CN104917201B - Double-fed blower fan active power and frequency control device and method that simulation inertia is combined with hypervelocity - Google Patents

Abstract

The invention discloses an active frequency controller and a method for a doubly-fed fan combined with simulated inertia and overspeed, comprising: a frequency deviation detection module, a DC blocking module, an adjustment variable setting module, a delay module and a speed protection module connected in sequence; The real-time power grid frequency signal and the frequency setting value are respectively input into the frequency deviation detection module to obtain the frequency deviation signal of the power grid at this time; The protection module enables the DFIG unit to exit the frequency regulation when the speed is abnormal, and the frequency regulation can be re-entered after a certain time delay. Beneficial effects of the invention: large-scale doubly-fed wind power grid-connected to replace conventional synchronous generators will reduce system inertia and deteriorate system frequency transient stability. The integrated frequency controller proposed by the invention can effectively improve this problem.

Description

Active frequency controller and method for doubly-fed fan combined with simulated inertia and overspeed

technical field

The invention relates to the technical field of doubly-fed wind power generators, in particular to a doubly-fed wind turbine active frequency integrated controller and method that combines simulated inertia and overspeed method control.

Background technique

As the most mature new energy power generation method with the most conditions for large-scale development at present, wind power generation has an increasing penetration rate in the power system, especially in regions rich in wind energy resources. The rapid development of wind power generation has brought huge environmental and economic benefits, but it also brings new challenges to the safe and stable operation of the power system.

Doubly fed induction generation (DFIG) has the characteristics of high power generation efficiency and small inverter capacity, and has become one of the main models of large wind farms. While its power electronic converter achieves maximum power tracking, it also eliminates the coupling relationship between the rotor speed and the grid frequency, and cannot release or store kinetic energy through the rotor to damp system frequency changes like traditional synchronous generators, that is, wind turbines The kinetic energy of the rotor is completely "hidden" by the frequency converter. From the perspective of the whole system, the moment of inertia of wind turbines is zero, and the large-scale connection of wind farms based on DFIG units will significantly weaken the frequency dynamic response characteristics of the system. And when it operates in the Maximum Power Point Tracking (MPPT) mode, its efficiency has been maximized, so it cannot participate in the primary frequency regulation of the system.

In order to reduce the impact of large-scale DFIG unit access on grid frequency stability, common improvement methods include:

1. Utilize the kinetic energy stored in the rotor for short-term frequency modulation, and add an active frequency control link to simulate the frequency response characteristics of the synchronous generator, so that the variable speed fan has a certain virtual inertia;

2. Reduce the efficiency of the generator by overspeeding or changing the pitch angle, so that it has spare power to participate in the primary frequency regulation of the system;

3. The method of using flywheels, battery packs and other energy storage systems to assist wind farms to participate in system frequency adjustment has also attracted the attention of many researchers.

The DFIG unit has a large inertia and a wide range of speed adjustment, so the above method can theoretically simulate a larger "simulated inertia" than the synchronous motor; however, the kinetic energy that the DFIG unit can provide is limited when the speed is low, and the speed recovery process after exiting frequency regulation The reduction of output power will cause a secondary drop in grid frequency, and the deviation of the operating point from the maximum power tracking point during frequency regulation will also aggravate this adverse effect. Moreover, the perfect frequency regulation capability of wind farms requires wind turbines to have both controllable inertial response and primary frequency regulation capability. The integrated control method that organically combines primary frequency regulation and inertial control after load shedding is relatively rare.

Contents of the invention

In order to solve the above problems, the present invention provides an active frequency controller and method for a doubly-fed fan combined with simulated inertia and overspeed. This method enables the double-fed fan to use the rotor kinetic energy and load shedding reserve capacity to effectively support the inertial frequency modulation of the system, reduce the static frequency error, and avoid the secondary impact of the system frequency that may be caused by excessive frequency modulation.

In order to achieve the above object, the present invention adopts the following technical solutions:

An active frequency controller for a doubly-fed fan combining simulated inertia and overspeed, comprising: a frequency deviation detection module, a DC blocking module, an adjustment variable setting module, a time delay module and a speed protection module connected in sequence;

The real-time power grid frequency signal f _mea and the frequency setting value f _ref are respectively input into the frequency deviation detection module to obtain the frequency deviation signal Δf of the power grid at this time; Δf obtains the speed adjustment amount; the speed protection module makes the DFIG unit quit the frequency regulation when the speed is abnormal, and re-enter the frequency regulation after a certain time delay.

A control method for a doubly-fed fan active frequency controller that simulates inertia and overspeed, comprising the following steps:

(1) Determine the maximum wind power captured by the DFIG, and obtain the maximum power tracking curve equation of the DFIG;

(2) When the grid frequency is working normally, the wind turbine operates in the state of overspeed and load reduction, and the stored kinetic energy of the rotor is increased by the overspeed method to obtain the frequency modulation reserve capacity;

(3) When it is detected that the system frequency deviation exceeds the control dead zone, the speed adjustment amount is determined according to the frequency deviation, the rotor speed, and the overspeed load shedding amount. The double-fed wind turbine determines the given output active power reference according to the speed adjustment amount and the rotor speed value.

(4) Adjust the static error adjustment coefficient when the double-fed wind turbine participates in the primary frequency regulation of the system, so that it has the same droop characteristics as the traditional generator;

The maximum wind power captured by the wind generator in the step (1) is:

Among them, P _opt is the maximum power captured by the wind turbine at a given wind speed, ρ is the air density, C _opt is the optimal wind energy conversion rate coefficient related to the blade tip speed ratio λ _opt and the pitch angle β, and A is the fan sweep The area of , U _w is the wind speed, w _topt is the rotational angular velocity of the fan, and R is the radius of the blade.

In the step (1), the maximum power tracking curve equation of the doubly-fed wind power generator is specifically:

In the formula:

In the formula: P _opt is the maximum power captured by the wind turbine, k _opt is the power tracking coefficient determined by the aerodynamics of the wind turbine, ρ is the air density, C _Popt is the optimal power conversion coefficient, and λ _opt is the optimal blade tip speed Ratio, R is the radius of the blade, ω _r is the rotor speed, p is the number of pole pairs of the generator, G is the transmission coefficient of the gearbox, and w _t is the rotational angular velocity of the fan.

The rotational speed adjustment in the described step (3) is:

Among them, k _opt k _de is the power tracking coefficient before and after load shedding, d% means the amount of load shedding, w _r is the rotor speed, Δf is the frequency deviation, f _b f _a is the upper and lower limits of power grid frequency regulation under normal conditions, Usually the power grid frequency drop is not allowed to exceed 0.5Hz.

Beneficial effects of the present invention:

1. Large-scale doubly-fed wind power grid-connected to replace conventional synchronous generators will reduce system inertia and deteriorate system frequency transient stability. The integrated frequency controller proposed by the present invention can effectively improve this problem.

2. The comprehensive frequency modulation control method combining analog inertia control and overspeed method proposed by the present invention has the characteristics of perfect frequency modulation function and stable frequency modulation process, and can effectively reduce the frequency fluctuation amplitude and static frequency error caused by load disturbance. The control quantity setting method proposed by further research makes the DFIG unit participate in the frequency regulation process to have the same droop characteristics as the traditional generator.

3. Through the simulation analysis, it is verified that after the DFIG unit adopts the speed regulation integrated controller, the system frequency characteristics are effectively improved. During the frequency modulation process, the speed is maintained in a safe area, which overcomes the problems of short frequency modulation time and easy machine cut-off of the general kinetic energy control method.

Description of drawings

Figure 1 is a schematic diagram of a typical analog inertia comprehensive control method;

Figure 2 is the droop frequency control characteristic curve of a conventional generator with a governor;

Figure 3 is a schematic diagram of DFIG load reduction under the same wind speed;

Fig. 4 is the comprehensive control principle diagram of DFIG rotational speed regulation of the present invention;

Figure 5 is a schematic diagram of the relationship between output power, captured power and rotational speed when DFIG participates in the frequency modulation process when the load suddenly increases;

Figure 6 is a schematic diagram of power changes during deceleration and acceleration;

Fig. 7 is a schematic structural diagram of a calculation example of the simulation system of the present invention;

Fig. 8 is a comparison diagram of the system frequency response when the load L2 suddenly increases by 100MW according to the embodiment of the present invention;

Fig. 9 is the output active power change curve of the DFIG unit according to the embodiment of the present invention;

Fig. 10 is the speed change curve of the DFIG unit according to the embodiment of the present invention;

Fig. 11 is the change curve of the input mechanical power when the DFIG unit participates in the frequency regulation process according to the embodiment of the present invention.

detailed description

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

1. Analysis of inertial frequency regulation and primary frequency regulation of DF IG unit

1.1 Rotor kinetic energy control method

The kinetic energy stored in the rotor of the wind turbine is:

In the formula: J is the moment of inertia of the machine, ω is the speed. The speed adjustment range of the DFIG unit is generally synchronous speed ±0.2pu. By controlling the change of the rotor speed to release or absorb the kinetic energy of the rotor to participate in system frequency modulation, the kinetic energy increment of the rotor before and after the speed change is:

In the formula: ΔE is the kinetic energy change of the rotor, ω ₁ and ω ₂ are the rotor speed before and after frequency modulation, respectively. By adding an additional active power reference value associated with the system frequency change to the active power reference value of the DFIG rotor side converter, the variable speed fan can actively respond to the system frequency change by using the stored kinetic energy, simulating the frequency response characteristics of the conventional generator . The dotted line box in Figure 1 below is a typical analog inertial frequency controller. The complete additional active frequency controller also includes auxiliary control modules such as a speed protection module, a speed recovery module, and a coordination module with conventional units.

The active power obtained by the additional frequency controller in Figure 1 is:

Neglecting the system loss, it can be written in a form similar to the equation of motion of the conventional generator rotor:

In the formula: H _s is the inertia constant of the conventional generator, K _f is the proportional coefficient, 1/ _R is the droop coefficient, Δf is the system frequency variation, PM is the input mechanical torque of the wind turbine, and _PE is the output electromagnetic torque , D is the load damping coefficient. It can be seen from formula (1) that when K _f is greater than zero, it can produce a moment of inertia similar to that of a traditional generator, and when 1/R is greater than zero, the damping coefficient can be increased to improve the frequency dynamic response performance.

When the system frequency changes suddenly, the simulated inertial control makes full use of the characteristics of DFIG that can quickly adjust the active power output, and uses the kinetic energy stored in the rotor to enable the wind turbine to provide short-term active power support and improve the transient stability of the system frequency. However, because there is no active power reserve capacity, it cannot continuously provide frequency regulation for the system. When the fan speed is lower than the threshold value, it will exit frequency regulation and enter the speed recovery stage.

1.2 Load shedding control method

Conventional generators can adjust the input mechanical power by changing the opening of the intake valve through the governor, so that the generator can participate in primary frequency modulation. Conventional generators with governors have drooping characteristics, and their output power increments are shown in Figure 2 and The frequency deviation is proportional to the relationship, namely:

ΔP＝-K _G *Δf

In the formula, K _G is the unit regulation power of the unit, and the reciprocal of K _G is the static adjustment coefficient of the conventional generator set, namely:

In order to have the same droop frequency regulation characteristics, the DFIG unit should have a certain reserve capacity when it is in the maximum power tracking operation mode, otherwise it can only play a role when the frequency increases, but cannot play a role when the frequency decreases. There are two feasible methods to obtain reserve capacity: one method is the overspeed method, so that the operating speed during normal operation is greater than the optimal speed during maximum power tracking to reduce the efficiency of the wind turbine, and then control the speed to decrease when the output power needs to be increased Make the fan capture more mechanical power; another method is to increase the pitch angle of the fan to reduce the captured wind power. Figure 3 below is a schematic diagram of load shedding control:

The overspeed method is based on AC frequency conversion control technology, and the control speed is much faster than the pitch angle control speed. It is mainly limited by the maximum speed and has a certain control blind zone, so it is suitable for areas below the rated wind speed. The actuator of the pitch control method is a mechanical component, and the pitch angle adjustment speed is relatively slow, so the effect of the wind turbine with direct pitch angle control participating in frequency modulation is not obvious, and the frequent action of the pitch system increases the mechanical loss and increases the maintenance cost It is easy to shorten the service life of the fan. Therefore, when conditions permit, the method of overspeed is given priority to obtain spare capacity.

2. Comprehensive control of DFIG unit speed adjustment

The wind farm has inertial response capability, which can reduce the system frequency change rate and improve the transient stability of the system frequency. It has standby active power, which can increase/decrease the input mechanical power to participate in the primary frequency regulation of the system. Therefore, a perfect wind farm frequency regulation strategy should Both of these abilities are present at the same time. As mentioned above, the wind turbine can obtain the reserve capacity through the overspeed method and the pitch method, and the method of combining the pitch method with the simulated inertia is obviously limited by the defects of the pitch method itself. The overspeed method is mainly limited by the extreme speed value. According to the operation statistics of the wind power department, the probability that the fan output power exceeds 80% of the rated value generally does not exceed 10% of the running time, so overspeed control is applicable in most cases. The increase of the rotating speed also enables the fan to store more kinetic energy that can be used for frequency regulation, so the present invention adopts the method of combining the overspeed method and the analog inertia control.

2.1 Comprehensive control principle of speed regulation and dynamic process analysis of frequency regulation

The maximum wind power captured by the wind turbine can be expressed as:

In the formula: P _opt is the maximum power captured by the wind turbine at a given wind speed, ρ is the air density, C _opt is the optimal wind energy conversion rate, λ _opt is the optimal tip speed ratio, β is the pitch angle, and A is the wind turbine The swept area, U _w is the wind speed. Blade tip speed ratio λ _opt =w _topt R/U _w , w _topt is the rotational angular velocity of the fan, and R is the blade radius.

Since it is difficult to accurately detect the wind speed in actual operation, the corresponding optimal speed cannot be directly given, so the closed-loop control of the speed is generally not directly adopted, but the indirect control of the speed is achieved by controlling the balance between the input mechanical power and electromagnetic power. control. Under the condition of not considering the loss, the current rotor speed ω _r of the DFIG unit uniquely determines P _opt as the active reference value _Pref in the rotor-side active power control system. Adjusting the speed can directly and conveniently adjust the output power. From formula (2), the maximum power tracking curve equation can be obtained as:

In the formula:

In the formula: _kopt is a constant determined by the aerodynamics of the wind turbine, usually given by the manufacturer, p is the number of pole pairs of the generator, and G is the transmission coefficient of the gearbox.

Figure 4 shows the functional block diagram of the controller: when the grid frequency is normal, the wind turbine is running in the state of overspeed and load reduction. When it is detected that the system frequency deviation exceeds the control dead zone, according to (5) formula The output speed adjustment Δw, the DFIG unit determines the given output power reference value according to (w _r +Δw).

It specifically includes: a frequency deviation detection module, a DC blocking module, an adjustment variable setting module, a delay module and a speed protection module connected in sequence;

The real-time grid frequency signal f _mea is input to the controller by detecting the grid frequency, and the frequency signal is compared with the frequency setting value f _ref to obtain the frequency deviation signal Δf of the grid at this time; the adjustment variable setting module is based on the frequency deviation signal Δf and other parameters as follows ( Equation 5) obtains the magnitude of the speed adjustment Δω; the DFIG determines the new optimal power reference value P _ref according to (w _r +Δω) and sends it to the converter on the stator and rotor side, and finally achieves the output power of the DFIG in response to the grid frequency volatility purpose. Among them: the direct blocking link can eliminate the influence of the steady-state frequency error of the power grid, so that the controller will only act when the deviation signal Δf is greater than the control dead zone. The speed protection module enables the DFIG unit to exit the frequency regulation when the speed is abnormal, and the frequency regulation can be restarted after a certain time delay.

Different from the general analog inertia control method, the speed of the adjustment process is always in the safe area, and the speed protection module only acts in the event of a fault. The delay module can prevent frequent switching during speed recovery.

Fig. 5 is a schematic diagram of the power-speed change in the whole process of frequency modulation of DFIG unit when the system load suddenly increases.

Before frequency regulation, the _DFIG unit runs at overspeed load shedding point 2. When the system frequency fluctuates greatly, the electromagnetic power immediately increases from point 2 to point 3. At this time, because the output electromagnetic power is greater than the mechanical power captured by the fan, the rotor will decelerate and release kinetic energy ; It can be seen from the figure that before the speed decreases to the optimal speed, the mechanical power captured by the fan will increase from point 2 to point 4 with _{w r} decreasing, while the electromagnetic power will decrease from point 3 to point 4 as w _r decreases ( When point 4 coincides with the MPPT point, it is the limit of the frequency modulation capability), and finally when ΔP _w = ΔP _m , the power of the generator reaches a new equilibrium state, and the output power maintains an increase of ΔP _w to participate in a frequency modulation. Under normal circumstances, Δf gradually decreases under the action of the secondary frequency regulation of the system, and Δw also decreases accordingly. Under the action of the wind turbine’s own control and adjustment, the rotor will slowly accelerate and return to the load-reduction operating point, and the acceleration process takes less time than the deceleration process. Long, avoiding the impact on the frequency of the system caused by the reduction of the output power caused by the recovery process of the fan speed.

DFIG participates in the whole process of frequency modulation, the output power changes along 2→3→4→2, and the input power changes along 2→4→2. This process not only releases the power of the sudden change of the rotor kinetic energy sharing system, but also makes full use of the spare capacity to participate in the system FM once. The frequency modulation process when the system frequency suddenly increases is opposite to the above process. Similarly, it can be seen that the rotor accelerates first, then decelerates and finally returns to the equilibrium point. The power change curve is shown in Figure 6 below:

_In Figure ₆ , the area S1 is the kinetic energy released by the rotor during deceleration, and the area S2 is the kinetic energy absorbed by the rotor during acceleration. When the acceleration area is equal to the deceleration area, the operating point finally returns to the starting point, that is:

To sum up, after adopting the comprehensive control strategy of speed adjustment, the DFIG unit releases the kinetic energy of the rotor and increases the captured mechanical power according to the fluctuation of the system frequency, effectively supporting the stability of the system frequency, thus improving the disadvantage of reducing the system inertia after the wind farm is connected to the grid. influences. Because DFIG stores more kinetic energy by increasing the speed and reserves a certain reserve capacity, the rotor speed is within the safe area during the whole frequency modulation process, so there is no risk of shutdown after the fan participates in frequency modulation. The DFIG unit needs to set a reasonable static frequency characteristic to participate in a frequency adjustment, so that it has the same droop characteristic as the traditional generator.

2.2 Analysis and control of comprehensive control characteristics

The size of the static adjustment coefficient has an important influence on maintaining the stability of the system frequency. The smaller the static adjustment coefficient is, the stronger the frequency adjustment capability of the generator set is, and it is easier to ensure frequency stability. However, in actual operation, too small static adjustment coefficient may lead to unreasonable load distribution among generator sets in the system, making the unit speed control system unable to Therefore, the DFIG unit participating in the primary frequency regulation of the system needs to adjust the adjustment coefficient reasonably. Suppose the power tracking curve equation after overspeed load shedding is:

In the formula: k _de is the load shedding power tracking coefficient. Use d% to represent the amount of load shedding, and the power relationship between the maximum power tracking point and the overspeed point is:

P ₂ =(1−d%)P ₁ (3)

Then the sag coefficient can be expressed as:

For conventional generators, the δ value is generally 3%-5%, and the frequency drop of the power system is generally not allowed to exceed 0.5Hz. Therefore, if the wind turbine has a static frequency characteristic similar to that of a general turbogenerator, the load shedding level of the unit should be 20%-33%, can be adjusted by power tracking curve. In order to make the DFIG unit have the same droop characteristics as the generator shown in Figure 2, it is necessary to control the position of the stable operating point 4 during the frequency regulation process. The position of point 4 is not easy to control directly, and the sudden increase power of control point 3 is proportional to Δf to control the position of point 4. The DFIG unit runs at the load shedding point 2 before frequency regulation, and the output power of the wind turbine unit after the frequency disturbance becomes:

In the case of a small speed adjustment range, it can be considered that w _r ＞＞Δw, so:

which is:

In the formula: ΔP _max is the limit value that can be achieved by the sudden increase power ΔP _m in Fig. 5, referred to as the limit frequency modulation power, and the limit frequency modulation power should not be too large to prevent the speed from entering the power instability region. It can be seen from Figure 5 that the limit frequency modulation power is the power difference between the maximum power tracking point (point 1) and the point on the load shedding power curve with the same speed (point 5). The power at the maximum power tracking point and the overspeed load shedding point are:

From the power relationship between the two points in formula (3), the speed relationship between the two points can be obtained:

Substituting the speed at point 5 into the load shedding power tracking curve equation can be obtained:

so:

Substituting ΔP _max into formula (4) and simplifying, we can get:

Among them, k _opt k _de is the power tracking coefficient before and after load shedding, d% means the amount of load shedding, w _r is the rotor speed, Δf is the frequency deviation, f _b f _a is the upper and lower limits of power grid frequency regulation under normal conditions, Usually the power grid frequency drop is not allowed to exceed 0.5Hz.

It can be seen from the two equations (4) and (5) that the power tracking coefficient and the frequency adjustment range are setting parameters, which can be adjusted according to the static adjustment coefficient. Within the frequency adjustment range Δf∝Δw∝ΔP, the DFIG unit participating in the primary frequency regulation of the system has the same droop characteristics as the traditional generator.

3. Simulation analysis

The present invention is based on the classic four-machine two-area system, and builds the example system shown in Figure 7 in MATLAB/Simulink, wherein G1, G3 and G4 are thermal power plants with a capacity of 400MW and 1000MW respectively, and G2 at the No. 2 node is The wind farm (the wind farm consists of 200 1.5MW doubly-fed wind generators), the rated capacity of the wind farm is 14.2% of the total system capacity. Loads L1 and L2 are constant active loads of 500MW and 1000MW respectively. The rated capacity of each power plant is selected as its power base value, and the speed base value is the rated speed of the DFIG unit.

3.1 Simulation analysis of frequency response when the system load changes suddenly

The wind speed is 9m/s, and the frequency modulation range is ±0.5Hz. The DFIG unit is in a 11% load shedding state through the overspeed method. The load L2 suddenly increases from 1000MW to 1100MW at 10.0s, resulting in a decrease in system frequency. Figure 8 shows the comparison of system frequency fluctuation curves after load disturbance when the DFIG unit adopts three control modes: no additional frequency control, general analog inertia control, and speed adjustment comprehensive control. It can be seen from the figure:

When the DFIG unit is not controlled, the frequency drops the fastest and the drop is relatively large, and the fluctuation amplitude has exceeded the requirement;

The general analog inertia control method can make the wind turbine respond to the system frequency fluctuation, and effectively suppress the maximum amplitude of the frequency fluctuation. However, due to the limited kinetic energy that can be provided by the low fan speed, the wind turbine quits the frequency regulation after about 10s, causing a secondary impact on the system frequency, and the impact effect will be intensified as the scale of the wind farm increases;

The speed adjustment comprehensive control strategy is adopted, and the frequency modulation control takes effect after the frequency deviation exceeds the frequency modulation control dead zone (±0.2Hz). In the initial stage of frequency modulation, relying on the rotor to release kinetic energy effectively suppressed system frequency fluctuations. The minimum frequency was increased from 49.38Hz to 49.66Hz, and the amplitude of frequency changes was reduced by 45.1%. The wind turbine not only suppresses fluctuations in the initial stage of system frequency drop, but also shares the unbalanced power of frequency-regulated generators for a long time during the system's primary frequency regulation process. Compared with no additional control, the static frequency deviation is reduced by about 0.05Hz. Since the overspeed method makes the generator store more kinetic energy and the operating point gradually approaches the maximum power tracking point, the DFIG unit avoids the secondary impact brought by the general analog inertia control method throughout the process, and the frequency recovery process is improved.

3.2 Analysis of active power output characteristics

Figure 9 shows the output power changes of the DFIG unit under three control modes during the frequency sudden increase disturbance process. When the DFIG unit has no additional frequency control, the wind turbine operates in the maximum wind energy tracking control mode, and its output power remains 0.225pu without responding to system frequency changes. Using the general analog inertia control method, the stored kinetic energy can be used to respond to system frequency changes, so the output power increases at the beginning of frequency modulation, but at 20s, the frequency control link is forcibly cut off because the speed is too low, which also leads to a secondary impact on the system frequency. Adopting the comprehensive control method of speed adjustment, the output power is reduced from 0.225 to 0.2pu (load reduction 11%) under normal conditions. After the frequency modulation starts, the output power responds to the system frequency change and increases rapidly, and gradually decreases with the speed and frequency deviation, but it is small. The speed is relatively slower, the final output power becomes the power before load shedding, and the reserve capacity is fully utilized, so the DFIG unit can effectively participate in the long-term frequency regulation of the system.

3.3 Analysis of speed change process

Figure 10 shows the change of speed when the DFIG unit participates in the frequency regulation process. When the DFIG unit has no additional frequency control, the wind turbine operates in the maximum wind energy tracking control mode, and the unit does not respond to system frequency changes. Its speed is only adjusted according to the change of wind speed to maintain the optimal tip speed ratio to track the maximum wind energy. In the case of general analog inertia control, the kinetic energy stored in the rotating part is limited and there is no controllable energy source. If the frequency modulation is excessive, the frequency control link will be forcibly cut off because the speed is too low, resulting in secondary fluctuations in the system frequency. When the integrated control method of speed adjustment is adopted, the speed increases from 0.85 to 1.02pu during stable operation, which stores more kinetic energy and is beneficial to frequency regulation. The final speed tends to the optimal speed rather than the lower limit of the speed, so there is no risk of cutting the machine.

3.4 Analysis of input mechanical power characteristics

Figure 11 shows the change of input mechanical power when the DFIG unit participates in the frequency regulation process. It can be seen from the figure that the wind power captured by the DFIG unit in the frequency regulation process using the general analog inertia control method has been decreasing until it exits the frequency regulation and enters the speed recovery stage. Part of the kinetic energy lost by the rotor is used for system frequency regulation and the other part is used to make up for mechanical power Loss, this factor further reduces the adjustable frequency time of the wind turbine. The DFIG unit adopts the comprehensive control method of speed regulation, and the captured wind power has been increasing by about 0.05pu during the frequency regulation process.

Through the simulation analysis, it is verified that the frequency characteristics of the DFIG unit are effectively improved after adopting the comprehensive control strategy of speed regulation. During the frequency modulation process, the speed is maintained in a safe area, which overcomes the problems of short frequency modulation time and easy machine cut-off of the general kinetic energy control method.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the scope of protection of the invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (5)

1. a kind of control method of the double-fed blower fan active power and frequency control device that simulation inertia is combined with hypervelocity, is characterized in that,

Described double-fed blower fan active power and frequency control device includes：The frequency departure detection module that is sequentially connected, every straight module, regulation Measure adjust module, time delay module and rotating speed protection module；

Real-time grid frequency signal and frequency setting value respectively incoming frequency separate-blas estimation module obtain now electrical network frequency it is inclined Difference signal；Through adjusting module into regulated quantity every straight module, regulated quantity adjusts module according to frequency departure to frequency departure signal Signal obtains rotational speed regulation amount；Rotating speed protection module makes double-fed blower fan that frequency modulation is exited under rotating speed abnormal conditions, and time delay is certain Frequency modulation is put into again after time could；

Described control method is comprised the following steps：

(1) determine the most strong wind power of double-fed blower fan capture, and obtain double-fed blower fan maximum power tracking curve equation；

(2) during mains frequency normal work, double-fed fan operation, in hypervelocity off-load state, improves rotor storage by the method that exceeds the speed limit dynamic Frequency modulation spare capacity can simultaneously be obtained；

(3) when system frequency deviation is detected more than controlling dead error, according to frequency departure size, rotor speed, hypervelocity off-load Amount determines rotational speed regulation amount, and double-fed blower fan determines the given output of double-fed blower fan according to rotational speed regulation amount and rotor speed Reference value；

(4) when participating in system primary frequency modulation to double-fed blower fan, static difference coefficient is adjusted so which has and conventional electric power generation The same droop characteristic of machine.

2. the control of the double-fed blower fan active power and frequency control device that a kind of simulation inertia as claimed in claim 1 is combined with hypervelocity Method, is characterized in that, in the step (1), the most strong wind power of the capture of double-fed blower fan is：

$\left\{\begin{array}{c}{P}_{opt}=\frac{1}{2}{\mathrm{\ρC}}_{p_{opt}}({\mathrm{\λ}}_{opt},\mathrm{\β}){\mathrm{AU}}_w^3\\ C_{p_{opt}}({\mathrm{\λ}}_{opt},\mathrm{\β})=0.22(\frac{116}{{\mathrm{\λ}}_i}-0.4\mathrm{\β}-5)e^{\frac{-12.5}{{\mathrm{\λ}}_i}}\\ \frac{1}{{\mathrm{\λ}}_i}=\frac{1}{{\mathrm{\λ}}_{opt}+0.08\mathrm{\β}}-\frac{0.035}{{\mathrm{\β}}^3+1}\\ {\mathrm{\λ}}_{opt}=\frac{w_{t_{opt}}R}{U_w}\end{array}\right.$

Wherein, P_optTo give the peak power of double-fed blower fan capture under wind speed, ρ is atmospheric density, C_optIt is and tip speed ratio λ_opt, the related optimum wind power conversion efficiency coefficient of pitch angle beta, A is the inswept area of double-fed blower fan, U_wFor wind speed, w_toptFor double-fed Blower fan angular velocity of rotation, R are blade radius.

3. the control of the double-fed blower fan active power and frequency control device that a kind of simulation inertia as claimed in claim 1 is combined with hypervelocity Method, is characterized in that, in the step (1), double-fed blower fan maximum power tracking curve equation is specially：

$P_{opt}=k_{opt}{w}_r^3$

In formula：

$k_{opt}=\frac{1}{2}\mathrm{\ρ}\left(\frac{C_{P_{opt}}}{{\mathrm{\λ}}_{opt}^3}\right){\mathrm{\πR}}^5$

${\mathrm{\ω}}_r=\left(\frac{p}{2}\right){\mathrm{G\ω}}_t$

In formula：P_optFor the peak power of double-fed blower fan capture, k_optBe determined by double-fed blower air kinetics power with Track coefficient, ρ is atmospheric density, C_PoptOptimal power conversion coefficient, λ_optFor optimum tip speed ratio, R is blade radius, ω_rTo turn Rotor speed, p be double-fed blower fan number of pole-pairs, G be gear-box carry-over factor, w_tFor double-fed blower fan angular velocity of rotation.

4. the control of the double-fed blower fan active power and frequency control device that a kind of simulation inertia as claimed in claim 1 is combined with hypervelocity Method, is characterized in that, the rotational speed regulation amount in the step (3) is：

$\mathrm{\Δ}w=\frac{k_{opt}-k_{de}}{3k_{opt}(1-d\%)}\×w_r\×\frac{\mathrm{\Δ}f}{f_b-f_a}$

Wherein, k_opt、k_deThe respectively forward and backward power tracking coefficient of off-load, d% represent off-load amount size, w_rFor rotor speed, Δ f For frequency departure amount size, f_b、f_aRespectively mains frequency adjusts upper and lower limit under normal circumstances.

5. the control of the double-fed blower fan active power and frequency control device that a kind of simulation inertia as claimed in claim 1 is combined with hypervelocity Method, is characterized in that, in order that double-fed blower fan is with the droop characteristic as conventional electric generators in the step (4), need It is directly proportional to frequency departure amount Δ f by the uprush power of uprushing of power points of control, and then the position of control stable operating point.