CN110148965B - An Adaptive Method for Sampling Transformers at Grid-connected Control Points of Active Converters - Google Patents

Abstract

The invention discloses an adaptive method for sampling a transformer at a grid-connected control point of an active converter. The adaptive method includes the following steps: a. After performing CT sampling on a load with a non-linear load, the current After FFT analysis, extract the harmonic components, and at the same time select a harmonic order that does not appear or the current is much larger than the harmonic order of the extracted harmonic; b. Let the converter send out this harmonic pulse, according to the predetermined result should be : When the output current sampling transformer CT1 of the converter and the grid current sampling transformer CT2 can detect the harmonic current value sent by the converter at the same time, the grid current sampling transformer CT2 obtains a value that is not multiplied by the transformation ratio after sampling value, it is judged that the grid current sampling transformer CT2 is located on the grid side.

Description

An Adaptive Method for Sampling Transformers at Grid-connected Control Points of Active Converters

technical field

The invention relates to the technical field of grid-connected control of active converters, in particular to an adaptive method for sampling transformers at grid-connected control points of active converters.

Background technique

With the development of power electronics technology and the increasing processing capacity of microprocessors, computer real-time control technology and various advanced algorithms are continuously used in power electronic converter devices. Since the power electronic converter is used in the power system, in order to stabilize the grid connection, it is necessary to sample the voltage and current signals to form a closed-loop feedback control;

The active converter is composed of grid current sampling transformer CT2, converter output current sampling transformer CT1, converter and controller. In the past, the location and transformation ratio of CT2 should be set and confirmed manually, which is limited by human factors and level factors, which is time-consuming and labor-intensive.

In the existing technology, there is no specific technical description for the positioning of the sampling position, the online self-inspection technology and the judgment method.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides an adaptive method for the sampling transformer of the grid-connected control point of the active converter, aiming to solve the problem of manual identification of the installation position and transformation ratio of the grid current sampling transformer CT2 in the past .

In order to achieve the above object, the present invention provides the following technical solution: an adaptive method for the sampling transformer of the grid-connected control point of the active converter, the active converter is output by the grid current sampling transformer CT2 and the converter A current sampling transformer CT1, a converter and a controller are formed; the adaptive method includes the following steps:

a. After CT sampling is performed on the load with nonlinear load, after FFT analysis of its current, the harmonic component is extracted, and at the same time, a certain harmonic order that does not appear or a harmonic order whose current is much larger than the extracted harmonic is selected;

b. Let the converter send out this harmonic pulse, according to the predetermined result:

(1) When the output current sampling transformer CT1 of the converter and the grid current sampling transformer CT2 can detect the current harmonic current value sent by the converter at the same time, the grid current sampling transformer CT2 samples and obtains a value that is not multiplied by the transformer ratio value, it is judged that the grid current sampling transformer CT2 is located on the grid side;

(2) When the effective value current corresponding to the harmonic pulse that can be resolved in the output current sampling transformer CT1 of the converter, and there is current in the grid current sampling transformer CT2, but there is no current effective value, it can be determined that the grid current sampling Transformer CT2 is not connected to the grid side and is located on the load side.

Further, in the step b, when it is determined that the grid current sampling transformer CT2 is located on the grid side, the value in the output current sampling transformer CT1 is converted into an effective value A1, and the sub-harmonic is converted into an effective value B1 to obtain Output transformation ratio = B1/A1, stored in the adopted calculation channel.

Preferably, in the step a, a certain harmonic order that does not appear is selected.

Preferably, the selected current in step a is the harmonic order 100 times the extracted harmonic.

Beneficial effects of the present invention: the positioning technology of CT, the automatic recognition technology of variable ratio, effectively avoid the open-loop control and positive feedback; at the same time, the effective identification and detection of the control system to its sensor system are improved, and the whole life cycle can be realized. Monitor the state of the CT; when the CT is installed, in order to confirm whether the installation position of the CT is accurate and whether the transformation ratio is set correctly; the device can be re-started for sampling and testing after a long time idle.

Description of drawings

Fig. 1 is a structural block diagram of the grid-connected control system of the active converter of the present invention.

Detailed ways

As shown in Figure 1, an adaptive method for the grid-connected control point sampling transformer of an active converter, the active converter consists of grid current sampling transformer CT2, converter output current sampling transformer CT1, The converter and the controller are composed; the adaptive method includes the following steps: first, regardless of whether the current sampling transformer CT2 is located on the grid side or the load side at this time, for the entire converter device, when no current is sent, the grid The waveforms detected by the current sampling transformer CT2 on the side or the load side are consistent. After CT sampling is performed on the load with a nonlinear load, its current is analyzed. Since there may be many types, after FFT analysis, the harmonics are extracted. component, and at the same time select a harmonic order that does not appear; then let the converter send out this harmonic pulse, according to the predetermined result:

(1) When the output current sampling transformer CT1 of the converter and the grid current sampling transformer CT2 can detect the current harmonic current value sent by the converter at the same time, the grid current sampling transformer CT2 samples and obtains a value that is not multiplied by the transformer ratio value, it is judged that the grid current sampling transformer CT2 is located on the grid side; the value in the output current sampling transformer CT1 is converted into an effective value A1, and the harmonic is converted into an effective value B1, and the transformation ratio = B1/ A1, stored in the adoption calculation channel.

(2) When the effective value current corresponding to the harmonic pulse that can be resolved in the output current sampling transformer CT1 of the converter, and there is current in the grid current sampling transformer CT2, but there is no current effective value, it can be determined that the grid current sampling Transformer CT2 is not connected to the grid side and is located on the load side.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement or improvement made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (4)

1. The active converter consists of a power grid current sampling transformer CT2, a converter output current sampling transformer CT1, a converter and a controller; the self-adaptive method is characterized by comprising the following steps of:

a. after CT sampling is carried out on a load with nonlinear load, after FFT analysis is carried out on current of the load, harmonic components are extracted, and harmonic times which do not appear at a certain time or harmonic times which are far larger than the extracted harmonic are selected at the same time;

b. letting the converter emit this harmonic pulse according to a predetermined result:

(1) When the current transformer output current sampling transformer CT1 and the power grid current sampling transformer CT2 can detect the harmonic current value emitted by the current transformer at the same time, the power grid current sampling transformer CT2 obtains a value which is not multiplied by a transformation ratio after sampling, and the power grid current sampling transformer CT2 is judged to be positioned at the power grid side;

(2) When the current transformer outputs the effective value current corresponding to the harmonic pulse which can be analyzed and sent out in the current sampling transformer CT1, the current exists in the power grid current sampling transformer CT2, but no effective value exists at the time, the condition that the power grid current sampling transformer CT2 is not connected to the grid side and is positioned on the load side can be judged.

2. The adaptive method of an active converter grid-connected control point sampling transformer according to claim 1, wherein in the step B, when it is determined that the grid current sampling transformer CT2 is located at the grid side, the value in the output current sampling transformer CT1 is converted into an effective value A1, the subharmonic is converted into an effective value B1, and a transformation ratio=b1/A1 is obtained and stored in the calculation channel.

3. The adaptive method of an active converter grid-connected control point sampling transformer according to claim 1, wherein the number of harmonics which do not appear at a time is selected in the step a.

4. The adaptive method of the sampling transformer for the grid-connected control point of the active converter according to claim 1, wherein the current is selected in the step a to be 100 times of the extracted harmonic.

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