CN104701847A - Parameter calculating method for induction filtering branch circuit of wind power plant access system - Google Patents

Abstract

The invention discloses a method for calculating the parameters of the induction filter branch based on the wind farm access system. The single-tuned filter in the LC filter is connected with the filter winding of the transformer to filter out the harmonics generated by the wind farm and compensate the corresponding harmonics. of reactive power. According to the invention, a plurality of single-tuned filters are connected in parallel to the filter winding of the transformer, and different single-tuned filters are used to filter out harmonics of different orders. The method for calculating the parameters of the induction filter branch of the wind farm access system of the present invention can accurately calculate the parameter value of the single-tuned filter, realize effective shielding and reactive power compensation for the main sub-harmonic of wind power, and reduce the impact of wind power grid connection on the access grid Impact.

Description

Calculation method of induction filter branch parameters for wind farm access system

technical field

The invention relates to the field of induction filtering of a wind farm access system, in particular to a method for calculating parameters of a branch based on the induction filtering of a wind farm access system.

Background technique

my country's wind energy construction has entered a period of rapid development. The capacity of wind farms is getting larger and larger, and its impact on the system is becoming more and more obvious. The problem of harmonic pollution is a power quality issue that the power system pays more attention to;

The single-tuned filter in the power system is widely used due to its advantages of small loss, good single harmonic filtering effect, and small short-circuit current, and the parameters of the filter have an important impact on the filtering effect. Therefore, it is necessary to study a parameter Calculation method to make the filter achieve the best filtering effect.

Contents of the invention

In order to solve the above technical problems, the main purpose of this utility model is to provide a method for calculating the parameters of the induction filter branch of the wind farm access system; by deriving the filter impedance and transformer impedance, a scientific basis for the wind farm access Calculation method of system induction filter branch parameters;

In order to achieve the above object, the technical solution of the utility model is achieved in that:

The induction filter branch of the wind farm access system is mainly composed of a single-tuned filter. In the single-tuned filter, it is mainly composed of a capacitor C and an inductor L in series. One end is connected to the induction filter winding of the transformer, and the other end is grounded;

The parameters of the induction filter branch of the wind farm access system need to find the capacitance C and inductance L in the single-tuned filter, and also consider the influence of the impedance of the transformer on the filtering effect to calculate its equivalent inductance , subtracting the influence of the inductance on the filter, the calculated value of the best filter effect parameters can be obtained.

Beneficial effect

The method for calculating the parameters of the induction filter branch of the wind farm access system proposed by this utility model can reduce the impact on the filter effect caused by the transformer impedance, thereby achieving the best filter effect, and realizing effective shielding of main harmonics and no interference. The function of power compensation can greatly reduce the impact of wind power grid connection on grid access.

Description of drawings

Fig. 1 is the schematic diagram of circuit structure of the present invention;

Figure 2 is an equivalent circuit without considering the influence of the transformer;

Figure 3 is an equivalent circuit considering the influence of the transformer;

Description of labels: 1. Wind farm, 2. Grid-connected transformer, 3. Inductive filter tuning branch, 4. AC power grid, A. Simulated wind farm harmonic current source, B. Transformer harmonic source side to filter side, etc. Value reactance, C, system equivalent impedance, , Subharmonic filtering capacitor value in single-tuned filter, , The inductance value in the subharmonic filtering single-tuned filter, , Subharmonic filtering capacitor value in single-tuned filter, , Inductance values in subharmonic filtering single-tuned filters.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing and embodiment:

As shown in Figure 1, it is a schematic diagram of the circuit structure of the invention. In the figure, 1 is the wind farm, connected to the primary winding of the grid-connected transformer 2, 3 is the induction filter tuning branch, connected to the filter branch of the grid-connected transformer, and 4 is the AC power grid;

1. In the induction filter tuning branch, the calculation steps of the parameters are as follows:

1) Select a certain number of harmonics that need to be eliminated, such as the 5th and 7th harmonics;

2) Determine the compensation capacity of the filter branch;

3) Determine the capacitance value C and inductance value L of the filter branch;

Firstly, the capacitance C is calculated according to the assigned reactive power compensation capacity, and the relationship between the single-tuned filter capacitor and the reactor tuned at the nth harmonic frequency is:

Since the system harmonic voltage will be limited to a relatively small value in the end, it can be ignored, that is, it can be considered that the system AC bus voltage only contains fundamental wave components . In this way, in addition to the nth harmonic current flowing through the filter branch, it also flows through the fundamental current for:

Then the fundamental reactive capacity of the filter, namely the compensation capacity, is:

The compensation capacity It is known that, according to the distribution value of reactive power compensation capacity, the parameter value C of the capacitor can be determined as:

In the formula, The reactive power compensation capacity allocated for the n-order filter; n is the resonance order; is the rated line voltage of the system; is the operating angular frequency. Then the inductance can be calculated according to the resonant frequency as:

As shown in Figure 2, it is an equivalent circuit that does not consider the influence of the transformer. The values of the corresponding capacitance C and inductance L are calculated from the above calculation formula. This value is the calculated value when the influence of the internal impedance of the transformer on the filtering effect is not considered;

2. Considering the influence of the transformer impedance, it is necessary to calculate the equivalent inductance of the transformer;

1) Determine the rated capacity of the transformer ;

2) Determine the impedance per unit value of the transformer ;

3) Determine the equivalent inductance of the transformer ;

Since the harmonic current enters the filter circuit through the transformer leakage reactance, affected by the transformer, the resonance conditions of each filter circuit for each harmonic are not in the best filtering state, so the influence of the transformer leakage reactance on the filter should be reduced. The formula for calculating the equivalent reactance of each winding of the transformer is:

Therefore, the inductance value is obtained as:

After considering the influence of impedance in the transformer, its inductance value is converted into a single-tuned filter, so:

In this way, the equivalent circuit considering the influence of the transformer is obtained as shown in Figure 3, and the capacitance and inductance values in the single-tuned filter in this equivalent circuit are the calculated values with the best filtering effect;

The invention realizes the effective shielding and reactive power compensation of the main harmonics of the wind farm by calculating the parameters of the induction filter branch of the wind farm access system, and reduces the influence of the wind power grid connection on the grid access.

Claims (3)

1. A method for calculating the parameters of the induction filter branch of a wind farm access system, characterized in that: Select certain harmonics that need to be eliminated, such as the 5th and 7th harmonics in general; Determine the compensation capacity of the filter branch; Determine the capacitance value C and inductance value of the filter branch ; A method for calculating parameters of an induction filter branch of a wind farm access system, characterized in that: 1) Determine the rated capacity of the transformer ; 2) Determine the impedance per unit value of the transformer ; 3) Determine the equivalent inductance of the transformer ; According to claim 1, a method for calculating the parameters of the inductive filter branch of the wind farm access system is characterized in that, in the single-tuned filter, it is mainly used to filter out the main characteristic harmonics in the harmonic source, generally only It is necessary to set to filter out odd harmonics; among certain harmonics that need to be eliminated, since the filter winding of the transformer connected to the filter is a delta connection, there will be no 3rd harmonic outflow, so n can be set to 5, 7 , 11 times, etc. 2. a kind of wind farm access system induction filter branch parameter calculation method according to claim 1, is characterized in that, at first seek electric capacity C according to the reactive power compensation capacity of distribution, tune in the monotonic tuning of n order harmonic frequency The relationship between filter capacitors and reactors is: Since the system harmonic voltage will be limited to a relatively small value in the end, it can be ignored, that is, it can be considered that the system AC bus voltage only contains fundamental wave components ; In this way, besides the nth harmonic current, the filter branch also flows through fundamental current for: Then the fundamental reactive capacity of the filter, namely the compensation capacity, is: The compensation capacity It is known that, according to the distribution value of reactive power compensation capacity, the parameter value C of the capacitor can be determined as:                       In the formula, The reactive power compensation capacity allocated for the n-order filter; n is the resonance order; is the rated line voltage of the system; is the operating angular frequency. 3. You can find the inductance according to the resonant frequency for: According to claim 2, a method for calculating the parameters of the induction filter branch of the wind farm access system, is characterized in that, since the harmonic current enters the filter circuit through the transformer leakage reactance, and is affected by the transformer, each filter circuit is different for each harmonic The resonance condition of the wave is not the best filtering state, so it is necessary to reduce the influence of the transformer leakage reactance on the filter; the equivalent reactance calculation formula of each winding of the transformer is: Therefore, the inductance value is obtained for: After considering the influence of impedance in the transformer, its inductance value is converted into a single-tuned filter, so: .