CN104819098B - A kind of wind-power electricity generation maximum power tracking method of Speedless sensor - Google Patents

Abstract

The invention discloses a method for tracking the maximum power of wind power generation without a speed sensor. The steps are as follows: 1) obtaining the relationship curve between the maximum wind energy capture and the motor speed through experiments; 2) modeling and analyzing the electromagnetic torque of the generator ;3) Analyze the transmission chain model in the state of maximum power tracking; 4) Determine the relationship between the optimal output power and the synchronous speed of the induction motor, and establish a look-up table; 5) Design an adaptive controller for the system. The invention can realize the maximum power tracking of the wind power generator at low wind speed without measuring the speed of the wind power generator and the size and direction of the wind force. Because the magnitude and direction of the wind are affected by various reasons, it is difficult to ensure that it remains constant, and the accurate measurement process is complicated and increases the system cost. Therefore, the present invention effectively solves the measurement difficulties faced by the conventional wind power generation system when it needs to measure the magnitude and direction of wind force, and reduces the system cost to a certain extent.

Description

A wind power generation maximum power tracking method without speed sensor

technical field

The invention relates to the field of maximum power tracking control of a wind power generation system, in particular to a control method for maximum power tracking that does not require a speed sensor.

Background technique

Wind is difficult to keep constant in space and time, coupled with its unpredictability and intermittent nature, the full utilization of wind energy faces many challenges. At present, variable-speed fixed-pitch systems are mostly used in wind power generation systems. The wind energy obtained by the fan is related to the ratio of the tip speed of the wind rotor to the wind speed (tip speed ratio). When the wind speed is low, the purpose of the control is to adjust the speed of the fan through the power electronic device as the wind speed changes, so that the blade tip ratio is at the optimum value, so as to ensure the maximum wind energy captured by the fan and the highest power generation efficiency.

The existing maximum power tracking control methods for wind power generation systems mainly include the following types:

1) Direct speed control method: As the wind speed changes, measure the wind speed and the fan speed, and adjust the fan speed to keep the blade tip ratio constant and the best constant value, so as to achieve the purpose of maximum power tracking. For this method to work normally, it is an indispensable process to measure the wind speed and the fan speed, but it is difficult to measure the wind speed accurately, and the use of speed sensors increases the operating cost of the system.

2) Disturbance observation method (climbing method): Appropriately disturb the speed of the fan △ω _w and then observe the change of the mechanical power obtained by the fan △P _w until (△P _w /△ω _w )=0, at this time the fan Maximum wind energy captured. Although this control strategy does not require prior knowledge of the various parameters of the fan and the maximum wind energy that the fan can obtain at different wind speeds, this control is only suitable for small inertia fan systems. For fan systems with medium or large inertia, The speed of the fan cannot change rapidly with the change of the wind speed, resulting in a decrease in the control effect, and a speed sensor is also required, which increases the operating cost.

3) Power feedback method (optimal power-speed curve method): This strategy first needs to obtain the relationship curve between the maximum wind energy capture and the fan speed. The purpose of control is to determine the maximum wind energy capture of the fan by measuring the fan speed, as a control the benchmark value of the device. Although this method does not need to measure the wind speed, it faces the problem of measuring the fan speed and the maximum output power of the fan. It can only be in the suboptimal state of maximum power tracking, and can basically achieve the purpose of maximum power tracking.

Contents of the invention

Aiming at the above-mentioned deficiencies in the prior art, the present invention provides a method for tracking the maximum power of wind power generation without a speed sensor that reduces the cost of the control system.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A wind power generation maximum power tracking method without a speed sensor, the method comprising the steps of:

1) Obtain the relationship curve between the maximum wind energy capture and the motor speed through experiments:

The relationship between the aerodynamic power captured by the wind rotor and the fan speed is

The relationship between the mechanical torque of the fan and the fan speed is

Among them, P _wopt is the maximum capture power, ω _wopt is the optimal fan speed corresponding to P _wopt , ρ is the air density; R is the radius of the impeller rotation plane, C _p (λ _opt ) is the wind energy corresponding to the optimal tip ratio Utilization factor, λ=ω _w R/ν is the tip speed ratio, ω _w is the angular velocity of the fan, and ν is the wind speed;

Variable-speed fixed-pitch wind power generation system, adjust the fan speed according to the wind speed so that the tip ratio of the fan is at the optimum value, the fan can achieve the maximum wind energy capture, and the maximum wind energy that can be captured is proportional to the cube of the fan speed;

2) Modeling and analysis of generator electromagnetic torque:

The electromagnetic torque of the generator is

Among them: ω _s is the synchronous speed of the generator, r _r is the rotor resistance of the generator, I _r (ω _s ) is the rotor current of the generator, s is the slip ratio of the generator, and the rotational speed of the generator is represented by ω _r , Then s is expressed as

The variables related to the electromagnetic torque of the generator are only ω _s and ω _r , so the electromagnetic torque of the generator is expressed as T _e (ω _s ,ω _r );

3) Analyze the transmission chain model in the state of maximum power tracking:

Since the generator is connected with the transmission mechanism, if the static and viscous friction are ignored, the equation of the high-speed shaft is expressed as

In the formula, J is the moment of inertia of the high-speed shaft of the fan; T _mec is the mechanical torque of the fan; T _e is the electromagnetic torque of the generator,

It can be known from formula (5) that when the wind power generation system operates stably in the maximum power tracking state, then T _mec , T _e (ω _s ,ω _r ) satisfy

It can be seen from formula (1) and formula (2) that when the capture power P _wopt is known, the optimal fan speed ω _wopt and the optimal torque T _mecopt of the fan can be determined, and there is a one-to-one correspondence between the two; through the formula (6 ) and the known T _mecopt , ω _ropt can determine the optimal synchronous speed ω _s of the generator, and finally determine the relationship between the mechanical torque and the synchronous speed of the generator during maximum power tracking of the generator, namely T _meopt (ω _s ) ;

4) Determine the relationship between the optimal output power and the synchronous angular velocity of the induction motor, and establish a lookup table:

The relationship between the optimal power generation of the wind turbine and the electromagnetic torque and speed of the generator is expressed as

P _ωopt (ω _sopt )＝T _meopt (ω _sopt )×ω _ropt (T _meopt ) (7)

When the angular velocity of the input power supply is ω _e and the synchronous angular velocity of the corresponding generator is ω _s , due to the existence of mechanical loss and copper loss, the output electric power of the generator is P _gopt satisfying the following formula

P _gopt ＝P _wopt (ω _sopt )-P _mech-less -3r _s |I _s | ² -3r _r |I _r | ² (8)

Among them: 3r _s |I _s | ² , 3r _r |I _r | ² are the copper losses on the stator and rotor of the generator respectively, and P _mech-less is the mechanical loss. Substituting different ω _sopt into formula (8) can be The maximum output power P _gopt of the generator is obtained, and then the relationship between P _gopt and ω _s can be determined, and the relationship between them can be stored in the table one by one to establish a lookup table.

The beneficial effect of the invention is that the invention can realize the maximum power tracking of the wind generator at low wind speed without measuring the rotational speed of the wind generator and the magnitude and direction of the wind force. Because the magnitude and direction of the wind are affected by various reasons, it is difficult to ensure that it remains constant, and the accurate measurement process is complicated and increases the cost of the system. Therefore, the present invention effectively solves the measurement difficulties faced by the conventional wind power generation system when it needs to measure the magnitude and direction of wind force, and reduces the system operating cost to a certain extent.

Description of drawings

Figure 1 is a schematic diagram of maximum power tracking of wind power generation without a speed sensor;

Figure 2 is the relationship curve between the maximum captured power and the fan speed;

Figure 3 is an equivalent model of an induction motor;

Fig. 4 is the schematic diagram of the establishment process of look-up table;

Fig. 5 is the control diagram of the maximum power tracking circuit of wind power generation without speed sensor;

Fig. 6 is a schematic diagram of maximum power tracking analysis when the wind speed is a given value.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

A wind power generation maximum power tracking method without a speed sensor, its principle is as shown in Figure 1, and the method comprises the following steps:

1) Obtain the relationship curve between the maximum wind energy capture and the motor speed through experiments:

According to the aerodynamic theory, the aerodynamic power captured by the wind wheel can be expressed as

In the formula: ρ is the air density; R is the radius of the impeller rotation plane; C _p (λ, β) is the wind energy utilization coefficient of the wind turbine; β is the pitch angle; ν is the wind speed; λ=ω _w R/ν is the blade tip Speed ratio, ω _w is the angular velocity of the fan. In the maximum power tracking stage, generally only the fan speed is adjusted, while the pitch angle remains unchanged. The purpose of the control at this stage is to change the angular velocity of the fan accordingly with the change of the wind speed, so that the λ value is at the optimal blade tip ratio, and the wind energy utilization coefficient C _p (λ, β) remains unchanged;

The relationship between the aerodynamic power captured by the wind rotor and the fan speed is

The relationship between the mechanical torque of the fan and the fan speed is

Among them, ω _wopt is the optimal fan speed corresponding to the captured power P _wopt , and C _p (λ _opt ) is the wind energy utilization coefficient corresponding to the optimal blade tip ratio. The relationship curve between the maximum captured power and the fan speed is shown in Figure 2. It can be known from formula (2) and formula (3) that both P _wopt and T _mecopt are monotonously increasing functions about ω _wopt and correspond to ω _wopt one-to-one.

The variable-speed fixed-pitch wind power generation system adjusts the fan speed according to the wind speed so that the tip ratio of the fan is at an optimal value, and the fan can achieve the maximum wind energy capture, and the maximum wind energy that can be captured is proportional to the cube of the fan speed.

2) Modeling and analysis of generator electromagnetic torque:

When the asynchronous motor is running below the base frequency, if the magnetic flux is too weak, the motor core will not be fully utilized; if the magnetic flux is large, the core will be saturated to generate excessive excitation current, and in severe cases, the motor will be damaged due to overheating of the winding. Therefore, the stator terminal voltage usually adopts a constant voltage frequency ratio control method, that is, keeps V _S /ω _e unchanged, where V _S stator terminal voltage, ω _e is the angular velocity of the stator terminal power supply. ω _s is the synchronous speed of the generator, and it satisfies ω _s =2ω _e /n _p , and n _p represents the number of electromagnetic pole pairs. Therefore, if the stator terminal voltage adopts the constant voltage frequency ratio control method, V _S /ω _s will also remain unchanged, and the stator terminal voltage V _S can be expressed as V(ω _s ).

The equivalent model of the induction motor is shown in Fig. 3, where _Ir is the _rotor current of the equivalent circuit, and Is is the stator current of the equivalent circuit, which can be expressed as

The electromagnetic torque of the generator is expressed as

Among them: ω _s is the synchronous speed of the generator, r _r is the rotor resistance of the generator, I _r (ω _s ) is the rotor current of the generator, s is the slip ratio of the generator, and the rotational speed of the generator is represented by ω _r , Then s is expressed as

From the above formula (4), formula (5), formula (6) and formula (7), it can be seen that the variables related to the electromagnetic torque of the generator are only ω _s and ω _r , and the electromagnetic torque of the generator can be expressed as T _e (ω _s ,ω _r ).

3) Analyze the transmission chain model in the state of maximum power tracking:

Since the generator is connected with the transmission mechanism, if the static and viscous friction are ignored, the equation of the high-speed shaft is expressed as

In the formula, J is the moment of inertia of the high-speed shaft of the fan; T _mec is the mechanical torque of the fan; T _e is the electromagnetic torque of the generator.

According to the analysis of the transmission chain of the generator system according to the dynamic theory, in the case of maximum power tracking, only when the optimal mechanical torque T _mecopt of the fan and the electromagnetic torque T _e of the generator are equal in magnitude and opposite in direction, the power generation system Only then can it run stably in the maximum power tracking state. It can be known from formula (8) that when the wind power generation system operates stably in the maximum power tracking state, then T _mec , T _e (ω _s ,ω _r ) satisfy

From formula (2) and formula (3), it can be seen that when the capture power P _wopt is known, the optimal fan speed ω _wopt and the optimal torque T _mecopt of the fan can be determined, and there is a one-to-one correspondence between them; through formula (9) As well as the known T _mecopt , ω _ropt can determine the current optimal synchronous speed ω _s of the generator, that is, the relationship between the mechanical torque and the synchronous speed of the generator during maximum power tracking of the generator can be finally determined, that is, T _meopt (ω _s ).

4) Determine the relationship between the optimal output power and the synchronous angular velocity of the induction motor, and establish a lookup table:

The relationship between the optimal power generation of the wind turbine and the electromagnetic torque and speed of the generator is

P _ωopt (ω _sopt )＝T _meopt (ω _sopt )×ω _ropt (T _meopt ) (10)

When the angular velocity of the input power supply is ω _e and the synchronous angular velocity of the corresponding generator is ω _s , due to the existence of mechanical loss and copper loss, the output power of the fan is P _gopt satisfying the following formula

P _gopt ＝P _wopt (ω _sopt )-P _mech-less -3r _s |I _s | ² -3r _r |I _r | ² (11)

Among them: 3r _s |I _s | ² , 3r _r |I _r | ² are the copper loss on the fan stator and rotor respectively, P _mech-less is the mechanical loss, and the mechanical loss P _mech-less is related to the speed and the parameters of the generator relevant. Substituting different ω _sopt into equation (11) can obtain the maximum output power P _gopt of the generator, and then determine the relationship between P _gopt and ω _s , and store the relationship between them in the table one by one, and finally establish their relationship One-to-one correspondence between the discrete array, the establishment of a lookup table, the whole process is shown in Figure 4.

The present invention also designs an adaptive controller for the maximum power tracking method of wind power generation without a speed sensor, and the basic algorithm for adaptively adjusting the synchronous speed is

ω _s (k)=ω _s (k-1)+△ω _s (k) (12)

In the formula: k is the sequence number of the adaptive cycle; As a gain, it can scale and adaptively adjust the synchronous speed ω _s step size, and improve the rapidity of control. in

In the formula, n is the number of sampling in the adaptive cycle.

The maximum power tracking circuit control of wind power generation without speed sensor is shown in Figure 5. Now, its working principle is analyzed to a certain extent. When the wind speed is a given value, the relationship between wind energy capture and fan speed, fan torque and fan speed The relationship curve and the relationship curve between the electromagnetic torque of the generator at different synchronous speeds and the equivalent speed of the generator on the left side of the transmission chain are shown in Figure 6. When the fan runs at OP1, the synchronous speed of the generator is ω _s1 . By adjusting the frequency of the grid-side power supply of the generator, ω _s increases at an appropriate speed between ω _s1 and ω _sopt . Since T _e < T _w , the fan accelerates until it reaches the optimal speed. Similarly, when the fan runs at OP2, the synchronous speed of the generator is ω _s2 . By adjusting the frequency of the grid-side power supply of the generator, ω _s decreases at an appropriate speed between ω _s2 and ω _sopt . Since T _e > T _w , the fan decelerates until it reaches the optimal speed.

Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be carried out Modifications or equivalent replacements without departing from the spirit and scope of the technical solution of the present invention shall be covered by the claims of the present invention.

Claims (1)

1. a wind power generation maximum power tracking method without speed sensor, is characterized in that, the method comprises the steps: 1) Obtain the relationship curve between the aerodynamic power captured by the wind wheel and the motor speed through experiments: The relationship between the aerodynamic power captured by the wind rotor and the fan speed is <mrow> <msub> <mi>P</mi> <mrow> <mi>w</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msup> <mi>&amp;rho;&amp;pi;R</mi> <mn>5</mn> </msup> <msub> <mi>C</mi> <mi>p</mi> </msub> <mrow> <mo>(</mo> <msub> <mi>&amp;lambda;</mi> <mrow> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> <mo>)</mo> </mrow> </mrow> <mrow> <mn>2</mn> <msup> <mi>&amp;lambda;</mi> <mn>3</mn> </msup> </mrow> </mfrac> <msubsup> <mi>&amp;omega;</mi> <mrow> <mi>w</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> <mn>3</mn> </msubsup> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> </mrow> The relationship between the mechanical torque of the fan and the fan speed is <mrow> <msub> <mi>T</mi> <mrow> <mi>m</mi> <mi>e</mi> <mi>c</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mfrac> <msub> <mi>P</mi> <mrow> <mi>w</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>&amp;omega;</mi> <mrow> <mi>w</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>2</mn> <mo>)</mo> </mrow> </mrow> Among them, P _wopt is the aerodynamic power captured by the wind rotor, ω _wopt is the optimal fan speed corresponding to P _wopt , ρ is the air density; R is the radius of the impeller rotation plane, C _p (λ _opt ) is the optimal tip speed ratio The corresponding wind energy utilization coefficient, λ=ω _w R/ν is the blade tip speed ratio, ω _w is the angular velocity of the fan, and ν is the wind speed; Variable-speed fixed-pitch wind power generation system adjusts the fan speed according to the wind speed so that the fan blade tip speed ratio is at the optimum value, and the fan can achieve the maximum wind energy capture, and the maximum wind energy that can be captured is proportional to the cube of the fan speed; 2) Modeling and analysis of generator electromagnetic torque: The electromagnetic torque of the generator is expressed as <mrow> <msub> <mi>T</mi> <mi>e</mi> </msub> <mo>=</mo> <mfrac> <mrow> <mn>3</mn> <mo>|</mo> <msub> <mi>I</mi> <mi>r</mi> </msub> <mrow> <mo>(</mo> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> <mo>)</mo> </mrow> <msup> <mo>|</mo> <mn>2</mn> </msup> <msub> <mi>r</mi> <mi>r</mi> </msub> <mo>/</mo> <mi>s</mi> </mrow> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> Among them: ω _s is the synchronous speed of the generator, r _r is the rotor resistance of the generator, I _r (ω _s ) is the rotor current of the generator, s is the slip ratio of the generator, and the rotational speed of the generator is represented by ω _r , Then s is expressed as <mrow> <mi>s</mi> <mo>=</mo> <mfrac> <mrow> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> <mo>-</mo> <msub> <mi>&amp;omega;</mi> <mi>r</mi> </msub> </mrow> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>4</mn> <mo>)</mo> </mrow> </mrow> The variables related to the electromagnetic torque of the generator are only ω _s and ω _r , and the electromagnetic torque of the generator is expressed as T _e (ω _s ,ω _r ); 3) Analyze the transmission chain model in the state of maximum power tracking: Since the generator is connected with the transmission mechanism, if the static and viscous friction are ignored, the equation of the high-speed shaft of the fan is expressed as <mrow> <mi>J</mi> <mfrac> <mrow> <msub> <mi>d&amp;omega;</mi> <mi>r</mi> </msub> </mrow> <mrow> <mi>d</mi> <mi>t</mi> </mrow> </mfrac> <mo>=</mo> <msub> <mi>T</mi> <mrow> <mi>m</mi> <mi>e</mi> <mi>c</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>T</mi> <mi>e</mi> </msub> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>5</mn> <mo>)</mo> </mrow> </mrow> In the formula, J is the moment of inertia of the high-speed shaft of the fan; T _mecopt is the mechanical torque of the fan; T _e is the electromagnetic torque of the generator; It can be known from formula (5) that when the wind power generation system operates stably in the maximum power tracking state, then T _mecopt , T _e (ω _s ,ω _r ) satisfy <mrow> <msub> <mi>T</mi> <mrow> <mi>m</mi> <mi>e</mi> <mi>c</mi> <mi>o</mi> <mi>p</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mo>-</mo> <msub> <mi>T</mi> <mi>e</mi> </msub> <mrow> <mo>(</mo> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> <mo>,</mo> <msub> <mi>&amp;omega;</mi> <mi>r</mi> </msub> <mo>)</mo> </mrow> <mo>=</mo> <mo>-</mo> <mfrac> <mrow> <mn>3</mn> <mo>|</mo> <msub> <mi>I</mi> <mi>r</mi> </msub> <mrow> <mo>(</mo> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> <mo>)</mo> </mrow> <msup> <mo>|</mo> <mn>2</mn> </msup> <msub> <mi>r</mi> <mi>r</mi> </msub> </mrow> <mrow> <msub> <mi>&amp;omega;</mi> <mi>s</mi> </msub> <mo>-</mo> <msub> <mi>&amp;omega;</mi> <mi>r</mi> </msub> </mrow> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>6</mn> <mo>)</mo> </mrow> </mrow> According to formula (1) and formula (2), when the aerodynamic power P _w o _pt captured by the wind rotor is known, the optimal fan speed ω _wopt and the mechanical torque T _mecopt of the fan can be determined, and there is a one-to-one correspondence between them ; Through the formula (6) and the known T _mecopt , ω _r can determine the synchronous speed ω _s of the current generator, that is, the relationship between the mechanical torque of the fan and the synchronous speed of the generator can be finally determined when the maximum power of the generator is tracked That is T _mecopt (ω _s ); 4) Determine the relationship between the optimal output power and the synchronous angular velocity of the induction motor, and establish a lookup table: The relationship between the aerodynamic power captured by the wind wheel and the mechanical torque and speed of the fan is P _ωopt (ω _s )＝T _mecopt (ω _s )×ω _r (T _mecopt ) (7) When the angular velocity of the input power supply is ω _e and the corresponding synchronous speed of the generator is ω _s , due to the mechanical loss and copper loss, the output power of the fan is P _gopt satisfying the following formula P _gopt ＝P _wopt (ω _s )-P _mech-less -3r _s |I _s | ² -3r _r |I _r | ² (8) Among them: 3r _s |I _s | ² , 3r _r |I _r | ² are the copper loss on the fan stator and rotor respectively, P _mech-less is the mechanical loss, and substituting different ω _s into formula (8) respectively can be obtained The output electric power P _gopt of the fan, and then the relationship between P _gopt and ω _s can be determined, and the relationship between them can be stored in a table one by one to establish a lookup table.