阅读说明：本技术 垂直轴风力机试验用磁粉制动器的磁滞特性测试方法 (Magnetic powder brake hysteresis characteristic testing method for vertical axis wind turbine test ) 是由 吴延峰 田凯 马明慧 徐贤申 杨宗霄 宋磊 于 2021-07-20 设计创作，主要内容包括：垂直轴风力机试验用磁粉制动器的磁滞特性测试方法,将磁粉制动器与垂直轴风力机中垂直轴风轮的垂直轴通过联轴器相连接,然后通过风源向垂直轴风轮吹风,进行测试,对每个转速下不同电流下输出扭矩进行多次测量通过筛选获得最为准确的一组进行曲线拟合得到垂直轴风力机试验用磁粉制动器的静态磁滞特性曲线。检测精度高,能够为垂直轴风轮精密加载提供有效的依据,为后续垂直风轮加载控制方法提供准确的依据,大大提高了垂直轴风力机风轮的性能测试精度。(The magnetic powder brake is connected with a vertical shaft of a vertical shaft wind wheel in the vertical shaft wind turbine through a coupler, then the vertical shaft wind wheel is blown by a wind source for testing, output torque under different currents at each rotating speed is measured for multiple times, and the most accurate group of the output torque is obtained through screening and curve fitting to obtain a static hysteresis characteristic curve of the magnetic powder brake for the vertical shaft wind turbine test. The detection precision is high, effective basis can be provided for the precise loading of the vertical axis wind wheel, accurate basis is provided for the subsequent vertical wind wheel loading control method, and the performance test precision of the vertical axis wind turbine wind wheel is greatly improved.)

1. The magnetic powder brake hysteresis characteristic test method for the vertical axis wind turbine test is characterized in that the magnetic powder brake is connected with a vertical axis of a vertical axis wind wheel in a vertical axis wind turbine, and then wind is blown to the vertical axis wind wheel through a wind source for testing, and the method specifically comprises the following steps:

1) starting a wind source and collecting wind speed;

2) adjusting the wind speed to enable the rotating speed of the wind wheel to reach a preset value, recording the stable wind speed, and recording the rotating speed of the wind wheel;

3) the size of controlling magnetic powder brake input current through the current controller, and recording the output torque value of the magnetic powder brake: the size of the input current of the magnetic powder brake is linearly adjusted through a current controller, and the method specifically comprises the following steps: the input current value of the magnetic powder brake is increased from zero to a zero value after the vertical axis wind wheel stops rotating; recording each input current value data and the output torque value data of the corresponding magnetic powder brake;

4) repeating the step 3) for multiple times, namely, carrying out equal-current multi-period measurement to obtain output torque value data of each input current value in different periods;

5) screening the output torque value of each input current value obtained in the step 4) in different periods: the method specifically comprises the following steps:

firstly, apply the formula

Calculating the residual error of each period of data; in equation (1): t is_iThe output torque measured in the ith cycle under the same current, i is 1,2,3, …, n, n is the total cycle number;the arithmetic mean value of the output torque in the period actually measured under the same current is obtained; v_iIs T_iThe residual error of (2);

then, applying the formula

Calculating the proportion of each residual error to the arithmetic mean value of the output torque in the corresponding period, and eliminating the output torque with overlarge fluctuation, namely obtaining the output torque value with k larger than 8 percent, thereby realizing data screening;

6) performing third, fourth and fifth order curve fitting on each period data screened in the step 5) according to the input current increasing section and the input current decreasing section by using the formula (3) as a fitting index,

J＝∑(X_i-T_i)² (3)

wherein J represents the curve fitting accuracy, X_iFitting value, T, representing output torque_iA test value representing output torque;

through the step, the periodic data with the minimum J value, namely the most accurate group of data, is selected from the plurality of periodic data;

7) adjusting the wind speed to enable the rotating speed of the wind wheel to reach another preset value, recording the stable wind speed, and recording the rotating speed of the corresponding wind wheel;

8) repeating the steps 3) to 7) for N-1 times, wherein N is the number of the selected wind wheel rotating speeds;

9) and drawing a curve graph in a rectangular coordinate system according to the recorded data:

specifically, under each wind wheel rotating speed, output torques corresponding to different current values are drawn in a rectangular coordinate system to obtain a relation curve between the current and the torque of the magnetic powder brake.

2. The magnetic powder brake hysteresis characteristic testing method for the vertical axis wind turbine test according to claim 1, characterized in that: wind speed is collected by an anemoscope, the rotating speed of a wind wheel is collected by a rotating speed sensor, output torque is collected by a torque coupler, and the anemoscope, the rotating speed sensor and the torque coupler are all in communication connection with a monitoring computer.

3. The magnetic powder brake hysteresis characteristic testing method for the vertical axis wind turbine test according to claim 1, characterized in that: wherein, the recording and the screening of the data are processed by a monitoring computer.

4. The magnetic powder brake hysteresis characteristic testing method for the vertical axis wind turbine test according to claim 1, characterized in that: the current controller works under the control of the monitoring computer, and the current of the magnetic powder brake coil is controlled by the current controller.

5. The test system for the hysteresis characteristic test method of the magnetic powder brake for the vertical axis wind turbine test according to any one of claims 1 to 4, wherein: the method comprises the following steps:

the wind power device is used for providing a wind source, the wind power device blows wind to the vertical axis wind wheel, and an anemoscope used for detecting wind speed is arranged between the wind power device and the vertical axis wind wheel;

the wind speed sensor is connected with a vertical shaft in the vertical shaft wind wheel, the rotating speed sensor is used for detecting the rotating speed of the vertical shaft wind wheel, and the torque coupler is used for detecting the torque output by the magnetic powder brake.

6. The test system of claim 5, wherein: and the current controller is used for controlling the current of the magnetic powder brake coil, and a control signal output by the monitoring computer is input to the magnetic powder brake through the current controller.

7. The test system of claim 5, wherein: the vertical shaft of the vertical shaft wind wheel is directly inserted into the mounting hole of the outer rotor of the magnetic powder brake or fixedly connected with the protruding shaft of the magnetic powder brake by adopting a coupler.

Technical Field

The invention relates to the technical field of magnetic powder brake testing, in particular to a magnetic hysteresis characteristic testing method of a magnetic powder brake for a vertical axis wind turbine test.

Background

Wind power is increasingly gaining importance as an important component of the world energy structure. At the beginning of the development of wind power, the wind power generation is mainly focused on horizontal axis wind power generation, and through the rapid development of recent years, the development of the wind power tends to be saturated, and a vertical axis wind turbine for low wind speed wind power generation gradually becomes a current research hotspot.

After the vertical axis wind turbine is manufactured, a test is usually required to test the performance of the vertical axis wind turbine, the vertical axis wind turbine is one of the key components of the vertical axis wind power generation system, and the design or selection of the parameters directly affects the working performance of the vertical axis wind power generation system, so that the simulation loading test verification needs to be performed on the vertical axis wind turbine to make up for the deficiency of theoretical analysis (that is, the magnetic powder brake for the test of the vertical axis wind turbine is actually the magnetic powder brake for the performance test of the vertical axis wind turbine).

In the vertical axis wind wheel simulation loading experiment, a magnetic powder brake is adopted to provide loading torque so as to simulate the moment between magnetic poles of a generator. The brake is realized by using magnetic material as working medium and controlling torque by adjusting exciting current. The rotor of the magnetic powder brake is connected with the wind wheel, and the stator is fixed on the frame. Meanwhile, if the performance detection system is in accident, and the torque is overloaded, the magnetic powder brake can automatically slip to play an overload protection role.

The magnetic powder brake has the advantages of simple structure, low noise, convenient control, weak mechanical vibration and the like, and is mainly applied to occasions such as a tension control system, a torque power test platform, low-power precise loading and the like. With the development of science and technology, the application of the magnetic powder brake in the precise loading occasion is more and more extensive.

The magnetic powder brake mainly comprises a driving rotor, a driven rotor and an exciting coil. A large amount of magnetic powder exists between a driving rotor and a driven rotor of the magnetic powder brake, the magnetic powder is metal particles which are small in size and subjected to strong magnetization, the metal particles are good in wear resistance, and torque is transmitted by utilizing interaction between the metal particles;

the working principle of the magnetic powder brake is as follows:

when the coil is not electrified, the driving rotor rotates, magnetic powder is thrown on the inner wall of the driving rotor under the action of centrifugal force, the magnetic powder is not in contact with the driven rotor, and the driving rotor idles;

when the coil is connected with a power supply, an electromagnetic field is generated, the working medium magnetic powder is magnetized under the action of magnetic lines of force to form a magnetic powder chain and is polymerized between the fixed magnetizer and the rotor, so that the aim of outputting braking torque (output torque for short) to brake is fulfilled;

the relation between the input control current and the output torque of the magnetic powder brake can be obtained by utilizing the Moire Coulomb principle:

wherein, T is torque, N is coil number, D_mOuter diameter of brake, mu₀Is the air gap permeability, mu_δMagnetic permeability of magnetic powder, I coil current intensity, mu_iIs the permeability of the iron core, S_δIs the cross-sectional area of the magnetic powder in the gap S_iIs the cross-sectional area of the core, /)_δIs the middle width of the magnetic circuit, /)_iIs the core length in the magnetic circuit, L_mThe width of the magnetic powder brake coil;

from the above formula, other physical quantities than the coil current strength I can be considered to be constant. However, in the case of a magnetic material, the magnetic permeability is not constant, and depends on the magnetic field intensity and frequency. When the ferrite is subjected to an external magnetic field H, for example, when a current flows through a coil wound on a ferrite bead, it becomes magnetized. An increase in magnetic field strength in turn causes an increase in magnetic flux density, which, when increased to a certain extent, tends to stabilize, known as field saturation. The saturation field H of the soft magnetic material is only a few tenths to a few oersteds. As saturation approaches, the permeability rapidly decreases and approaches the permeability of air (relative permeability of 1). Because of hysteresis of magnetic resistance, saturation of magnetic flux, and non-constancy of magnetic permeability, the input current and the output torque do not exhibit an approximately linear relationship, and when the input current increases linearly and decreases linearly, the actual torque loading characteristic is not a linear function. When the input current is gradually increased, the output torque of the magnetic powder brake rises along the rising section, and when the input current is gradually decreased, the output torque of the magnetic powder brake does not fall along the original path, but is obviously higher than the rising section when the current falls to the same value when rising, and the typical hysteresis phenomenon is presented.

The magnetic powder brake's hysteresis lag characteristic makes its loading quality and rapidity all reduce to some extent, has influenced the accuracy of vertical axis wind wheel simulation loading experiment, consequently before using magnetic powder brake in the vertical axis wind wheel simulation loading experiment, need measure magnetic powder brake hysteresis lag characteristic usually to obtain magnetic powder brake's loading characteristic, thereby better application and control magnetic powder brake, and then improve the effect of vertical axis wind wheel simulation loading experiment.

At present, the magnetic powder brake hysteresis characteristic measuring method is single, and magnetic core material hysteresis loops are mostly directly measured, so that the magnetic powder brake hysteresis characteristic is obtained. Obviously, the method does not accord with a real loading working condition, the actual load condition of the wind wheel is not considered, the influence of the size of the input excitation current on the magnetic hysteresis characteristic is not considered, if the corresponding control adjustment scheme is given according to the related magnetic hysteresis characteristic obtained by the method, the purpose of precise loading is further achieved, and a certain degree of error is inevitably generated in the process, so that a more reasonable magnetic powder brake magnetic hysteresis characteristic testing method is needed to be provided.

Disclosure of Invention

The invention aims to provide a hysteresis characteristic testing method of a magnetic powder brake for a vertical axis wind turbine test.

In order to achieve the purpose, the invention adopts the technical scheme that: the magnetic powder brake is connected with a vertical shaft of a vertical shaft wind wheel in a vertical shaft wind turbine, and then the vertical shaft wind wheel is blown by a wind source for testing, wherein the magnetic powder brake is specifically as follows:

1) starting a wind source and collecting wind speed;

2) adjusting the wind speed to enable the rotating speed of the wind wheel to reach a preset value, recording the stable wind speed, and recording the rotating speed of the wind wheel;

3) the size of controlling magnetic powder brake input current through the current controller, and recording the output torque value of the magnetic powder brake:

specifically, the magnitude of magnetic powder brake input current is adjusted through the linearity of current controller, specifically: the input current value of the magnetic powder brake is increased from zero to a zero value after the vertical axis wind wheel stops rotating; recording each input current value data and the output torque value data of the corresponding magnetic powder brake;

4) repeating the step 3) for multiple times, namely, carrying out equal-current multi-period measurement to obtain output torque value data of each input current value in different periods;

5) screening the output torque value of each input current value obtained in the step 4) in different periods: the method specifically comprises the following steps:

firstly, apply the formula

Calculating the residual error of each period of data; in equation (1): t is_iThe output torque measured in the ith cycle under the same current, i is 1,2,3, …, n, n is the total cycle number;the arithmetic mean value of the output torque in the period actually measured under the same current is obtained; v_iIs T_iThe residual error of (2);

then, applying the formula

Calculating the proportion of each residual error to the arithmetic mean value of the output torque in the corresponding period, and eliminating the output torque with overlarge fluctuation, namely obtaining the output torque value with k larger than 8 percent, thereby realizing data screening;

6) performing third, fourth and fifth order curve fitting on each period data screened in the step 5) according to the input current increasing section and the input current decreasing section by using the formula (3) as a fitting index,

J＝∑(X_i-T_i)² (3)

wherein J represents the curve fitting accuracy, X_iFitting value, T, representing output torque_iA test value representing output torque;

through the step, the periodic data with the minimum J value, namely the most accurate group of data, is selected from the plurality of periodic data;

7) adjusting the wind speed to enable the rotating speed of the wind wheel to reach another preset value, recording the stable wind speed, and recording the rotating speed of the corresponding wind wheel;

8) repeating the steps 3) to 7) for N-1 times, wherein N is the number of the selected wind wheel rotating speeds;

9) and drawing a curve graph in a rectangular coordinate system according to the recorded data:

specifically, under each wind wheel rotating speed, output torques corresponding to different current values are drawn in a rectangular coordinate system to obtain a relation curve between the current and the torque of the magnetic powder brake.

In the test method, the wind speed is collected by an anemoscope, the rotating speed of the wind wheel is collected by a rotating speed sensor, the output torque is collected by a torque coupler, and the anemoscope, the rotating speed sensor and the torque coupler are all in communication connection with a monitoring computer.

In the test method, the recording and screening of the data are processed by a monitoring computer.

In the testing method, the current controller works under the control of the monitoring computer, and the current of the magnetic powder brake coil is controlled by the current controller.

This scheme still relates to a test system, includes:

the wind power device is used for providing a wind source, blows air to the vertical axis wind wheel, and an anemoscope used for detecting wind speed is arranged between the wind source and the vertical axis wind wheel;

the wind speed sensor is connected with a vertical shaft in the vertical shaft wind wheel, the rotating speed sensor is used for detecting the rotating speed of the vertical shaft wind wheel, and the torque coupler is used for detecting the torque output by the magnetic powder brake.

The test system is also provided with a current controller for controlling the current of the magnetic powder brake coil, and a control signal output by the monitoring computer is input to the magnetic powder brake through the current controller.

In the test system, a vertical shaft of a vertical shaft wind wheel is directly inserted into a mounting hole of an outer rotor of the magnetic powder brake or fixedly connected with a protruding shaft of the magnetic powder brake by adopting a coupler.

Has the advantages that:

according to the working condition of the vertical axis wind wheel test, the magnetic hysteresis characteristic of the magnetic powder brake is indirectly tested, the one-sidedness of the measurement in the prior art is overcome, the measurement signal is recorded through data processing software, the relation between the dynamic parameters (the rotor speed n, the input current I and the output torque T) of the magnetic powder brake can be obtained after the measurement signal is processed, the measured data is high in precision, and the magnetic hysteresis characteristic of the magnetic powder brake can be truly reflected.

The method adopts an equal current single-value multi-period mode on the basis of an equal current single-value single-period acquisition mode, namely, multiple single-value single-period tests are carried out at the rotating speed of the same magnetic powder brake, so that the error of single-value single-period data acquisition is avoided. In addition, the method screens the acquired data, selects the data in one period with more accurate data in multiple periods, reduces random errors of initial data, improves the precision of test results, and effectively avoids systematic errors caused by direct measurement.

According to the method, experimental data are divided into an ascending section and a descending section, and two curves are obtained by separately fitting discrete data, so that not only is precision control improved, but also a reliable basis is provided for the magnetic powder brake to be applied to precision loading in a universal test bed device for performance detection of the vertical axis wind wheel, and the performance test precision of the vertical axis wind turbine wind wheel is greatly improved; the method has the advantages of good universality, strong replaceability and low cost, and can be applied to hysteresis characteristic tests of magnetic powder brakes of various models.

Drawings

FIG. 1 is a structural diagram of a magnetic powder brake hysteresis characteristic testing system of a vertical axis wind turbine according to the invention;

FIG. 2 is a schematic flow chart of the method for testing magnetic particle brake hysteresis characteristics of the vertical axis wind turbine according to the invention;

FIG. 3 is a graph of magnetic particle brake current versus torque measured in accordance with an embodiment of the present invention;

FIG. 4 is a graph of control current versus output torque measured at a vertical axis rotor speed of 200rpm with a slow increase in input current from 0A;

FIG. 5 is a graph of control current versus output torque measured at a vertical axis rotor speed of 200rpm with decreasing input current;

FIG. 6 is a graph of control current versus output torque measured at a vertical axis wind turbine speed of 600rpm with a slow increase in input current from 0A;

fig. 7 is a graph of control current versus output torque measured at a vertical axis rotor speed of 600rpm with decreasing input current.

Detailed Description

The invention will be described in further detail below with reference to the accompanying figures 1-7 and examples.

The magnetic powder brake to be tested (hereinafter referred to as the magnetic powder brake) is connected with a vertical shaft of a vertical shaft wind wheel in the vertical shaft wind turbine, and then the vertical shaft wind wheel is blown by a wind source to carry out testing.

As shown in FIG. 1, the testing system used in the present invention comprises a wind power device for providing a wind source, a vertical axis wind wheel connected with a magnetic particle brake, an anemometer for testing the wind speed of the wind source, a rotational speed sensor for testing the rotational speed of the vertical axis wind wheel, a torque coupler for testing the output torque of the magnetic particle brake, the magnetic powder brake system comprises a current controller for controlling the current of a coil of the magnetic powder brake (input current of the magnetic powder brake for short), an A/D converter for converting a rotating speed signal (which refers to the rotating speed of a vertical axis wind wheel detected by a rotating speed sensor), a torque signal (which refers to the torque signal output by the magnetic powder brake detected by a torque coupler) and a wind speed signal (which refers to a wind speed signal coming from a wind source detected by a wind speed meter), and a monitoring computer for monitoring the operation of the whole system, wherein the monitoring computer is provided with signal analysis software.

The wind source is a simulated natural wind source of the test system, can be provided by a wind power device, and can control the size of the incoming wind speed (can realize the change of the wind speed of 0-25 m/s) by adjusting the power frequency of the wind power device through a variable frequency speed regulator.

The anemoscope is placed in the wind flow forward direction of a wind source, collects wind speed v, is connected with the A/D converter at the output end, transmits a wind speed signal to the monitoring computer, and sends an instruction signal to the current controller after being judged by the monitoring computer; the current controller outputs a current signal, and the magnetic powder brake receives the current signal and enters a working state. In this embodiment, the anemoscope is composed of a fixed support and a wind measurement probe.

The current controller controls the input current of the magnetic powder brake by receiving the instruction signal sent by the monitoring computer.

The magnetic powder brake is connected with the vertical shaft wind wheel, and according to the structure of the magnetic powder brake, the vertical shaft of the vertical shaft wind wheel can be directly inserted into a mounting hole of an outer rotor of the magnetic powder brake; or the coupler is fixedly connected with the protruding shaft of the magnetic powder brake.

The signal analysis software in the monitoring computer is provided with a data acquisition module, a data screening module and a data storage module, the data processing efficiency is improved through real-time data acquisition, the acquired output torque value of the magnetic powder brake is ensured to correspond to the current input current of the magnetic powder brake, errors caused by data interaction delay are avoided, the data screening performs error processing on the acquired original data to reduce the influence of random errors, and the data after screening is stored in a database so as to be analyzed and applied at a later stage. The data mentioned in this paragraph are mainly the output torque of the magnetic powder brake, the rotor speed in the magnetic powder brake (also the vertical axis wind wheel speed, referred to as wind wheel speed for short) and the input current of the magnetic powder brake.

As shown in fig. 2, the hysteresis characteristic testing process of the magnetic powder brake for the vertical axis wind turbine test is as follows:

initializing the monitoring computer parameters and then

1) And starting a wind source, and collecting wind speed, wherein the starting wind speed is generally 5 m/s.

2) And adjusting the wind speed to enable the rotating speed of the wind wheel to reach a first stable preset value, then recording the stable wind speed, and recording the corresponding rotating speed of the wind wheel, wherein the vertical shaft of the vertical shaft wind wheel simultaneously drives the outer rotor of the magnetic powder brake to rotate.

In the step, the rotating speed of the wind wheel needs to be observed in the process of adjusting the wind speed, if the rotating speed of the wind wheel is unstable, the speed is regulated through a frequency converter, and the wind speed is continuously collected to judge until the wind speed is stable.

3) The size of controlling magnetic powder brake input current through the current controller, and recording the output torque value of the magnetic powder brake:

the size of the input current of the magnetic powder brake is linearly adjusted through a current controller, and the method specifically comprises the following steps: the electric input current value of the magnetic powder brake is increased from zero to a value of zero after the vertical axis wind wheel stops rotating; recording each input current value data and the output torque value data of the corresponding magnetic powder brake;

4) repeating the step 3) for multiple times, namely, carrying out equal-current multi-period measurement to obtain output torque value data of each input current value in different periods;

in this embodiment, the total number of times of step 3) is performed is 6 times at the same rotor speed. I.e. 6 cycles of measurement at iso-current.

5) Screening the output torque value of each input current value obtained in the step 4) in different periods:

the method specifically comprises the following steps:

firstly, apply the formula

Calculating the residual error of each period of data; in equation (1): t is_iThe output torque measured in the ith cycle under the same current, i is 1,2,3, …, n, n is the total cycle number;the arithmetic mean value of the output torque in the period actually measured under the same current is obtained; v_iIs T_iThe residual error of (2);

then, applying the formula

Calculating the proportion of each residual error to the arithmetic mean value of the output torque in the corresponding period, and eliminating the output torque with overlarge fluctuation, namely obtaining the output torque value with k larger than 8 percent, thereby realizing data screening;

6) performing least square curve fitting on each period data screened in the step 5) according to the input current increasing section and the input current decreasing section, performing third-order, fourth-order and fifth-order curve fitting by using a formula (3) as a fitting index,

J＝∑(X_i-T_i)² (3)

wherein J represents the curve fitting accuracy, X_iFitting value, T, representing output torque_iA test value representing output torque;

through the step, the periodic data with the minimum J value, namely the most accurate group of data, is selected from the plurality of periodic data;

description of the drawings:

7) repeating the step 2), adjusting the wind speed to enable the rotating speed of the wind wheel to reach the next preset value, recording the stable wind speed, and recording the rotating speed of the corresponding wind wheel;

8) repeating the steps 3) to 6) for N-1 times, wherein N is the number of the selected wind wheel rotating speeds;

in this example, N is 2. I.e. step 2) was performed a total of 2 times.

In the embodiment, when the step 2) is carried out for the first time, the preset value of the rotating speed of the wind wheel is 200 r/min;

in the embodiment, when the step 2) is performed for the second time, the predetermined value of the rotation speed of the wind wheel is 600 r/min.

9) Drawing a curve chart in a rectangular coordinate system according to the screened most accurate data:

specifically, the relationship curve of the current and the torque of the magnetic powder brake is drawn in a rectangular coordinate system according to the output torque corresponding to different current values at each wind wheel rotating speed, as shown in fig. 3. When the input current is 0A, a certain output torque is also provided, so that the phenomenon of delaying the rotation under the condition of load can be avoided.

The characteristic analysis is performed according to fig. 3, specifically:

1) when the input current increases progressively, the output torque of the magnetic powder brake rises along the rising section; when the input current is decreased progressively, the output torque of the magnetic powder brake is decreased along the descending section, but is obviously higher than the ascending section, and the typical hysteresis phenomenon is presented;

2) the curves of the magnetic powder brake at the rotating speed of 200r/min and 600r/min are inconsistent, and the output torque of the magnetic powder brake is influenced by the rotating speed.

3) The curve of the output torque changing with the input current, whether in the rising section or the falling section, is larger as the rotating speed increases.

The method divides the experimental data into an ascending section and a descending section, and can meet the requirement of experimental equipment on precision control;

under the condition that the rotating speed of the vertical axis wind wheel is 200rpm, the input current is slowly increased from 0A, and a curve of the relation between the control current and the output torque is shown in figure 4.

From the analysis of FIG. 4, it can be seen that the current and output torque curves are fitted to obtain a polynomial equation of

y＝46.3552x⁴-51.087x³+24.044x²+4.036x+0.7832

Calculating to obtain a correlation coefficient R²0.99826, the index value is close to 1, the fitting degree and reliability are high, and curve trend can be expressed.

Under the condition that the rotating speed of the vertical axis wind wheel is 200rpm, the input current is decreased progressively, and the relation curve of the control current and the output torque is shown in figure 5.

From the analysis of FIG. 5, it can be seen that the current and output torque curves are fitted to obtain a polynomial equation of

y＝-39.5455x⁴+65.1635x³-46.0189x²+24.6793x+0.7798

Calculating to obtain a correlation coefficient R²0.99815, a curve trend can be expressed.

Under the condition that the rotating speed of the vertical axis wind wheel is 600rpm, the input current is slowly increased from 0A, and a relation curve of the control current and the output torque is shown in figure 6;

from the analysis of FIG. 6, the current and output torque curves are fitted to obtain a polynomial equation of

y＝-1.7043x⁴+16.9763x³-8.4746x²+10.6094x+0.7826

Calculating to obtain a correlation coefficient R²0.99834, a curve trend can be expressed.

Under the condition that the rotating speed of the vertical axis wind wheel is 600rpm, the input current is decreased progressively, and the relation curve of the control current and the output torque is shown in figure 7;

from the analysis of FIG. 7, it can be seen that the current and output torque curves are fitted to obtain a polynomial equation of

y＝-163.2443x⁴+243.84548x³-128.2756x²+38.1478x+0.8021

Calculating to obtain a correlation coefficient R²0.99795, a curve trend can be expressed.

From the above graph analysis, it is known that the input current and output torque are not perfectly linear, thereby affecting the use of magnetic particle brakes. The method provides a basis for realizing the precise loading of the magnetic powder brake applied to the universal test bed device for the performance detection of the vertical axis wind wheel.

In this embodiment, a magnetic powder brake with a model number fz25.k is used as a research object, and the relevant parameters are as follows: the rated torque is 25 N.m, the slip power is 600w, the rated current is 0.8A, and the allowable rotating speed is 1500 r/min. The output torque of the magnetic powder brake can stop the vertical axis wind wheel rotating under the action of wind power when the input current is increased to a certain value. The rated torque refers to the braking torque generated by the magnetic powder brake under the excitation current, and in the performance experiment of the vertical axis wind turbine vertical axis wind wheel, when the magnetic powder brake is selected, the magnetic powder brake with the rated torque larger than the maximum torque (generally starting torque) of the vertical axis wind wheel is selected.

The above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and it should be understood by those skilled in the art that the specific embodiments of the present invention can be modified or substituted with equivalents with reference to the above embodiments, and any modifications or equivalents without departing from the spirit and scope of the present invention are within the scope of the claims of the present invention.