CN112332441A

CN112332441A - Low-voltage ride through based double-fed fan full-wind-speed and initialization modeling

Info

Publication number: CN112332441A
Application number: CN202010840097.2A
Authority: CN
Inventors: 颜湘武; 孙颖; 李铁成
Original assignee: Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd; North China Electric Power University
Current assignee: Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd; North China Electric Power University
Priority date: 2020-08-18
Filing date: 2020-08-18
Publication date: 2021-02-05

Abstract

And (4) carrying out full wind speed and initialization modeling on the doubly-fed wind turbine based on low voltage ride through. The invention discloses a modeling method for full-wind-speed and quick-start initialization of a double-fed fan under low-voltage ride through experimental data, belonging to the technical field of new energy. With the increase of the wind power proportion, the influence on the stability of the power grid is increasingly prominent, and the method has important significance on accurate modeling of the power grid. According to the method, the modeling research of the wind power plant is carried out according to the low voltage ride through test data provided by a certain power science research institute, wherein the modeling research comprises the operation conditions of different wind speeds, different voltage drop degrees and the like. A quick start model of the doubly-fed wind turbine generator set under full-wind-speed operation is established, operation of the wind turbine generator set and a low-voltage ride-through protection device are judged according to actually-measured data and curve analysis, and a control mode is determined; and (3) combining the operation data, giving the initialized parameters of a part of fans, so that the system model can be quickly started and stably operated within 1 second. The method provided by the invention can accurately model the actual wind power plant and has higher actual application value for the related test of the wind power plant.

Description

Low-voltage ride through based double-fed fan full-wind-speed and initialization modeling

Technical Field

The invention belongs to the technical field of new energy, and particularly relates to a low-voltage ride through based full-wind speed and initialization modeling method suitable for a double-fed wind turbine generator.

Background

Due to the increasingly serious environmental and resource problems, the low cost of wind energy utilization, mature technology and the like, wind power generation becomes a new energy power generation technology which is relatively fast in growth in a power system, and the development of wind power becomes an extremely important measure for improving the economic operation of the power system. The single machine capacity and the wind power plant construction scale of the wind generating set are gradually enlarged, but the randomness and the intermittence of wind power can generate certain influence on the stable operation of a power system, the low voltage ride through problem of the wind power plant when a power grid fails is highly concerned along with the continuous development of the wind power generation system, and all the wind power plants which are connected in a grid at present are required to have low voltage ride through capability, so that for the power system comprising the wind power plant, a correct mathematical model needs to be established and the system needs to be subjected to simulation analysis.

If the existing part of wind power generation fields are subjected to performance tests or used for development and research of new technologies, a large amount of manpower and material resources are needed, and immature technologies may damage equipment to influence the service life and the operation safety of the equipment. Therefore, the existing entity wind power plant is subjected to targeted modeling and used for detection and development, and the method is very significant.

Disclosure of Invention

The invention provides a strategy method for carrying out low-voltage ride through based double-fed fan full-wind-speed modeling and quick starting according to field measured data. According to the national standard GB/T19963 plus 2011 technical stipulations for connecting a wind power plant to a power system, the inner Mongolia power science research institute performs a low-voltage ride-through function field test on a 35kV wind power generation unit of a certain wind power plant. The North China Power university carries out wind power plant modeling research according to the low voltage ride through function test data of the doubly-fed wind turbine generator, which is provided by the inner Mongolia institute of Electrical science.

The specific modeling process is described below. (1) According to the researched double-fed wind generating set, a single double-fed wind generating set grid-connected simulation model with the rated power of 1.5MW is built based on MATLAB, and is shown in figure 1. (2) On the basis of the doubly-fed wind power model, reasonable model parameters are determined so as to meet the requirements of practical application. For the simulation application of the power system, the electrical behavior of the wind turbine generator after the power grid fails is relatively concerned, and the main parameters influencing the electrical characteristics of the wind turbine generator can be identified, mainly the parameters influencing the active and reactive characteristics. Identification of parameters of doubly-fed wind turbine generator set is carried out on the basis of low-voltage ride-through data of existing doubly-fed wind turbine generator setThe data include various operating conditions such as different wind speeds and different voltage drop degrees, and the electrical characteristics of the double-fed wind turbine generator are comprehensively reflected. As can be seen from fig. 2, the generator has little influence on the active and reactive outputs by using different parameters. (3) And determining a main fan control mode, wherein the fan is fully started under the condition of normal operation of the fan, the reactive power is zero, and the unit power factor operation can be realized. (4) Determining a main low-voltage ride-through protection device, connecting a Crowbar circuit and a machine side frequency converter in parallel, and after action, equivalently, adopting a resistor for short circuit of a rotor loop. (5) Constructing a full-wind-speed operation model of the doubly-fed wind generating set, comprising

It can be known that the mechanical power output by the wind turbine, the wind speed and the power coefficient C_pIt is related. In the full wind speed range, the running state of the wind turbine generator is divided into three stages, namely a constant power coefficient variable rotating speed stage, a constant rotating speed variable power coefficient stage and a variable pitch constant power stage. During the three phases of operation, the parameters of the wind turbine are changed as shown in fig. 3, 4 and 5. And when the wind speed is less than the cut-in wind speed or greater than the cut-out wind speed, the wind turbine generator is not operated. The actual operating point condition of the fan can be determined according to the active power output by the double-fed fan and the change of the pitch angle. (6) The existing model is initialized, so that the model can be quickly stabilized after being started. Giving an initial slip ratio s, an electrical angle th, three-phase stator currents ias, ibs and ics and phase angles phasa, phasbs and phascs of stator currents to the fan, and comparing the initialized quick start result with the result shown in fig. 6.

Drawings

Fig. 1a and 1b are grid-connected simulation model diagrams of the doubly-fed wind generating set.

Fig. 2 is a graph comparing different generator parameters.

FIG. 3 is a graph of output power versus wind speed.

FIG. 4 is a graph of rotational speed versus wind speed.

FIG. 5 is a graph of pitch angle versus wind speed.

Fig. 6 is a comparison before and after initialization.

Detailed Description

The invention is described in further detail below with reference to the accompanying drawings. The attached figures 1a and 1b are grid-connected simulation model diagrams of a doubly-fed wind generating set, and the 1.5MW doubly-fed wind generating set is composed of a fan prime mover, a generator, a rotor side converter and a grid side converter. One end of the grid-side converter is connected with a stator of the double-fed wind driven generator, the other end of the grid-side converter is connected with the machine-side converter through a direct current bus, the machine-side converter is connected with a rotor of the double-fed wind driven generator, and the Crowbar device is located between the machine-side converter and the double-fed wind driven generator set, so that hardware protection of low-voltage crossing of a fan is achieved. The part of the double-fed wind power generation system merged into the power grid mainly comprises a low-voltage and medium-voltage step-up transformer, a low-voltage generation device, line impedance, a medium-voltage and high-voltage step-up transformer and a large power grid.

Fig. 2 is a comparison graph of different generator parameters, and the generator has little influence on active and reactive outputs by adopting different parameters. The output characteristic of the wind turbine generator is mainly determined by a control system, the wind turbine generator is small in capacity and high in response speed, and even if the parameters of the wind turbine generator with the same capacity are different to a certain extent, the response speed difference is not obvious, so that the influence on the overall output characteristic is small. From the above analysis on the influence of the physical parameters of the wind power, it can be seen that different parameters have certain influence on the local fluctuation of the external characteristics of the power output of the wind turbine generator, and have little influence on the overall curve form.

Crowbar usually adopts rotor current as a control signal, and after action, the structure of an asynchronous generator is changed, so that the control of a frequency converter is disabled, and reactive power with certain capacity needs to be absorbed from a system, thereby generating great influence on the reactive output of the generator. The Crowbar circuit is connected with the machine side frequency converter in parallel, and after the Crowbar circuit acts, the rotor loop is equivalently short-circuited by adopting a resistor. Crowbar usually adopts rotor current as a control signal, and after action, the structure of an asynchronous generator is changed, so that the control of a frequency converter is disabled, and reactive power with certain capacity needs to be absorbed from a system, thereby generating great influence on the reactive output of the generator.

The power captured by a wind turbine from the wind may be expressed as

In the formula: lambda is the tip speed ratio, beta is the pitch angle, R is the wind turbine blade radius, rho is the air density, v is the wind speed, A is the swept area of the blade, lambda is_lFor intermediate variables in formulaic simplification, C_p(beta lambda) is the wind energy conversion efficiency coefficient, omega, of a wind turbine_rIs the generator rotor speed. As can be seen from the formula (1), the mechanical power output by the wind turbine, the wind speed and the power coefficient C_pIt is related.

Constructing a full wind speed operation model of the doubly-fed wind generating set, wherein the operation state of the wind generating set is divided into three stages within a full wind speed range: the method comprises a constant power coefficient variable rotating speed stage, a constant rotating speed variable power coefficient stage and a variable pitch constant power stage. During the three phases of operation, the parameters of the wind turbine are changed as shown in fig. 3, 4 and 5.

The constant power coefficient variable speed stage: when the wind speed is higher than the cut-in wind speed, the maximum value C is taken for realizing the maximum wind energy capture wind power coefficient_{p max}0.48, as shown in fig. 1, when β is 0, λ_opt8.1. For realizing maximum power point tracking control, wind turbine rotation speed omega_mWill increase with increasing wind speed up to the rated speed of the wind turbine.

Stage of constant rotating speed and variable power coefficient: when the wind speed increases but does not exceed the rated wind speed, the rotating speed is kept at the rated value and is not increased any more, and the maximum power point in the stage is the output power of the wind turbine when the rotating speed is the rated value. Meanwhile, the speed ratio of the blade tip and the power coefficient are reduced along with the increase of the wind speed, the pitch angle is unchanged, and the output power of the wind turbine is continuously increased until the rated power is reached.

A variable pitch constant power stage: when the wind speed exceeds the rated wind speed (12.5m/s) and is less than the cut-out wind speed, in order to ensure the stable operation of the wind turbine, the pitch angle is increased along with the increase of the wind speed so as to keep the output power close to the rated value, and the maximum power in the phase is the rotating speed which is the rated value (omega)_m1.2), the output power of the wind turbine, i.e. the rated power.

And when the wind speed is less than the cut-in wind speed or greater than the cut-out wind speed, the wind turbine generator is not operated. Therefore, the actual operating point condition of the fan can be determined according to the active power output by the double-fed fan and the change of the pitch angle.

On the basis of the above work, in order to make the model quickly reach stability after starting, the initialization work is performed on the existing model. The scheme is that an initial slip rate s, an initial electrical angle th, stator three-phase currents ias, ibs and ics and phase angles phasa, phasbs and phascs of stator currents are given to the fan. The initial data is obtained by reversely deducing the data after the stable operation of the fan, so that a large amount of data are recorded and processed in the earlier stage when the fan is stable. Giving the slip rate during starting according to the rotating speed during stabilization; and according to the three-phase current of the stator when the stator is stable, providing corresponding data of the three-phase current when the stator is started. Electrical angle th is p × mechanical angle, where p is the pole pair number and mechanical angle is 360 °, i.e. 2 pi.

The wind speed received by the wind driven generator and the corresponding rotating speed have the following relationship:

the rotational speed and the wind speed basically present a linear relationship. According to the statistical wind speed and the corresponding rotational speed data, the basic relation omega of the rotational speed and the wind speed is obtained through the fitting of data linear regression_pu0.0997 v-0.0278. When the per unit value of the rotating speed exceeds the rated rotating speed of 1.2, the per unit value is limited to be the rated rotating speed of 1.2. Different slip, wind turbineWith different initial speeds, the relation being Tis 0.9672 omega_pu+0.0202。

Taking a high wind (heavy load) as an example, when the wind speed is 14m/s, the rotating speed at the moment exceeds the rated rotating speed according to the fitting relation, so that the rotating speed is 1.2, the slip ratio is-0.2, the initial rotating speed of the corresponding wind turbine is 1.18, and the parameters are taken as initialization data for simulation. The initialization results are shown in fig. 6, and the system reaches a steady state within 1 second after the system is started after the initialization, which is faster than before the initialization.

Claims

1. a doubling-fed wind turbine modeling and initialization method based on LVRT, is characterized in that, the identification of DFIG parameters is carried out on the basis of existing LVRT data of DFIG, and these data include different wind speeds. , different voltage drop degrees and other operating conditions, which more comprehensively reflect the electrical characteristics of the doubly-fed wind turbine. The active and reactive output curves of the doubly-fed wind turbine show that the reactive power is proportional to the degree of voltage sag. It is inferred that the reactive power is controlled by the voltage sag during the low voltage ride through; after the low voltage ride through, the reactive power value returns to Zero, indicating that the normal reactive power control state is carried out, the fan realizes unit power factor operation, and the active power realizes the maximum power tracking control during the normal operation process, and the Crowbar device is activated during the low wear process to consume excess output active power.

2. A low-voltage ride through-based DFIG modeling and initialization method, characterized in that a full wind speed operation model of the DFIG is constructed. The change rule of fan parameters with different operating states in the full wind speed range is clarified. When the wind speed is lower than the cut-in wind speed or greater than the cut-out wind speed, the wind turbine will not run. The actual operating point of the fan is determined according to the output active power of the double-fed fan and the change of the pitch angle.

3. A low-voltage ride-through-based modeling and initialization method for a doubly-fed wind turbine, characterized in that, according to data under different working conditions, the relationship between some start-up parameters of the wind turbine and wind speed is clarified. According to the wind speed, the initial slip s, electrical angle th, stator three-phase current ias, ibs, ics and stator current phase angle phasas, phasbs, phascs are automatically given to the fan, so that the model can quickly reach stability within 1s after startup .