KR101235907B1 - Apparatus of controlling a wind power generation system and method thereof - Google Patents

Abstract

PURPOSE: A wind power generation system control device and a method thereof are provided to suppress shaft torsional generated due to difference between a generator and a blade in case of system error. CONSTITUTION: A DBR control unit generates a pulse type DBR trigger signal based on the difference between a preset threshold value and a series link voltage. The DBR control unit includes a first comparison unit(400), a proportional integral and differential calculus unit(410), a limiter(420) and a second comparison unit(430). The first comparison unit outputs the difference between the preset threshold of a series link voltage and a series link voltage. The proportional integral and differential calculus unit compensates an output value of the first comparison unit. The limiter limits output of the proportional integral and differential calculus unit to the value of the specified range. [Reference numerals] (410) Proportional integral and differential calculus unit

Description

Apparatus of controlling a wind power generation system and method

The present invention relates to a wind power generation system, and more particularly, to an apparatus and method for controlling a wind power generation system in a system accident.

There are two main types of wind power generation methods: doubly-fed induction generator (DFIG) and permanent magnet synchronous generator (PMSG). The PMSG method uses a multi-pole synchronous generator by directly driving a blade and a generator or by using a gearbox.

Line accident means a line short circuit or ground fault in the line. In the event of a system accident, the system voltage drops or the voltage disappears completely for a short time.

In the past, mechanical modeling of most PMSGs assumed that the blades, the generators, and the axis connecting them as one inertia. However, in a real system, the generator and the blades have their respective speeds, causing the shaft to twist. In case of system accident, the power output to the system decreases, so the vibration occurs due to the change of torque due to the imbalance of the generator input power and the system output power. This is called torsional vibration.

Song Seung-ho, Lim Ji-hoon, “Analysis of Grid Code and Advanced Technology of LVRT for Grid Linkage of Wind Power Generation System”, Journal of the Korean Society for Energy Research, 2008.10 pp93-97 Kim, Jung Jae, Song Seung Ho, "Development of PSCAD / EMTDC Simulation Model of Variable Speed Wind Power Generation System Using Permanent Magnet Synchronizer", Journal of the Korean Institute of Power Electronics, 2005.12, pp610-617 UNISUN, “Maximum Power Control of Permanent Magnet Variable Speed Wind Power Generator”, Unison Commission Final Report, 2003

The present invention has been made in an effort to provide a control apparatus and a method of a wind power generation system capable of suppressing axial torsional vibration caused by a difference in angular speeds of a generator and a blade in a system accident.

In order to achieve the above technical problem, an example of a control apparatus of a wind power generation system according to the present invention has a frequency greater than a resonant frequency of a wind turbine drive train based on a difference between a predetermined threshold value and a DC link voltage. A DBR controller configured to generate a pulse-shaped DBR trigger signal; And a load torque control unit performing an operation of reducing and outputting a predetermined ratio with respect to the load torque during maximum output control in accordance with the DBR trigger signal.

In order to achieve the above technical problem, an example of a control method of a wind power generation system according to the present invention has a frequency greater than a resonance frequency of a wind turbine drive train based on a difference between a predetermined threshold value and a DC link voltage. Generating a pulse-shaped DBR trigger signal; And reducing the output torque magnitude of the maximum output control by a predetermined ratio in accordance with the DBR trigger signal.

Another example of the control method of the wind power generation system according to the present invention for achieving the above technical problem, the step of determining whether the DC link voltage has reached a predetermined threshold value; When the DC link voltage reaches the threshold, determining whether a magnitude of a system voltage exceeds a predetermined division value; When the magnitude of the grid voltage exceeds the division value, the DBR control according to the DBR trigger signal and the torque control of the generator-side converter are simultaneously performed, and when the magnitude of the grid voltage does not exceed the preset division value, the generator side Performing only torque control of the converter.

According to the present invention, it is possible to suppress the axial twist phenomenon caused by the speed of each of the generator and the blade. In addition, due to the reduction of the active power output to the system when the power supply low voltage occurs, overvoltage occurs on the DC link side to prevent the destruction of the power conversion converter.

1 is a view showing an example of a PMSG type variable speed wind power generation system to which the present invention is applied;
2 is a view showing an example of the modeling of the wind turbine drive train of the wind power generation system to which the present invention is applied,
FIG. 3 is a diagram illustrating a board plot of a transfer function of the wind turbine drive train of FIG. 2. FIG.
4 is a diagram illustrating an example of a DBR control block for controlling when a system accident occurs according to the present invention;
5 is a view showing an example of a block diagram for the control of the generator-side converter (MSC) in the event of a system accident according to the present invention,
6 is a view showing a simulation result of the pulsed torque reduction method according to the present invention;
7 is a view showing an example of a control method of a generator-side converter (MSC) when a system accident occurs in accordance with the present invention, and
8 is a diagram illustrating an example of a control method when a system accident occurs according to the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail the control device and method of the wind power generation system according to the present invention.

1 is a view showing an example of a PMSG type variable speed wind power generation system to which the present invention is applied.

Referring to FIG. 1, the mechanical torque input by the pitch control of the blade 100 is converted into electrical energy through the PMSG 110 and the machine side converter (MSC) 120, and the converted electrical energy is The grid is supplied to the grid through a grid side converter (GSC) 140. In this case, the generator-side converter (MSC) 120 controls the speed of the rotor in order to produce an optimum output, and the grid-side converter (GSC) 140 performs frequency conversion and power factor control.

2 is a view showing an example of the modeling of the wind turbine drive train of the wind power generation system to which the present invention is applied.

1 and 2 together, the wind turbine drive train is composed of a rotor system (J _r ) and generator inertia (J _g ), a complex system of gearboxes and shaft drives. Reducing this complex system can be typically represented by 2-mass modeling of rotor inertia (J _r ) 200 and generator inertia (J _g ) 210. At this time, the difference between the rotor speed (ω _r ) and the generator speed (ω _g ) occurs due to the shaft torsion, and the torsion of the shaft is as if the rotor and the generator are connected by the spring (K _sh ). Because of this, the torque equation in 2-mass modeling is divided into rotor torque (T _r ), generator torque (T _g ), and axial torque (T _sh ). When 2-mass modeling is expressed as an equation, it is expressed as the following equation.

Using this transfer function, when a board plot is plotted as shown in FIG. 3, the resonant frequency component of the drive train (ω ₀ ) appears.

In the full-power converter method, overvoltage may occur on the DC-Link (V _dc ) side due to the reduction of the effective power output to the system when a low voltage of the power supply occurs, which may cause the power converter to be destroyed.

The power generated by the wind turbine fills the DC-Link voltage through the generator-side converter (MSC) 120 and the grid-side converter (GSC) 140 maintains the DC-Link voltage constant. This outputs the same amount of power to the grid. Therefore, the DC link voltage is determined by the difference between the power of the generator-side converter (MSC) 120 and the power of the grid-side converter (GSC) 140.

In the event of a grid accident, the power output to the grid side suddenly disappears or decreases, causing surplus power and increasing the DC voltage, which can damage the system due to overvoltage.

In order to reduce the rise of DC-Link voltage in the event of a system accident, the method consumes extra power in the Dynamic Braking Resistor (DBR) 130 and reduces the load torque in the generator-side converter (MSC) 120 to generate power. You can use a method to reduce power.

However, as the grid code of each country is gradually strengthened in recent years, the duration of Low Voltage Ride Through (LVRT) increases and the voltage decrease tends to increase. Follows. Therefore, in the worst condition, DC link voltage (V _dc ) increase due to low voltage is calculated and accumulated energy is calculated to select DC-Link capacitor and DBR capacity, and generator in case of low voltage (LV, Low Voltage) accident Through control, it is necessary to reduce the input power and take secondary means such as pitch control.

Torque (T _r ) input from the rotor blade is determined by the characteristics of the blade, such as wind speed and output coefficient can be expressed as shown in Equation 2 below. In this case, it is assumed that the wind speed is constant so that there is no pulsation of the blade torque, but in reality, there are pulsating torques of various frequencies due to irregular fluctuations of the wind speed and complicated aerodynamic characteristics such as tower effect and shear effect. If there is a component corresponding to the natural vibration frequency among the frequency components of the torque ripple, the torsional vibration of the system can be continued.

In the generator-side converter (MSC) 120, there are speed control and torque control as a method of controlling a generator. In general, a wind power generation system having a large inertia has a slow speed variation, so that the ripple in the output power is reduced when torque control is used. There is this. That is, below the rated wind speed, it is necessary to increase the generator load torque in proportion to the square of the rotation speed as shown in Equation 3 in order to increase the rotational speed in order to maintain the optimum speed ratio of the blade. In this way, if the generator torque is controlled to an appropriate value, it converges to the rotational speed capable of maintaining the maximum output coefficient at the current wind speed, so that maximum power point tracking (MPPT) can be performed.

When the generator power is reduced in the generator-side converter (MSC) 120, the load torque, which is in balance with the blade torque, is rapidly decelerated, thereby increasing the speed of the rotor. At this time, when analyzing the dynamic characteristics of the wind turbine drive train of the 2-mass modeling of Figure 2 it can be seen that a sudden torque change occurs the rotor speed and the generator speed difference and the torsional vibration of the shaft occurs. If the load torque in the generator-side converter (MSC) 120 is reduced in steps, axial torsional vibration occurs due to the natural vibration frequency component. In order to suppress such torsional vibration phenomenon, a control strategy that removes the resonance frequency components included in the blade torque and the generator load torque or suppresses the vibration is required.

4 is a diagram illustrating an example of a DBR control block when a system accident occurs according to the present invention.

Referring to FIG. 4, the DBR controller includes a first comparator 400, a proportional integral ratio divider 410, a limiter 420, and a second comparator 430.

The first comparator 400 outputs a difference between the preset DC link voltage threshold value V _{dc _ limit} and the DC link voltage. The proportional integral derivative 410 compensates the error value output by the first comparator 400 so that the threshold value can be quickly reached. The limiter 420 limits the output of the proportional integral derivative 410 within a predetermined range. For example, the limiter 420 limits the output of the proportional integral derivative 410 to a value between zero and one. The second comparator 430 compares the output of the limiter 420 and the carrier wave 440 and outputs the DBR trigger signal 450. Here, the carrier 440 has a frequency higher than the resonant frequency of the drive train of the wind turbine. That is, the frequency of the carrier 440 is higher than the resonance frequency of the 2-mass modeling. The frequency of the carrier 440 may be 10 times higher than the resonant frequency, depending on the application, such that the optimum frequency can be obtained through various experiments. The DBR trigger signal 450 thus obtained is a pulse type signal. In detail, the signal output through the second comparator 430 becomes a signal of a pulse width modulation (PWM) type.

5 is a view showing an example of a block diagram for the control of the generator-side converter (MSC) in the event of a system accident according to the present invention.

Referring to FIG. 5, the generator portion 500 of the wind power generation system may be divided into a portion 510 for modeling a blade and a portion 520 for modeling a drive train of a wind turbine. The blade can be modeled by various conventional methods, and the blade modeling method itself is beyond the scope of the present invention, and thus a detailed description thereof will be omitted. In addition, the model 2-520 of the drive train of the wind turbine has been described with reference to the 2-mass model in FIG. 2, but this is only presented to help the understanding of the present invention various conventional modeling methods of the drive train of the wind turbine can be applied. have. That is, what the present invention intends to present in FIG. 5 is not a modeling method, but how to control the load torque in the generator-side converter.

Looking specifically below, the control device 550 of the wind power generation system is largely composed of a maximum output control unit 560 and the load torque control unit 570. The maximum output control unit 550 controls the blade torque T _blade and the load torque T _g of the generator to be balanced so that the maximum output can be obtained. Various methods are conventionally proposed as the maximum output control method, and in this embodiment, it is only necessary to grasp the value of the load torque at the maximum output control regardless of which method is used.

The load torque control unit 570 performs a process of reducing the output of the load torque generated by the maximum output control unit 560 by a predetermined ratio according to the salpin DBR trigger signal 450 in FIG. 4. The load torque control unit 570 uses K _LV , a value between 0 and 1, as a gain for reducing the load torque calculated by the maximum output control unit 560.

That is, the load torque control unit 570 outputs a reduced ratio of the load torque calculated by the maximum output control algorithm when the DBR trigger signal in the pulse form is on, and calculates the maximum output control algorithm when the DBR trigger signal is off. The torque applied is output as it is and torque control is performed.

Therefore, the power generated by the generator is also reduced by reducing the load torque of the generator. If the power generated by the selected ratio of K _LV decreases, the power consumed by the DBR during LVRT is also reduced. Therefore, the DBR capacity is reduced to reduce the cost or heat loss.

Torque ripple occurs according to the pulse period of the DBR trigger signal, but this ripple frequency is far from the resonance frequency of the axis with high inertia, so it has little effect on resonance. If the generator side torque is reduced in the form of PWM, the speed will eventually increase, but the speed increase will be reduced compared to the case where the load is reduced by the constant torque reduction method. This effect can be confirmed through FIG.

6 is a view showing a simulation result of the PWM torque reduction method according to the present invention.

Referring to FIG. 6, it is assumed that the wind speed is constant at 11 [rad / sec], which is the rated wind speed in this simulation. As shown in Fig. (A), when a 15% low voltage occurs at 500 [ms] for 10 seconds, the DC-Link voltage increases (b) and the DC-Link voltage is 1400V. DBR trigger that has been increased abnormally is turned on / off (c). In the case of Fig. (E), when the K _LV constant shown in FIG. 5 is set to 0.5, the load torque is reduced by 50% in the generator-side converter (MSC) according to the DBR trigger signal. As shown in Fig. (D), the generator and rotor speed increase about 0.5 [rpm] from the rated load due to the decrease of load torque, but the speed of generator and rotor converges to the rated speed when the grid voltage returns to normal after 10.5 seconds. In Figure (f), the shaft torque also vibrates due to the reduction of the generator's load torque, but converges to zero after 10.5 seconds.

7 is a diagram illustrating an example of a method of controlling a generator-side converter (MSC) when a system accident occurs according to the present invention.

Referring to FIG. 7, the controller obtains a difference between a preset threshold value of the DC link voltage and the current DC link voltage (S700), and compensates the voltage difference by using proportional integral control (S710). Using the limiter, the difference is limited to a value between 0 and 1 (S720). The controller generates a pulse-shaped DBR trigger signal by obtaining a difference between a signal having a frequency greater than the resonance frequency of the wind turbine drive train and a signal passing through the limiter (S730). If the DBR trigger signal is on (S740), the output torque is reduced by a certain ratio and outputted by the maximum output control algorithm (S750). The load torque is output as it is (S760).

8 is a diagram illustrating an example of a control method when a system accident occurs according to the present invention.

Referring to FIG. 8, since the DC link voltage rises during a system accident, the control device determines whether the feedback DC link voltage reaches a predetermined threshold value (S800 and S810). When the DC link voltage reaches the threshold value, the controller checks the magnitude of the grid voltage to determine whether the grid voltage is greater than or equal to the preset division value (S820). For example, in case of a system accident, the division voltage can be determined by setting the division value to 50% or more and 50% or less.

When the magnitude of the grid voltage decreases by more than the divided value, the controller performs DBR control in the grid-side converter (GSC) and torque control in the generator-side converter (MSC) at the same time (S830). If it decreases below, only the torque control is performed in the generator-side converter (MSC) to perform LVRT control (S840).

For example, by dividing the above division value into more than 50% and below, when the system accident occurs, the share ratio is equal in DBR control and generator side torque control to consume 50% of surplus power that is not output to the system side. In the case of a minor system accident, the LVRT is controlled only by the generator side torque control, thereby reducing losses such as switch loss and heat loss that occur when operating the DBR. In other words, it is possible to adjust the sharing ratio between the DBR control and the torque control of the generator, so that the LVRT control can be effectively performed by reducing the loss in the DBR.

The present invention can also be embodied as computer-readable codes on a computer-readable recording medium. A computer-readable recording medium includes all kinds of recording apparatuses in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disks, optical data storage devices, and the like. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

So far I looked at the center of the preferred embodiment for the present invention. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (9)

A DBR controller configured to generate a pulse-shaped DBR trigger signal having a frequency greater than a resonance frequency of the wind turbine drive train based on a difference between a preset threshold value and a DC link voltage; And
And a load torque control unit for performing an operation of reducing and outputting a predetermined ratio with respect to the load torque during maximum output control in accordance with the DBR trigger signal. The method of claim 1, wherein the DBR control unit,
A first comparison unit outputting a difference between the preset threshold value and the DC link voltage;
A proportional integral derivative to compensate the output value of the first comparator;
A limiter for limiting the output of the proportional integral derivative to a value in a predetermined range; And
And a second comparator for outputting the difference between the carrier having a frequency greater than the resonance frequency of the wind turbine drive train and the output value of the limiter as the DBR trigger signal. The method of claim 1, wherein the load torque control unit,
Outputting the first output when the DBR trigger signal is off and outputting the second output when the first output of the load torque for the maximum output control and the second output of which the magnitude of the first output is reduced by a certain ratio. Control device for wind power generation system characterized in that. Generating a pulse-shaped DBR trigger signal having a frequency greater than a resonant frequency of the wind turbine drive train based on a difference between the preset threshold value and the DC link voltage; And
And reducing the magnitude of the load torque during maximum output control in accordance with the DBR trigger signal and outputting the predetermined ratio. The method of claim 4, wherein generating the DBR trigger signal comprises:
Obtaining a difference value between the preset threshold value and the DC link voltage;
Compensating for the difference using proportional integral derivative control;
Limiting the output value of the compensating step to a range of values using a limiter; And
And outputting, as the DBR trigger signal, a difference between a carrier having a frequency greater than a resonance frequency of the wind turbine drive train and the limited output value as the DBR trigger signal. The method of claim 4, wherein the outputting step,
Outputting a value of decreasing the magnitude of the load torque by a predetermined ratio when the DBR trigger signal is on; And
If the DBR trigger signal is off, outputting as it is without reducing the magnitude of the load torque; control method of a wind power generation system comprising a. delete Determining whether the DC link voltage reaches a preset threshold value;
When the DC link voltage reaches the threshold, determining whether a magnitude of a system voltage exceeds a predetermined division value;
When the magnitude of the grid voltage exceeds the division value, the DBR control according to the DBR trigger signal and the torque control of the generator-side converter are simultaneously performed, and when the magnitude of the grid voltage does not exceed the preset division value, the generator side Performing only torque control of the converter;
The DBR control generates a pulse-shaped DBR trigger signal having a frequency greater than the resonance frequency of the wind turbine drive train based on a difference between a predetermined threshold value and a DC link voltage, and controls the maximum output according to the DBR trigger signal. The control method of the wind power generation system, characterized in that the control to output a reduced proportion of the magnitude of the load torque. A computer-readable recording medium having recorded thereon a program for performing the method according to any one of claims 4 to 6 and 8.

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