始同步角速度；基于所述系统初始同步角速度和所述初始转子角速度计算等效惯性时间常数,所述等效惯性时间常数用于评估双馈风机等效惯量。本发明在计算等效惯性时间常数时过程简单、计算量小,能够提高惯量评估的准确性。(The invention relates to an equivalent inertia evaluation method and system for a double-fed fan. The method comprises the steps of obtaining steady state information, wherein the steady state information comprises the output power and the power grid frequency of the double-fed fan; calculating the initial rotor angular speed according to the output power of the doubly-fed fan; calculating the initial synchronous angular speed of the system according to the power grid frequency; and calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, wherein the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed fan. The method has the advantages of simple process and small calculation amount when calculating the equivalent inertia time constant, and can improve the accuracy of inertia evaluation.)

1. The method for evaluating the equivalent inertia of the doubly-fed wind turbine is characterized by comprising the following steps of:

acquiring steady state information, wherein the steady state information comprises the output power and the power grid frequency of the doubly-fed wind turbine;

calculating the initial rotor angular speed according to the output power of the doubly-fed fan;

calculating the initial synchronous angular speed of the system according to the power grid frequency;

and calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, wherein the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed fan.

2. The doubly-fed wind turbine equivalent inertia evaluation method according to claim 1, wherein the calculating an equivalent inertia time constant based on the system initial synchronous angular velocity and the initial rotor angular velocity specifically comprises:

acquiring parameters of the doubly-fed wind turbine, wherein the parameters of the doubly-fed wind turbine comprise: the method comprises the following steps of (1) obtaining a gain parameter, a frequency domain differential operator, a time constant of a filter, an inherent inertia time constant of the doubly-fed fan and a rated angular speed of the doubly-fed fan;

and calculating an equivalent inertia time constant according to the parameters of the doubly-fed fan, the initial synchronous angular speed of the system and the initial rotor angular speed.

3. The doubly-fed wind turbine equivalent inertia evaluation method according to claim 2, wherein the calculating an equivalent inertia time constant according to the doubly-fed wind turbine parameters, the system initial synchronous angular velocity and the initial rotor angular velocity specifically comprises:

according to solving formulaCalculating an equivalent inertia time constant, wherein H_eqRepresents the equivalent time constant of inertia, K_dvicDifferential gain representing virtual inertia control, s represents frequency domain differential operator, K_pvicProportional gain, T, representing virtual inertia control_fRepresenting the time constant of the filter, K_{p_pll}Indicating the proportional gain, K, of the phase-locked loop_{i_pll}Representing the integral gain, omega, of a phase-locked loop_r0Representing the initial rotor angular velocity, ω_s0Representing the initial synchronous angular velocity of the system, H_dRepresenting the inherent inertia time constant, K, of the doubly-fed wind turbine_psIndicating the proportional gain, K, of the speed controller_isIndicating the integral gain, omega, of the speed controller_NRepresenting the rated angular speed of the doubly-fed fan.

4. The doubly-fed wind turbine equivalent inertia evaluation method according to claim 3, wherein the determination method for solving the formula is as follows:

determining a relational expression according to the rotating speed reference value and the active power output by the double-fed fan;

establishing a proportional differential virtual inertia control model based on the frequency of a phase-locked loop by taking the stator voltage phase angle increment as input and the electromagnetic torque reference value increment provided by virtual inertia control as output;

constructing a maximum power tracking model of the doubly-fed wind turbine by taking the electromagnetic power of the doubly-fed wind turbine as input and the reference value increment of the electromagnetic torque as output;

constructing a generator transient model of the doubly-fed wind turbine by taking the electromagnetic torque reference value as input and the rotating speed of a rotor of the doubly-fed wind turbine as output;

determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression; the first kinetic energy variation expression is a kinetic energy variation expression in the doubly-fed fan inertia response process before the additional virtual inertia control, and the second kinetic energy variation expression is a kinetic energy variation in the doubly-fed fan inertia response process after the additional virtual inertia control;

and determining the solving formula according to a three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the maximum power tracking model generator transient model of the doubly-fed wind turbine and the equivalent inertia time expression.

5. The doubly-fed wind turbine equivalent inertia evaluation method according to claim 4, wherein the determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression specifically comprises:

determining a virtual rotational inertia expression according to the first kinetic energy variation expression and the second kinetic energy variation expression;

and determining an equivalent inertia time constant expression based on the virtual moment of inertia expression.

6. The equivalent inertia evaluation system of the doubly-fed wind turbine is characterized by comprising the following components:

the acquiring module is used for acquiring steady state information, wherein the steady state information comprises the output power and the power grid frequency of the double-fed fan;

the initial rotor angular speed determining module is used for calculating the initial rotor angular speed according to the output power of the doubly-fed fan;

the system initial synchronization angular velocity determining module is used for calculating the system initial synchronization angular velocity according to the power grid frequency;

and the equivalent inertia time constant determination module is used for calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, and the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed fan.

7. The doubly-fed wind turbine equivalent inertia evaluation system of claim 6, wherein the equivalent inertia time constant determination module specifically comprises:

the obtaining submodule is used for obtaining parameters of the doubly-fed wind turbine, and the parameters of the doubly-fed wind turbine comprise: the method comprises the following steps of (1) obtaining a gain parameter, a frequency domain differential operator, a time constant of a filter, an inherent inertia time constant of the doubly-fed fan and a rated angular speed of the doubly-fed fan;

and the equivalent inertia time constant determination submodule is used for calculating an equivalent inertia time constant according to the doubly-fed fan parameter, the system initial synchronous angular speed and the initial rotor angular speed.

8. The doubly-fed wind turbine equivalent inertia evaluation system of claim 7, wherein the equivalent inertia time constant determination submodule specifically comprises:

a solving unit for solving the formula

Calculating an equivalent inertia time constant, wherein H_eqRepresents the equivalent time constant of inertia, K_dvicDifferential gain representing virtual inertia control, s represents frequency domain differential operator, K_pvicProportional gain, T, representing virtual inertia control_fRepresenting the time constant of the filter, K_{p_pll}Indicating the proportional gain, K, of the phase-locked loop_{i_pll}Representing the integral gain, omega, of a phase-locked loop_r0Representing the initial rotor angular velocity, ω_s0Representing the initial synchronous angular velocity of the system, H_dRepresenting the inherent inertia time constant, K, of the doubly-fed wind turbine_psIndicating the proportional gain, K, of the speed controller_isIndicating the integral gain, omega, of the speed controller_NRepresenting the rated angular speed of the doubly-fed fan.

9. The doubly-fed wind turbine equivalent inertia evaluation system of claim 8, further comprising:

the relational expression determining module is used for determining a relational expression according to the rotating speed reference value and the active power output by the double-fed fan;

the first model building module is used for building a proportional differential virtual inertia control model based on the frequency of a phase-locked loop by taking the stator voltage phase angle increment as input and the electromagnetic torque reference value increment provided by virtual inertia control as output;

the second model building module is used for building a maximum power tracking model of the doubly-fed wind turbine by taking the electromagnetic power of the doubly-fed wind turbine as input and the reference value increment of the electromagnetic torque as output;

the third model building module is used for building a generator transient model of the doubly-fed wind turbine by taking the electromagnetic torque reference value as input and the rotating speed of the rotor of the doubly-fed wind turbine as output;

the equivalent inertia time constant expression determining module is used for determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression; the first kinetic energy variation expression is a kinetic energy variation expression in the doubly-fed fan inertia response process before the additional virtual inertia control, and the second kinetic energy variation expression is a kinetic energy variation in the doubly-fed fan inertia response process after the additional virtual inertia control;

and the solving formula determining module is used for determining the solving formula according to a three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the generator transient model of the maximum power tracking model of the doubly-fed wind turbine and the equivalent inertia time expression.

10. The doubly-fed wind turbine equivalent inertia evaluation system of claim 9, wherein the equivalent inertia time constant expression determining module specifically includes:

a virtual moment of inertia expression determining submodule, configured to determine a virtual moment of inertia expression according to the first kinetic energy variation expression and the second kinetic energy variation expression;

and the equivalent inertia time constant expression determining submodule is used for determining an equivalent inertia time constant expression based on the virtual rotation inertia expression.

Technical Field

The invention relates to the field of evaluation, in particular to a method and a system for evaluating equivalent inertia of a doubly-fed fan.

Background

Under the background of the era of carbon peak reaching and carbon neutralization, accelerating the construction of a novel power system taking new energy as a main body is a necessary way of the power industry. High proportions of renewable energy sources and high proportions of power electronics are becoming important trends and key features of power system development. As a main model of a wind power market, the double-fed fan has the characteristics of flexibility and rapidness in control, so that the kinetic energy of a rotor and the output active power of the double-fed fan are relatively decoupled, and the double-fed fan basically has no inertia supporting capacity. With the increase of the permeability of the wind turbine generator, the integral inertia level of the power system is inevitably weakened, and the disturbance rejection capability and the stability characteristic of the system are seriously deteriorated. In order to ensure safe and stable operation of a power grid, a virtual inertia control technology becomes an important means for improving the inertia level of a power system, the related quantity of power grid frequency deviation is introduced into the active control link of a converter on the basis of the traditional control strategy of a double-fed fan, the power grid frequency fluctuation is resisted by absorbing or releasing rotor kinetic energy, and then inertia support is provided for the power grid.

In general, the equivalent inertia time constant of the synchronous machine set is given, and the value of the equivalent inertia time constant is basically not changed. However, for the double-fed wind turbine, the inertia response characteristic of the double-fed wind turbine is closely related to the type of a converter, the control mode and the operation condition of a unit. The strong randomness, the intermittence and the fluctuation of the output of the double-fed fan enable the operation mode of the system to be complex and changeable, and the system inertia shows larger fluctuation characteristics in time scale, so that after the double-fed fan with virtual inertia control is connected into a power grid, the system inertia is no longer the inherent characteristics which cannot be changed, the time-space change characteristics of the system inertia are more prominent, and the inertia response process after disturbance is more complex and changeable. The inertia evaluation can provide scientific reference for power grid planning and dispatching operation, and is helpful for power grid operation dispatchers to master the equivalent inertia level of the current system, identify weak inertia periods, nodes or areas, and further take local inertia compensation measures in a targeted manner, so as to provide a basis for refined inertia regulation and control.

The transient stability and transient instability modes of the system are not only related to the total inertia of the system, but also more related to the distribution of the inertia of the whole system. However, most of the existing inertia evaluation methods focus on the equivalent inertia of the whole system, and a relevant theoretical method is currently lacked in relation to the research on the inertia and the response characteristics of the doubly-fed wind turbine. The most common calculation method for inertia evaluation is to calculate an inertia time constant by using a swing equation, and the method needs to accurately measure and calculate the frequency change rate according to a frequency curve, and has large calculation amount and high complexity. Both the filtering value of the frequency change rate and the determination of the disturbance occurrence time bring difficulty to calculation, and the accuracy of inertia evaluation is influenced when the calculation is wrong. In addition, the method depends on time series measurement data under power grid disturbance, and real-time continuous monitoring of system inertia under normalization cannot be realized.

Disclosure of Invention

The invention aims to provide an equivalent inertia evaluation method and system for a double-fed fan, which are simple in process and small in calculated amount when an equivalent inertia time constant is calculated, and can improve the accuracy of inertia evaluation.

In order to achieve the purpose, the invention provides the following scheme:

a doubly-fed wind turbine equivalent inertia evaluation method comprises the following steps:

acquiring steady state information, wherein the steady state information comprises the output power and the power grid frequency of the doubly-fed wind turbine;

calculating the initial rotor angular speed according to the output power of the doubly-fed fan;

calculating the initial synchronous angular speed of the system according to the power grid frequency;

and calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, wherein the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed fan.

Optionally, the calculating an equivalent inertia time constant based on the system initial synchronous angular velocity and the initial rotor angular velocity specifically includes:

acquiring parameters of the doubly-fed wind turbine, wherein the parameters of the doubly-fed wind turbine comprise: the method comprises the following steps of (1) obtaining a gain parameter, a frequency domain differential operator, a time constant of a filter, an inherent inertia time constant of the doubly-fed fan and a rated angular speed of the doubly-fed fan;

and calculating an equivalent inertia time constant according to the parameters of the doubly-fed fan, the initial synchronous angular speed of the system and the initial rotor angular speed.

Optionally, calculating an equivalent inertia time constant according to the doubly-fed wind turbine parameter, the system initial synchronous angular velocity, and the initial rotor angular velocity, specifically:

according to solving formulaCalculating an equivalent inertia time constant, wherein H_eqRepresents the equivalent time constant of inertia, K_dvicDifferential gain representing virtual inertia control, s represents frequency domain differential operator, K_pvicProportional gain, T, representing virtual inertia control_fRepresenting the time constant of the filter, K_{p_pll}Indicating the proportional gain, K, of the phase-locked loop_{i_pll}Representing the integral gain, omega, of a phase-locked loop_r0Representing the initial rotor angular velocity, ω_s0Representing the initial synchronous angular velocity of the system, H_dRepresenting the inherent inertia time constant, K, of the doubly-fed wind turbine_psIndicating the proportional gain, K, of the speed controller_isIndicating the integral gain, omega, of the speed controller_NRepresenting the rated angular speed of the doubly-fed fan.

Optionally, the determining method of the solution formula includes:

determining a relational expression according to the rotating speed reference value and the active power output by the double-fed fan;

establishing a proportional differential virtual inertia control model based on the frequency of a phase-locked loop by taking the stator voltage phase angle increment as input and the electromagnetic torque reference value increment provided by virtual inertia control as output;

constructing a maximum power tracking model of the doubly-fed wind turbine by taking the electromagnetic power of the doubly-fed wind turbine as input and the reference value increment of the electromagnetic torque as output;

constructing a generator transient model of the doubly-fed wind turbine by taking the electromagnetic torque reference value as input and the rotating speed of a rotor of the doubly-fed wind turbine as output;

determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression; the first kinetic energy variation expression is a kinetic energy variation expression in the doubly-fed fan inertia response process before the additional virtual inertia control, and the second kinetic energy variation expression is a kinetic energy variation in the doubly-fed fan inertia response process after the additional virtual inertia control;

and determining the solving formula according to a three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the maximum power tracking model generator transient model of the doubly-fed wind turbine and the equivalent inertia time expression.

Optionally, the determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression specifically includes:

determining a virtual rotational inertia expression according to the first kinetic energy variation expression and the second kinetic energy variation expression;

and determining an equivalent inertia time constant expression based on the virtual moment of inertia expression.

A doubly-fed fan equivalent inertia evaluation system comprises:

the acquiring module is used for acquiring steady state information, wherein the steady state information comprises the output power and the power grid frequency of the double-fed fan;

the initial rotor angular speed determining module is used for calculating the initial rotor angular speed according to the output power of the doubly-fed fan;

the system initial synchronization angular velocity determining module is used for calculating the system initial synchronization angular velocity according to the power grid frequency;

and the equivalent inertia time constant determination module is used for calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, and the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed fan.

Optionally, the equivalent inertia time constant determining module specifically includes:

the obtaining submodule is used for obtaining parameters of the doubly-fed wind turbine, and the parameters of the doubly-fed wind turbine comprise: the method comprises the following steps of (1) obtaining a gain parameter, a frequency domain differential operator, a time constant of a filter, an inherent inertia time constant of the doubly-fed fan and a rated angular speed of the doubly-fed fan;

and the equivalent inertia time constant determination submodule is used for calculating an equivalent inertia time constant according to the doubly-fed fan parameter, the system initial synchronous angular speed and the initial rotor angular speed.

Optionally, the equivalent inertia time constant determining submodule specifically includes:

a solving unit for solving the formula

Calculating an equivalent inertia time constant, wherein H_eqRepresents the equivalent time constant of inertia, K_dvicDifferential gain representing virtual inertia control, s represents frequency domain differential calculationZi, K_pvicProportional gain, T, representing virtual inertia control_fRepresenting the time constant of the filter, K_{p_pll}Indicating the proportional gain, K, of the phase-locked loop_{i_pll}Representing the integral gain, omega, of a phase-locked loop_r0Representing the initial rotor angular velocity, ω_s0Representing the initial synchronous angular velocity of the system, H_dRepresenting the inherent inertia time constant, K, of the doubly-fed wind turbine_psIndicating the proportional gain, K, of the speed controller_isIndicating the integral gain, omega, of the speed controller_NRepresenting the rated angular speed of the doubly-fed fan.

Optionally, the double-fed fan equivalent inertia evaluation system further includes:

the relational expression determining module is used for determining a relational expression according to the rotating speed reference value and the active power output by the double-fed fan;

the first model building module is used for building a proportional differential virtual inertia control model based on the frequency of a phase-locked loop by taking the stator voltage phase angle increment as input and the electromagnetic torque reference value increment provided by virtual inertia control as output;

the second model building module is used for building a maximum power tracking model of the doubly-fed wind turbine by taking the electromagnetic power of the doubly-fed wind turbine as input and the reference value increment of the electromagnetic torque as output;

the third model building module is used for building a generator transient model of the doubly-fed wind turbine by taking the electromagnetic torque reference value as input and the rotating speed of the rotor of the doubly-fed wind turbine as output;

the equivalent inertia time constant expression determining module is used for determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression; the first kinetic energy variation expression is a kinetic energy variation expression in the doubly-fed fan inertia response process before the additional virtual inertia control, and the second kinetic energy variation expression is a kinetic energy variation in the doubly-fed fan inertia response process after the additional virtual inertia control;

and the solving formula determining module is used for determining the solving formula according to a three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the generator transient model of the maximum power tracking model of the doubly-fed wind turbine and the equivalent inertia time expression.

Optionally, the equivalent inertia time constant expression determining module specifically includes:

a virtual moment of inertia expression determining submodule, configured to determine a virtual moment of inertia expression according to the first kinetic energy variation expression and the second kinetic energy variation expression;

and the equivalent inertia time constant expression determining submodule is used for determining an equivalent inertia time constant expression based on the virtual rotation inertia expression.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects: the method comprises the steps of obtaining steady state information, wherein the steady state information comprises the output power and the power grid frequency of the double-fed fan; calculating the initial rotor angular speed according to the output power of the doubly-fed fan; calculating the initial synchronous angular speed of the system according to the power grid frequency; the equivalent inertia time constant is calculated based on the system initial synchronous angular speed and the initial rotor angular speed, the equivalent inertia time constant is used for evaluating the equivalent inertia of the double-fed fan, the initial rotor angular speed and the system initial synchronous angular speed can be obtained according to steady state information, the frequency change rate does not need to be calculated, compared with a calculation method for calculating the inertia time constant by using a swing equation in the background technology, the calculation method is small in calculation amount and free of a complex calculation process, the equivalent inertia of the double-fed fan can be accurately evaluated in real time, scientific reference can be provided for power grid planning and dispatching operation, a power grid operation dispatcher can be helped to master the equivalent inertia level of the current system, a weak period, a node or an area is identified, and further local inertia compensation measures are pertinently taken, and a basis is provided for fine inertia regulation and control.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

Fig. 1 is a flowchart of a doubly-fed wind turbine equivalent inertia evaluation method according to an embodiment of the present invention;

fig. 2 is a structural diagram of an equivalent model of a doubly-fed wind turbine including virtual inertia control in a rotor speed time scale according to an embodiment of the present invention;

fig. 3 is a structural diagram of a proportional-derivative virtual inertia control model based on a phase-locked loop frequency according to an embodiment of the present invention;

fig. 4 is a structural diagram of a maximum power tracking model of a doubly-fed wind turbine provided in an embodiment of the present invention;

fig. 5 is a structural diagram of a generator transient model of a doubly-fed wind turbine provided in an embodiment of the present invention;

FIG. 6 is a block diagram of an improved four-machine two-zone test system provided by an embodiment of the present invention;

FIG. 7 shows that the method is adopted in the doubly-fed wind turbine P_eA comparison result graph of the evaluation value of the equivalent inertia time constant obtained when the equivalent inertia time constant is 0.3 and the true value;

FIG. 8 shows that the method is adopted in the doubly-fed wind turbine P_eA comparison result graph of the evaluation value of the equivalent inertia time constant obtained when the equivalent inertia time constant is 0.6 and the true value;

fig. 9 is a structural diagram of an equivalent inertia evaluation system of a doubly-fed wind turbine provided in an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

The embodiment provides a method for evaluating equivalent inertia of a doubly-fed wind turbine, as shown in fig. 1, the method includes:

step 101: and acquiring steady state information. The steady state information comprises the output power and the power grid frequency of the double-fed fan, and the output power and the power grid frequency of the double-fed fan under the steady state operation.

Step 102: calculating initial rotor angular velocity omega according to the output power of the doubly-fed fan_r0。

Step 103: calculating the initial synchronous angular velocity omega of the system according to the power grid frequency_s0。

Step 104: and calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, wherein the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed fan.

In practical applications, ω_s0The method can be used for obtaining the frequency data of the real-time measurement power grid; initial rotor angular velocity ω of the wind turbine at steady state, irrespective of variations in wind speed_r0Equal to the reference value omega of the rotor speed_r*，ω_rThe numerical value of the equation is related to the real-time wind speed of the wind power plant, and can be obtained according to the expression of the formula (3) which is an optimal power-rotating speed curve in practical application. Therefore, omega is respectively obtained by utilizing the measurement information of the output power and the grid frequency of the doubly-fed wind turbine under the steady-state operation_r0And ω_s0And further evaluating the equivalent inertia of the doubly-fed wind turbine in real time.

In practical application, step 104 specifically includes:

acquiring parameters of the doubly-fed wind turbine, wherein the parameters of the doubly-fed wind turbine comprise: the method comprises the following steps of (1) obtaining a gain parameter, a frequency domain differential operator, a time constant of a filter, an inherent inertia time constant of the doubly-fed fan and a rated angular speed of the doubly-fed fan; the gain parameters include: a differential gain of the virtual inertia control, a proportional gain of the phase locked loop, an integral gain of the phase locked loop, a proportional gain of the speed controller, and an integral gain of the speed controller.

And calculating an equivalent inertia time constant according to the parameters of the doubly-fed fan, the initial synchronous angular speed of the system and the initial rotor angular speed.

In practical application, the parameters of the doubly-fed wind turbine can be obtained according to nameplate data or a technical manual.

In practical application, the calculating an equivalent inertia time constant according to the doubly-fed wind turbine parameter, the system initial synchronous angular velocity and the initial rotor angular velocity specifically comprises:

the equivalent inertia time constant is calculated according to solving equation (14).

In practical application, the determination method of the solution formula comprises the following steps:

and determining a relational expression according to the rotating speed reference value and the active power output by the double-fed fan.

And establishing a proportional differential virtual inertia control model based on the frequency of the phase-locked loop by taking the stator voltage phase angle increment as input and taking the electromagnetic torque reference value increment provided by the virtual inertia control as output.

And constructing a maximum power tracking model of the doubly-fed wind turbine by taking the electromagnetic power of the doubly-fed wind turbine as input and the reference value increment of the electromagnetic torque as output.

And establishing a generator transient model of the doubly-fed wind turbine by taking the electromagnetic torque reference value as input and the rotating speed of the rotor of the doubly-fed wind turbine as output.

Determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression; the first kinetic energy variation expression is a kinetic energy variation expression in the inertia response process of the double-fed fan before the additional virtual inertia control, and the second kinetic energy variation expression is a kinetic energy variation in the inertia response process of the double-fed fan after the additional virtual inertia control.

And determining the solving formula according to a three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the maximum power tracking model generator transient model of the doubly-fed wind turbine and the equivalent inertia time expression.

In practical applications, the determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression specifically includes:

and determining a virtual moment of inertia expression according to the first kinetic energy variation expression and the second kinetic energy variation expression.

And determining an equivalent inertia time constant expression based on the virtual moment of inertia expression.

In practical application, a proportional differential virtual inertia control model based on the frequency of a phase-locked loop, a maximum power tracking model of a doubly-fed wind turbine and a generator transient model of the doubly-fed wind turbine are collectively called as an equivalent model of the doubly-fed wind turbine under the rotor rotation speed time scale with virtual inertia control, and the structure is shown in fig. 2.

The invention adopts a three-phase synchronous phase-locked loop which is widely applied at present, and the dynamic equation of the three-phase synchronous phase-locked loop is as follows:

wherein x is_pllIs the accumulated error when tracking the stator d-axis voltage;is the derivative of the accumulated error in tracking the stator d-axis voltage; u. of_dsIs stator voltage U_sA d-axis component of (a); delta_pllRepresenting a phase angle of the phase-locked loop output;a differential representing a phase angle of the phase-locked loop output; omega_pllAn estimated dq coordinate system rotational angular velocity for the phase locked loop; omega_sSynchronizing the angular speed of rotation for the grid; k_{i_pll}And K_{p_pll}The integral gain of the phase-locked loop and the proportional gain of the phase-locked loop are respectively.

The proportional differential virtual inertia control is to introduce an auxiliary power related to the proportional and differential quantities of the system frequency deviation on the basis of the conventional control of the wind turbine generator. When the system frequency fluctuates, the doubly-fed fan estimates a dq coordinate system through a phase-locked loopAngular velocity of rotation omega_pllTo measure system frequency, the electromagnetic torque reference value increment delta T provided by virtual inertia control_vicThe frequency domain expression (proportional differential virtual inertia control model based on the phase-locked loop frequency) is as follows:

wherein, K_dvicAnd K_pvicDifferential gain of virtual inertia control and proportional gain of virtual inertia control are respectively obtained; t is_fIs the time constant of the filter; Δ ω_pllThe change in angular velocity estimated for the phase-locked loop, s denotes the frequency domain differential operator, Δ δ_sFor stator voltage phase angle delta, according to the above, a proportional differential virtual inertia control model based on the frequency of the phase-locked loop can be obtained as shown in fig. 3, wherein the input is the stator voltage phase angle delta_sAnd outputting the electromagnetic torque reference value increment delta T provided for virtual inertia control_vic。

The maximum power tracking model includes Maximum Power Point Tracking (MPPT) control and a speed controller. In practice, since the average wind speed at the impeller cannot be directly measured, the corresponding rotating speed command value is usually calculated according to the output power of the unit. Output power P of fan_eCalculating a reference value omega of the rotation speed_rThe approximation algorithm (relational expression) is:

when the actually detected rotating speed omega of the rotor of the doubly-fed wind turbine_rSpeed reference value omega obtained by MPPT_rWhen the rotation speed deviation occurs between the motor and the rotor, the rotation speed deviation is used as an input quantity, and the reference value of the electromagnetic torque of the generator is adjusted through the speed controller to help the rotor to recover to the optimal operation state. The transfer function expression of the electromagnetic torque reference value increment delta T under the maximum power tracking model (the maximum power tracking model of the doubly-fed wind turbine) is as follows:

wherein, K_psAnd K_isProportional gain of the speed controller and integral gain of the speed controller respectively; omega_rThe actual rotating speed of the fan. According to the above, a maximum power tracking model of the doubly-fed wind turbine can be obtained as shown in fig. 4, where the input is the electromagnetic power (output power) P of the doubly-fed wind turbine_eAnd the output is the electromagnetic torque reference value increment delta T under the maximum power tracking model.

Wherein the virtual inertia control provides an electromagnetic torque reference value increment delta T_vicThe frequency domain expression (proportional differential virtual inertia control model based on the phase-locked loop frequency) and the transfer function expression (maximum power tracking model of the doubly-fed wind turbine) of the electromagnetic torque reference value increment delta T under the maximum power tracking model can obtain the electromagnetic torque reference value T controlled by the rotor current_e ^*The control of the rotor-side converter is realized by stator voltage orientation vector control, and a stator flux linkage equation and a voltage equation are as follows:

wherein psi_dsAnd psi_qsD-axis stator flux linkage and q-axis stator flux linkage respectively; u. of_dsAnd u_qsRespectively stator voltage U_sThe components on the d-axis and q-axis; x_sIs a stator inductance; x_mThe stator and the rotor are mutually inducted; i.e. i_dsAnd i_drD-axis currents of a stator winding and a rotor winding respectively; i.e. i_qsAnd i_qrQ-axis currents, psi, of stator and rotor windings, respectively_sIs stator flux linkage, U_sIs the stator voltage.

The electromagnetic torque equation for rotor current control is:

wherein, T_eIs an electromagnetic torque; p is the pole pair number of the stator winding, and the upper right corner plus the 'x' represents the command value of each parameter of the fan.

The generator rotor equation of motion is:

T_m-T_e＝2H_dω_r·s (7)

wherein, T_mThe mechanical torque of the double-fed fan is obtained; h_dThe intrinsic inertia time constant of the double-fed fan is obtained; omega_rThe rotating speed of the rotor of the doubly-fed fan is shown.

The generator transient model (equation 6 and equation 7) of the doubly-fed wind turbine is shown in fig. 5, wherein the input is the electromagnetic torque reference value T of the rotor current control_e ^*And the output is the rotor speed omega of the doubly-fed fan_r(obtaining i from the second equation of equation 6)_qr ^*According to i_qr ^*To obtain i_qrAccording to i_qrAnd the first of equation 6 yields T_eAccording to T_eTo obtain omega_r)，k₁＝-2X_s/(3pX_m) And Gq(s) is a current inner loop control link, the response speed of the current inner loop control is far faster than the rotor rotating speed scale, and the rotor current fast tracking command value can be considered to be Gq(s) approximately equal to 1.

In practical application, the first kinetic energy variation expression is that the kinetic energy variation in the doubly-fed wind turbine inertia response process can be represented by the rotor speed variation and the inherent rotational inertia:

wherein, P, S_N，J_DFIG，ω_r0，Δω_rThe method comprises the steps of respectively counting the pole pairs of the doubly-fed fan, the rated capacity, the inherent moment of inertia, the initial rotor angular speed and the rotor angular speed increment.

In practical application, the second kinetic energy variation expression is that after the accessory and the virtual inertia are controlled, the rotating speed of the doubly-fed fan is coupled with the angular speed of the system, and the kinetic energy variation in the inertia response process can be represented by the system synchronous angular speed variation and the virtual rotational inertia:

wherein, J_eq，ω_s0，Δω_sThe method comprises the steps of respectively obtaining the virtual rotational inertia of the doubly-fed wind turbine, the initial synchronous angular velocity of a system and the synchronous angular velocity increment of the system.

In practical application, virtual moment of inertia expression formula

In practical application, an equivalent inertia time constant expression is determined based on the virtual rotation inertia expression:

based on the expression of the virtual moment of inertia, the physical meaning of the equivalent inertia time constant is combined, and the equivalent inertia time constant expression can be determined as follows:

wherein, ω is_NThe rated angular speed of the doubly-fed fan is obtained.

In practical application, the determining the solving formula according to the three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the maximum power tracking model of the doubly-fed wind turbine, the generator transient model and the equivalent inertia time expression specifically includes:

according to the equivalent model of the doubly-fed wind turbine under the rotor speed time scale, the three-phase synchronous phase-locked loop dynamic equation and the relational expression, the DFIG electromagnetic torque increment transfer function relational expression is obtained as follows:

and (3) irrespective of the change of the mechanical torque, obtaining the incremental frequency domain expression of the rotor motion equation from the formula (7) as follows:

2H_dsΔω_r＝-ΔT_e (13)

from equation (12) and equation (13), in conjunction with the equivalent inertia time expression, the solution equation can be derived as follows.

Wherein H_eqRepresents the equivalent time constant of inertia, K_dvicDifferential gain representing virtual inertia control, s represents frequency domain differential operator, K_pvicProportional gain, T, representing virtual inertia control_fRepresenting the time constant of the filter, K_{p_pll}Indicating the proportional gain, K, of the phase-locked loop_{i_pll}Representing the integral gain, omega, of a phase-locked loop_r0Representing the initial rotor angular velocity, ω_s0Representing the initial synchronous angular velocity of the system, H_dRepresenting the inherent inertia time constant, K, of the doubly-fed wind turbine_psIndicating the proportional gain, K, of the speed controller_isIndicating the integral gain, omega, of the speed controller_NRepresenting the rated angular speed of the doubly-fed fan.

In this embodiment, the improved four-machine two-zone test system is processed as shown in fig. 6 by applying the above method, and the doubly-fed wind turbine replaces the synchronous machine of the node 1, and is connected to the node 5 in a unit connection manner of one transformer. The system frequency accident is simulated by a sudden load increase at the node 7, the test time is 5s, and the sudden load increase moment is taken as the starting time. FIG. 7 and FIG. 8 show the doubly-fed wind turbine under different working conditions (P)_e0.3 and P_e0.6) the result of comparing the estimated value of the equivalent inertia time constant with the true value.

As can be seen from fig. 7 and 8, the estimated values of the equivalent inertia time constant of the doubly-fed wind turbine under different working conditions are substantially consistent with the trend of the real value changing with time, and the accuracy of the method for estimating the equivalent inertia of the doubly-fed wind turbine based on the rotor kinetic energy virtual inertia control provided by the invention is verified.

The embodiment provides an equivalent inertia evaluation system of a doubly-fed wind turbine corresponding to the above method, as shown in fig. 9, the system includes:

the obtaining module a1 is configured to obtain steady-state information, where the steady-state information includes output power and grid frequency of the doubly-fed wind turbine.

And the initial rotor angular speed determining module A2 is used for calculating the initial rotor angular speed according to the output power of the doubly-fed wind turbine.

And the system initial synchronization angular speed determination module A3 is used for calculating the system initial synchronization angular speed according to the grid frequency.

And the equivalent inertia time constant determination module A4 is used for calculating an equivalent inertia time constant based on the system initial synchronous angular speed and the initial rotor angular speed, and the equivalent inertia time constant is used for evaluating the equivalent inertia of the doubly-fed wind turbine.

As an optional implementation manner, the equivalent inertia time constant determining module specifically includes:

the obtaining submodule is used for obtaining parameters of the doubly-fed wind turbine, and the parameters of the doubly-fed wind turbine comprise: the method comprises the following steps of gain parameters, frequency domain differential operators, time constants of a filter, inherent inertia time constants of the doubly-fed fan and rated angular speed of the doubly-fed fan.

And the equivalent inertia time constant determination submodule is used for calculating an equivalent inertia time constant according to the doubly-fed fan parameter, the system initial synchronous angular speed and the initial rotor angular speed.

As an optional implementation manner, the equivalent inertia time constant determination submodule specifically includes:

a solving unit for solving the formula

Calculating an equivalent inertia time constant, wherein H_eqRepresents the equivalent time constant of inertia, K_dvicDifferential gain, s-table representing virtual inertia controlDifferential operator in frequency domain, K_pvicProportional gain, T, representing virtual inertia control_fRepresenting the time constant of the filter, K_{p_pll}Indicating the proportional gain, K, of the phase-locked loop_{i_pll}Representing the integral gain, omega, of a phase-locked loop_r0Representing the initial rotor angular velocity, ω_s0Representing the initial synchronous angular velocity of the system, H_dRepresenting the inherent inertia time constant, K, of the doubly-fed wind turbine_psIndicating the proportional gain, K, of the speed controller_isIndicating the integral gain, omega, of the speed controller_NRepresenting the rated angular speed of the doubly-fed fan.

As an optional implementation manner, the doubly-fed wind turbine equivalent inertia evaluation system further includes:

and the relational expression determining module is used for determining a relational expression according to the rotating speed reference value and the active power output by the double-fed fan.

The first model building module is used for building a proportional differential virtual inertia control model based on the frequency of a phase-locked loop by taking the stator voltage phase angle increment as input and the electromagnetic torque reference value increment provided by the virtual inertia control as output.

And the second model building module is used for building a maximum power tracking model of the doubly-fed wind turbine by taking the electromagnetic power of the doubly-fed wind turbine as input and the reference value increment of the electromagnetic torque as output.

And the third model building module is used for building a generator transient model of the doubly-fed wind turbine by taking the electromagnetic torque reference value as input and the rotating speed of the rotor of the doubly-fed wind turbine as output.

And the equivalent inertia time constant expression determining module is used for determining an equivalent inertia time constant expression according to the first kinetic energy variation expression and the second kinetic energy variation expression. The first kinetic energy variation expression is a kinetic energy variation expression in the inertia response process of the double-fed fan before the additional virtual inertia control, and the second kinetic energy variation expression is a kinetic energy variation in the inertia response process of the double-fed fan after the additional virtual inertia control.

And the solving formula determining module is used for determining the solving formula according to a three-phase synchronous phase-locked loop dynamic equation, the relational expression, the proportional differential virtual inertia control model based on the phase-locked loop frequency, the generator transient model of the maximum power tracking model of the doubly-fed wind turbine and the equivalent inertia time expression.

As an optional implementation manner, the equivalent inertia time constant expression determining module specifically includes:

and the virtual moment of inertia expression determining submodule is used for determining a virtual moment of inertia expression according to the first kinetic energy variation expression and the second kinetic energy variation expression.

And the equivalent inertia time constant expression determining submodule is used for determining an equivalent inertia time constant expression based on the virtual rotation inertia expression.

The invention has the following technical effects:

(1) the method has the advantages of high calculation speed and low complexity, can accurately evaluate the equivalent inertia of the doubly-fed fan on line in real time only by measuring data of the doubly-fed fan in steady-state operation, and has good application value.

(2) The method has great significance in accurately evaluating the equivalent inertia of the doubly-fed wind turbine with the virtual inertia control by combining the measurement data of the system in steady-state operation, can provide scientific basis for the setting of the control parameters of the wind turbine generator and the distribution of the virtual inertia, is favorable for dispatching operators to master the space-time distribution condition of the system inertia, and further provides reference for the safety early warning and real-time emergency control strategy of the actual system.

(3) The existing method needs disturbance information, the method needs steady-state information, the existing method needs to accurately measure and calculate the frequency change rate according to a frequency curve, the calculation amount is large, the complexity is high, and the method does not need to calculate the frequency change rate. In addition, from the research purpose, most of the existing inertia evaluation methods focus on the equivalent inertia of the whole system, and the results of the method are still accurate after the two steps of improvement aiming at the inertia of the fan.

(4) The dynamic problem of the rotor speed control time scale is mainly a stability problem generated by the control of wind turbine related control, generator speed control, phase-locked loop control and the like and the dynamic state of the time scale energy storage element (rotor), and is suitable for virtual inertia response research. Therefore, the equivalent model of the doubly-fed wind turbine with the virtual inertia control under the rotor rotating speed time scale can solve the problem of evaluating the equivalent inertia of the doubly-fed wind turbine in a targeted manner.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.