CN110460053B - Grid-connected filtering automatic adjusting system and method for double-fed wind turbine generator - Google Patents

Grid-connected filtering automatic adjusting system and method for double-fed wind turbine generator Download PDF

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CN110460053B
CN110460053B CN201910339340.XA CN201910339340A CN110460053B CN 110460053 B CN110460053 B CN 110460053B CN 201910339340 A CN201910339340 A CN 201910339340A CN 110460053 B CN110460053 B CN 110460053B
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filter
frequency
grid
motor
current
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CN110460053A (en
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陈琳
冀俊茹
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Nanjing Polytechnic Institute
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention discloses a grid-connected filtering automatic regulating system of a double-fed wind turbine generator, which is characterized in that an LC branch circuit is connected in parallel with a filter capacitor of an original LCL filter, and the LC branch circuit comprises an inductor L in series connection Z A capacitor C Z One switching switch Q Z Said Q Z The switching of the LC branch circuit is controlled by a processor, and when the harmonic frequency of the motor teeth under the current rotating speed of the processor is close to the resonance frequency of the filter, the switching of the added LC branch circuit is controlled Z And changing the current switching state. The invention also provides an automatic adjustment method, the tooth harmonic frequency of the motor at the current rotating speed is calculated through the measurement of the rotating speed of the generator, and when the tooth harmonic frequency is close to the resonant frequency of the current filter, the switching of the added LC branch circuit is controlled, the resonant frequency of the filter is changed, and the automatic adjustment is realized. The invention can solve the problems of overlarge harmonic current and resonance caused by coupling of the tooth harmonic wave of the double-fed wind turbine generator and the LCL filter, and improve the integral reliability and the grid-connected electric energy quality of the generator.

Description

Grid-connected filtering automatic adjusting system and method for double-fed wind turbine generator
Technical Field
The invention relates to the technical field of wind power generation, in particular to a system and a method for automatically adjusting grid-connected filtering of a double-fed wind turbine generator.
Background
With the rapid development of power electronic technology, wind power generation equipment is connected to the grid by adopting a power electronic converter in a large quantity. Since power electronic equipment works in a switching mode, a filter needs to be configured at an output end of the power electronic equipment, and an LCL filter is widely applied at present. The LCL filter belongs to a third-order filter, has stronger harmonic attenuation capability in a high frequency band, but simultaneously presents extremely low impedance at the inherent resonance frequency, and when a harmonic source exists in the frequency band, the phenomenon of overlarge harmonic current is easy to occur, and even the resonance problem is caused. For the double-fed wind turbine generator, because of the tooth space effect of the double-fed motor, tooth harmonic voltage exists, when the tooth harmonic frequency is close to the resonant frequency of the LCL filter circuit, large harmonic current can be generated, and tooth harmonic resonance occurs, so that on one hand, the harmonic loss of the motor is increased, and on the other hand, the resonance risk is formed on a grid-connected system. The tooth harmonic frequency of the doubly-fed motor changes along with the rotating speed, the frequency range generally covers the range of 700-1500 Hz, the resonant frequency of the LCL filter circuit is required to be kept in the frequency range (the resonant frequency is higher than the frequency band and cannot achieve the corresponding filtering effect, and larger capacitance and inductance are required to be configured below the frequency band, so that the equipment cost is high, and static reactive power exceeds the design index), and coupling is difficult to avoid in design. To cope with this problem, a filter circuit is generally used to increase resistance and improve damping. However, increasing the resistance will on the one hand reduce the filtering performance and on the other hand increase the system loss. Therefore, a method for suppressing the tooth harmonic resonance of the doubly-fed wind turbine needs to be found.
Disclosure of Invention
1. The technical problem to be solved is as follows:
the existing double-fed motor has tooth harmonic voltage due to the tooth space effect, and when the tooth harmonic frequency is close to the resonant frequency of the LCL filter circuit, large harmonic current can be generated, tooth harmonic resonance occurs, so that on one hand, the harmonic loss of the motor is increased, and on the other hand, the resonant risk is formed on a grid-connected system. The existing solution is to increase the resistance of the filter loop to improve the damping, but increasing the resistance will reduce the filter performance on one hand and increase the system loss on the other hand.
2. The technical scheme is as follows:
in order to solve the problems, the invention provides an automatic grid-connected filtering adjusting system of a double-fed wind turbine generator, which comprises a processor, wherein an LC branch circuit is connected in parallel with a filter capacitor of an original LCL filter, and the LC branch circuit comprises an inductor L in series connection Z A capacitor C Z One switching switch Q Z Inductance L Z The left end of the transformer is connected with a double-fed wind power converter and an inductor L Z Is connected with the power grid, Q Z The switching of the filter is controlled by a processor, and when the harmonic frequency of the motor teeth under the current rotating speed of the processor is close to the resonance frequency of the filter, the switching of the filter is controlledSwitching switch Q for producing added LC branch Z And changing the current switching state.
The inductance L Z The function of (2) is to limit the inrush current at the moment of capacitor application.
A storage device is also included for storing instructions that are adapted to be loaded and executed by the processor.
The invention also provides an automatic adjusting method of the double-fed wind turbine generator grid-connected filtering automatic adjusting system, which comprises the following steps: step S01: measuring and measuring the rotating speed of the doubly-fed generator, calculating the current slip ratio s, and obtaining the tooth harmonic central frequency f through a formula alh0 And step S02: judge the fling-cut switch Q Z Calculating the resonant frequency f of the filter loop res (ii) a Step S03: when | f alh0 -f res |<150Hz, the processor sends out a control instruction to change the switching switch Q Z Switching state of the switch; step S04, switching switch Q Z The electrical connection of the filter circuit is changed according to the command operation, so that the resonant frequency of the circuit is far away from the tooth harmonic frequency.
Tooth harmonic center frequency f alh0 The calculation formula of (2) is as follows:
Figure BDA0002040222140000021
wherein S represents the number of rotor slots of the motor, N P The number of poles of the motor is shown, and s represents the slip of the motor.
The number of the tooth grooves of the rotor is 60 grooves or 48 grooves.
The slip ratio of the motor
Figure BDA0002040222140000022
Wherein n is 1 And n is the current running speed of the motor.
The number of poles NP of the motor is 4.
In step S02, Q Z At the time of disconnection
Figure BDA0002040222140000023
Q Z When put into
Figure BDA0002040222140000024
Wherein L is 1 Side inductance value of current transformer, L 2 To grid side inductance value, C f Is the filter capacitance value.
3. Has the advantages that:
the invention solves the problems of overlarge harmonic current and resonance caused by the coupling of the tooth harmonic wave of the double-fed wind turbine generator and the LCL filter, and improves the integral reliability and grid-connected electric energy quality of the generator. Compared with the prior art, the energy consumption resistive element is not used, so that active loss and reduction of power generation efficiency caused by damping resistance are avoided; the resonance frequency of the circuit is changed, the frequency coupling of the tooth harmonic and the filter circuit is avoided fundamentally, and the reliability is higher.
Drawings
Fig. 1 is a schematic diagram of an LCL filter topology employing the present invention.
Fig. 2 is a control block diagram of the present invention.
Fig. 3 is a bode diagram of the LCL filter of the present invention.
FIG. 4 is a graph of the relationship between the operating speed of the doubly-fed wind turbine generator and the tooth harmonic frequency.
Detailed Description
The invention is explained in detail below with reference to the figures and examples.
As shown in FIG. 1, the invention provides an automatic grid-connected filtering adjusting system for a doubly-fed wind turbine generator, which comprises a processor, wherein an LC branch circuit is connected in parallel with a filter capacitor of an original LCL filter, and the LC branch circuit comprises an inductor L in series connection Z A capacitor C Z One switching switch Q Z Inductance L Z The left end of the transformer is connected with a double-fed wind power converter and an inductor L Z The right end of the switch is connected with a power grid, and the switch Q can be used as a branch z At turn-off, the filter transfer function is
Figure BDA0002040222140000031
Wherein L is 1 Side inductance value of current transformer, L 2 To grid side inductance value, C f For filter capacitance values, a bode plot of the transfer function is plotted, as shown in fig. 4As shown by the line, as can be seen from the amplitude-frequency characteristic curve of FIG. 3, the system has a resonance peak with a resonance frequency of
Figure BDA0002040222140000032
When the switch Q of the branch can be switched z When closed, the filter transfer function becomes
Figure BDA0002040222140000033
As shown by the dotted line in fig. 4, it can be seen from the amplitude-frequency characteristic curve that the resonance peak is significantly shifted to the low frequency band. In the LC switchable branch, the inductance L Z The main function of (2) is to limit the inrush current at the moment the capacitor is switched on, so that a smaller inductance value can be chosen. Approximate calculation of resonant frequency of
Figure BDA0002040222140000034
As shown in fig. 2, in the method for automatically adjusting grid-connected filtering of a doubly-fed wind turbine generator, the tooth harmonic frequency of a motor at the current rotating speed is calculated through the measurement of the rotating speed of a generator, then frequency coupling degree comparison is carried out, and when the tooth harmonic frequency is close to the resonant frequency of a current filter, the switching switch Q of an added LC branch is controlled Z And changing the current switching state.
Examples
The calculation formula of the harmonic frequency of the doubly-fed motor teeth is as follows
Figure BDA0002040222140000035
Wherein f is 1 The grid voltage frequency after grid connection is represented, S represents the number of rotor slots of the motor, N P The number of poles of the motor is indicated, and s indicates the slip of the motor. The number of tooth slots commonly used for designing the doubly-fed wind generator is 60 slots or 48 slots, the number of poles is commonly 4 poles, and the slip ratio of the motor
Figure BDA0002040222140000036
Wherein n is 1 For synchronous speed, n is the current running speed of the motorAnd for a 4-pole motor running in a 50Hz power grid, the synchronous rotating speed is 1500 rpm, and the normal running slip ratio range of the double-fed wind turbine generator is generally-0.3-0.2. Taking a 48-slot motor as an example, the relation between the operating rotating speed and the tooth harmonic frequency of the doubly-fed wind turbine generator is shown in fig. 4.
The implementation steps of the invention are as follows:
1) Measuring the rotating speed of the doubly-fed generator, calculating the current slip ratio s, and calculating the current slip ratio s according to a calculation formula
Figure BDA0002040222140000041
Obtaining the tooth harmonic central frequency f alh0 ；
2) Judge the fling-cut switch Q z Calculating the resonant frequency f of the filter loop res If Q is z Disconnect
Figure BDA0002040222140000042
If Q z Is thrown in
Figure BDA0002040222140000043
3) When f alh0 -f res |<150Hz, sending out a control instruction and changing a switching switch Q Z The switching state of (2).
4) Control fling-cut switch Q z The electrical connection of the filter circuit is changed according to the command operation, and the circuit resonance frequency is separated from the tooth harmonic frequency.
Said Q Z The switching of the LC branch circuit is controlled by a processor, and when the harmonic frequency of the motor teeth under the current rotating speed of the processor is close to the resonance frequency of the filter, the switching switch Q of the added LC branch circuit is controlled Z And changing the current switching state.
Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (9)

1. The utility model provides a double-fed wind turbine generator system filtering automatic regulating system that is incorporated into power networks, includes the treater, its characterized in that: an LC branch circuit is connected in parallel with a filter capacitor of the LCL filter and comprises an inductor L in series connection Z A capacitor C Z One switching switch Q Z Inductance L Z The left end of the transformer is connected with a double-fed wind power converter and an inductor L Z Is connected with the power grid, Q Z The switching of the LC branch circuit is controlled by a processor, and when the harmonic frequency of the motor teeth under the current rotating speed of the processor is close to the resonance frequency of the filter, the switching switch Q of the added LC branch circuit is controlled Z And changing the current switching state.
2. The doubly-fed wind turbine grid-connected filtering automatic regulating system of claim 1, characterized in that: the inductor L Z The function of (1) is to limit the inrush current at the moment the capacitor is switched on.
3. The grid-connected filtering automatic adjusting system of the doubly-fed wind turbine generator set according to claim 1 or 2, characterized in that: a storage device is also included for storing instructions that are adapted to be loaded and executed by the processor.
4. An automatic adjusting method applied to the double-fed wind turbine grid-connected filtering automatic adjusting system of any claim 1 to 3, comprising the following steps: step S01: measuring the rotating speed of the doubly-fed generator, calculating the current slip ratio s, and obtaining the tooth harmonic central frequency f through a formula alh0 And step S02: judge the fling-cut switch Q Z Calculating the resonant frequency f of the filter loop res (ii) a Step S03: when | f alh0 -f res |<150Hz, the processor sends out a control instruction to change the switching switch Q z Switching state of the switch; and S04, the fling-cut switch QZ acts according to the instruction to change the electrical connection of the filter circuit so as to lead the resonant frequency of the circuit to be far away from the tooth harmonic frequency.
5. The automatic adjustment method of claim 4, characterized in that: tooth harmonic center frequency f alh0 The calculation formula of (c) is:
Figure FDA0003969980250000011
wherein S represents the number of rotor slots of the motor, N P Representing the number of poles of the motor, s representing the motor slip, f 1 And the grid voltage frequency after grid connection is represented.
6. The automatic adjustment method of claim 5, characterized in that: the number of the tooth grooves of the rotor is 60 grooves or 48 grooves.
7. The automatic adjustment method of claim 5, characterized in that: the slip ratio of the motor
Figure FDA0003969980250000012
Wherein n is 1 And n is the current running speed of the motor.
8. The automatic adjustment method of claim 5, characterized in that: the number of poles N of the motor P Is 4 poles.
9. The automatic adjustment method according to any one of claims 4-6, characterized in that: in step S02, Q Z At the time of disconnection
Figure FDA0003969980250000013
Q Z When put into
Figure FDA0003969980250000014
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