A filtering and compensating device for a test transformer

Abstract

The present invention provides a filtering and compensating device for a test transformer, which includes a harmonic detection unit, an instruction current operation unit, a trigger pulse generation unit, and a compensating current generation unit that are electrically connected in sequence; the harmonic detection unit is used to collect the voltage and current signals output by the induction voltage regulator; the instruction current operation unit is used to generate an instruction signal, the trigger pulse generation unit is used to send a pulse drive to the compensating current generation unit; the compensating current generation unit is used to generate a compensating current; the present invention can realize the automatic tracking compensation of the voltage waveform of the induction voltage regulator of the test transformer, effectively limit the high-order harmonics, and make the voltage waveform output by the induction voltage regulator as close to a sine wave as possible. The active filtering and compensation method can also compensate for the capacitive or inductive reactive power during the withstand voltage test, solve the under-compensation or over-compensation phenomenon that occurs when a capacitor or inductor with a fixed capacity is connected in parallel, and improve the capacity utilization rate of the test transformer.

Description

Technical Field

[0001] The present invention relates to the field of electrical test and commissioning, and particularly to a filtering and compensating device for a test transformer. Background Art

[0002] The appearance of harmonic current and harmonic voltage reduces the quality of the sinusoidal waveform of the system voltage, which not only seriously affects the power system itself, but also endangers users and surrounding communication systems. In the past half century, with the popularization and application of power electronic devices, the rapid increase of nonlinear loads (such as the application of electric locomotives, industrial electric furnaces, etc.), especially the application of high-voltage direct current transmission, the problem of harmonic pollution has become increasingly serious, and thus has received widespread attention and emphasis. Technical measures to reduce the impact of harmonics can start from two aspects: one is to start from the harmonic source to reduce the generation of harmonics; the other is to install filtering devices. Common filtering devices include passive filters, active filters, and hybrid filters.

[0003] A passive filter (PF: Passive Filter), also known as an LC filter, is a filtering device composed of a filtering capacitor, a reactor, and a resistor appropriately combined. The industrial application of passive filters has a relatively long history, and its design method is stable and reliable, and the structure is simple. However, its filtering effect depends on the system impedance characteristics and is easily affected by temperature drift, the degree of harmonic pollution on the network, the aging of filtering capacitors, and nonlinear loads. In addition, passive filters can only effectively attenuate specific harmonics, and due to economic and floor area considerations, the number of filters is limited. Therefore, for occasions with rich harmonic content, the filtering effect of passive filters is often not ideal.

[0004] Corresponding to the passive filter is the active filter (APF: Active Power Filter). The active power filter uses the control of the converter to eliminate harmonic current, overcoming the disadvantages of the passive filter. The active power filter has technical advantages that the passive filter cannot match, and thus has received more and more attention.

[0005] Such as Figure 1As shown in the figure: To meet the needs of large-capacity test transformers and achieve the adjustment of test voltage, an induction voltage regulator T1 is used to regulate the voltage of the AC test transformer. The AC power supply is input to the primary coil of the test transformer T2 through the induction voltage regulator T1. Due to the working principle of the induction voltage regulator T1, waveform distortion will inevitably occur, and the main harmonics are the 3rd, 5th, and 7th harmonics, which makes the test voltage waveform significantly distorted, the voltage peak value is very high, there is a risk of breakdown of the test object, and it cannot meet the requirements of the insulation test for the voltage waveform. It is necessary to filter and control the harmonics. At the same time, in order to compensate the reactive power of the test object, a filtering device needs to be set on the low-voltage side of the test transformer T2 to save the capacity of the test transformer; the prior art generally uses a passive filtering device, that is, appropriately composed of capacitors, reactors, and resistors, such as Figure 1 The compensation inductor L is used in

[0006] However, although the passive filtering device has a simple structure, its filtering effect depends on the system impedance characteristics and is easily affected by temperature drift, harmonic pollution degree, filtering capacitor aging, and non-linear load. In addition, the passive filter can only effectively attenuate harmonics of specific frequencies, and for economic reasons, the number of filters is limited. Therefore, for uncertain situations where the harmonic content changes, the filtering effect of the passive filter is often not ideal. In terms of reactive power compensation, under-compensation or over-compensation is likely to occur when using fixed-capacity capacitors or inductors in parallel, resulting in waste of transformer capacity. Summary of the Invention

[0007] The purpose of the present invention is to provide a filtering and compensation device for a test transformer, which is used to solve the problem that the passive filtering device is easily affected by temperature drift, harmonic pollution degree, filtering capacitor aging, and non-linear load, and is also used to solve the problem that under-compensation or over-compensation is likely to occur when using fixed-capacity capacitors or inductors in parallel, resulting in waste of transformer capacity.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] A filtering and compensation device for a test transformer includes a harmonic detection unit, a command current operation unit, a trigger pulse generation unit, and a compensation current generation unit that are electrically connected in sequence;

[0010] The harmonic detection unit includes a voltage transformer, a current transformer, and an A / D converter. The voltage transformer and the current transformer are arranged at the output end of the induction voltage regulator to collect the voltage and current signals output by the induction voltage regulator. The A / D converter is used to convert the analog voltage and current signals into digital voltage and current signals and send the digital voltage and current signals to the command current operation unit;

[0011] The described instruction current operation unit uses a microprocessor, which is used to generate an instruction signal according to the received digital voltage and current signals and send it to the compensation current generation unit;

[0012] The described trigger pulse generation unit uses a trigger pulse generator, which is used to send a pulse drive to the compensation current generation unit according to the instruction signal;

[0013] The described compensation current generation unit is used to generate a compensation current.

[0014] The described harmonic detection unit further includes a sample and hold circuit. The input end of the sample and hold circuit is connected to the output ends of the voltage transformer and the current transformer, and the output end of the sample and hold circuit is connected to the input end of the A / D converter.

[0015] The described harmonic detection unit further includes a filter and amplification preprocessing circuit. The input end of the filter and amplification preprocessing circuit is connected to the output ends of the voltage transformer and the current transformer, and the output end of the filter and amplification preprocessing circuit is connected to the input end of the sample and hold circuit.

[0016] The described microprocessor uses an FPGA.

[0017] The described compensation current generation unit uses a unidirectional parallel type bridge converter.

[0018] Advantages of the present invention:

[0019] The present invention can achieve automatic tracking compensation of the voltage waveform of the test transformer induction regulator, effectively limit high-order harmonics, and make the voltage waveform output by the induction regulator as close to a sine wave as possible; according to the actual situation of the construction site, after the application of this filter compensation device, the risk of breakdown of the device under test during the withstand voltage test can be significantly reduced; at the same time, the active filter compensation method can also compensate for capacitive or inductive reactive power during the withstand voltage test, solve the under-compensation or over-compensation phenomena occurring in the parallel connection of capacitors or inductors with a fixed capacity, improve the capacity utilization rate of the test transformer, and avoid the waste of human and material resources such as construction period delay and rework caused by defects in test equipment. Description of the drawings

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required to be used in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is a structural schematic diagram of an existing test transformer;

[0022] Figure 2 is a schematic structural diagram of the present invention;

[0023] Figure 3 is a schematic structural diagram of the harmonic detection unit of the present invention. Detailed implementation manners

[0024] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0025] As Figure 2 and Figure 3 shown: A filtering and compensating device for a test transformer described in the present invention includes a harmonic detection unit, an instruction current operation unit, a trigger pulse generation unit, and a compensation current generation unit that are electrically connected in sequence; the harmonic detection unit includes a voltage transformer PT, a current transformer CT, and an A / D converter. The voltage transformer PT and the current transformer CT are arranged at the output end of the induction regulator T1 for collecting the voltage and current signals output by the induction regulator T1. The A / D converter is used to convert the analog voltage and current signals into digital voltage and current signals, and send the digital voltage and current signals to the instruction current operation unit; the instruction current operation unit uses a microprocessor, and the microprocessor is used to generate an instruction signal according to the received digital voltage and current signals and send it to the compensation current generation unit; the trigger pulse generation unit uses a trigger pulse generator to send a pulse drive to the compensation current generation unit according to the instruction signal; the compensation current generation unit is used to generate a compensation current.

[0026] Preferably, the harmonic detection unit further includes a sample and hold circuit. The input end of the sample and hold circuit is connected to the output ends of the voltage transformer PT and the current transformer CT, and the output end of the sample and hold circuit is connected to the input end of the A / D converter.

[0027] Preferably, the harmonic detection unit further includes a filtering and amplification preprocessing circuit. The input end of the filtering and amplification preprocessing circuit is connected to the output ends of the voltage transformer PT and the current transformer CT, and the output end of the filtering and amplification preprocessing circuit is connected to the input end of the sample and hold circuit.

[0028] Preferably, the microprocessor uses an FPGA.

[0029] Preferably, the compensation current generation unit uses a single-phase shunt type bridge converter.

[0030] The working principle of the present invention is as follows:

[0031] The voltage transformer PT and current transformer CT collect the analog voltage and current signals output by the induction regulator T1. After being amplified and filtered by the filtering and amplification preprocessing circuit, since a certain conversion time is required for A / D conversion of the analog signal, the sampling and holding circuit can keep the analog voltage and current signals basically unchanged within the A / D conversion time. Then, the A / D converter converts the analog voltage and current signals into digital voltage and current signals that can be processed by the FPGA and transmits them to the FPGA. After receiving the digital voltage and current signals, the control circuit integrated in the FPGA generates a sine wave signal and a cosine wave signal with the same amplitude and frequency as the output voltage of the induction regulator T1. Then, the digital voltage and current signals received by the FPGA are respectively multiplied by the sine wave signal and the cosine wave signal. The results after multiplication are filtered by the low-pass filter integrated in the FPGA to obtain two DC components. Then, these two DC components are respectively multiplied by the sine wave signal and the cosine wave signal. The results after multiplication are inverted and then added to the digital voltage and current signals received by the FPGA, and a signal proportional to the command signal can be obtained. The signal proportional to the command signal is amplified by the FPGA to obtain the command signal. The FPGA transmits the command signal to the trigger pulse generator, and the trigger pulse generator sends out pulse drive to the compensation current generating unit according to the command signal; drives the IGBT or IPM power module of the compensation current generating unit to generate a compensation current with the same amplitude and opposite polarity as the harmonic current of the induction regulator T1 and injects it into the power grid to compensate or cancel the harmonic current and actively eliminate power harmonics.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention can realize the automatic tracking compensation of the voltage waveform of the induction regulator T1 of the test transformer, effectively limit the high-order harmonics, and make the voltage waveform output by the induction regulator T1 as close to a sine wave as possible; according to the actual situation of the construction site, after the application of this filtering and compensation device, the risk of breakdown of the equipment under test during the withstand voltage test can be significantly reduced; at the same time, the active filtering and compensation method can also compensate the capacitive or inductive reactive power during the withstand voltage test, solve the under-compensation or over-compensation phenomenon caused by the parallel connection of capacitors or inductors with a fixed capacity, improve the capacity utilization rate of the test transformer, and avoid the waste of manpower and material resources such as construction period delay and rework caused by defects in the test equipment.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A filtering and compensating device for a test transformer, characterized in that: It includes a harmonic detection unit, an instruction current operation unit, a trigger pulse generation unit, and a compensation current generation unit that are electrically connected in sequence; The harmonic detection unit includes a voltage transformer, a current transformer, and an A / D converter. The voltage transformer and the current transformer are arranged at the output end of the induction voltage regulator for collecting the voltage and current signals output by the induction voltage regulator. The A / D converter is used to convert the analog voltage and current signals into digital voltage and current signals, and send the digital voltage and current signals to the instruction current operation unit; The instruction current operation unit uses a microprocessor. The microprocessor is used to generate an instruction signal according to the received digital voltage and current signals, and send it to the compensation current generation unit; The trigger pulse generation unit uses a trigger pulse generator, which is used to send a pulse drive to the compensation current generation unit according to the instruction signal; The compensation current generation unit is used to generate a compensation current; The harmonic detection unit further includes a sample and hold circuit. The input end of the sample and hold circuit is connected to the output ends of the voltage transformer and the current transformer, and the output end of the sample and hold circuit is connected to the input end of the A / D converter; The microprocessor uses an FPGA. After the FPGA receives the digital voltage and current signals, a sine wave signal and a cosine wave signal with the same amplitude and frequency as the output voltage of the induction voltage regulator are generated by the control circuit integrated in the FPGA. Then, the digital voltage and current signals received by the FPGA are multiplied by the sine wave signal and the cosine wave signal respectively. After multiplication, the results are filtered by the low-pass filter integrated in the FPGA to obtain two DC components. Then, these two DC components are multiplied by the sine wave signal and the cosine wave signal respectively. After multiplication, the results are inverted and then added to the digital voltage and current signals received by the FPGA, and a signal proportional to the instruction signal can be obtained. The signal proportional to the instruction signal is amplified by the FPGA to obtain the instruction signal, and the FPGA transmits the instruction signal to the trigger pulse generator.

2. The filtering and compensating device for a test transformer according to claim 1, wherein: The harmonic detection unit further includes a filtering and amplification preprocessing circuit. The input end of the filtering and amplification preprocessing circuit is connected to the output ends of the voltage transformer and the current transformer, and the output end of the filtering and amplification preprocessing circuit is connected to the input end of the sample and hold circuit.

3. The filtering and compensating device for a test transformer according to claim 1, wherein: The compensation current generation unit uses a single-phase shunt-type bridge converter.

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