SU505118A1 - Device for adjusting linear filter - Google Patents

Description

one

The invention relates to devices serving to suppress higher harmonic components present in a voltage spectrum on higher voltage lines or buses, and can be used in conversion stations of direct current transmissions.

It is known 1 that 1V-voltage converters generate higher harmonics both on the DC side (even harmonics) and on the AC side (odd harmonics, nth, seventh, eleven, trine adc, etc.).

Harmonics cause additional losses, for example, in generators and transformers. An effective measure to combat them is bypassing them with the help of filters tuned to resonate at the selected harmonic frequency.

The filters used are a serial connection of a capacitor bank and a reactor.

However, these filters cannot be tuned exactly in resonance to this harmonic due to changes in both environmental parameters, possible changes in the number of capacitors in the battery, and due to the instability of the frequency of the main harmonics of the AC network, and hence all the main harmonics

To adjust the filters to resonance for a given harmonic, the filters must be adjustable. It is most convenient to adjust the filters by changing the inductance of the reactor.

The inductance of the reactor can be changed in two ways: smoothly and in steps.

A gradual change in reactor inductance is achieved by magnetising it.

direct current, and stepwise - by changing the number of turns of its winding.

A known device for regulating the linear filter 2 comprises a measuring unit. The first input of this block receives signals from the Current sensor installed in the linear filter circuit, and the second through the resonant amplifier from the output of the sensor of the AC bus voltage. The output of the measuring unit through the control unit is connected to the switch unit of the taps connected to the winding of the controlled reactor.

The known device is based on measuring the reactive power of a linear filter.

for a given harmonic and keep this power to a minimum by changing the inductactic reactor.

However, in such a device, the voltage from the output of the tire voltage sensor of alternating current is fed to the input of the measuring

block through a resonant filter. The calculated value of the reactive power depends on the stability of the magnitude and phase of the output voltage of this resonant filter. may have a deviation from nominal on

Taking into account that the frequency in the supply system may have a deviation of ± 1 Hz from the nominal, the phase and amplitude of the output voltage of the filter vary significantly. For example, when the quality of the filter changes the phase shift L 50 ° el., And the amplitude is 20% at the harmonic frequency when the network frequency changes from 50 to 49 Hz.

Thus, a change in the frequency in the power supply converter of the network leads to a false change in the reactive power and to a forced detuning of the power resonance of the filter, which is unacceptable.

In order to eliminate this drawback, a device has been developed that allows the linear filters to be adjusted with the necessary accuracy when reactors with stepwise inductance are installed in their circuits, regardless of the frequency drift of the AC network, as well as from changes in the environmental parameters and the number of capacitors battery

In the proposed device for adjusting the linear filter, this is achieved due to the presence of two synchronization units, the output of the current sensor installed in the linear filter circuit is connected to the input of one of the synchronization circuits, the output of the sensor is an alternating current voltage to the input of the second synchronization circuit, and the outputs both timing circuits are connected to the inputs of the measuring unit.

Diagram of the device shown in the drawing.

Device for regulating a linear filter connected to AC buses and made of a capacitor bank 1 and an adjustable filter reactor

2c taps on the winding, contains a sensor

3taka 1B linear filter circuits, sensors for ac busbars, measuring unit 5, control unit 6, spurs switching unit 7, synchronization blocks 8, 9.

The device operates as follows.

A signal proportional to the current flowing through the linear filter circuit from the current sensor 3 is supplied to the input of the synchronization unit 8. A voltage is formed on the output of this unit, the frequency of which is equal to the frequency of the harmonic suppressed by the filter, and

the phase of the voltage is shifted by an angle with respect to the phase of the current of a given harmonic flowing through the linear filter circuit.

As block 8, 3 synchronization blocks can be used, containing a phase discriminator. The discriminator output is connected via an integrator to the input of the controlled generator, and the generator in turn is connected to the second input of the phase discriminator, the first input of which is supplied with signals from current sensors 3 installed in the linear filter circuit.

Such a closed synchronization circuit with a controlled oscillator, the natural frequency of which is close to the frequency of the extracted harmonic, allows to receive a signal of this harmonic at the output of the controlled oscillator, and the phase of this signal differs from the phase of the current of this harmonic, flowing „v

through the linear filter circuit "and the angle -

Voltage whose frequency is equal to the frequency of the harmonic suppressed by the filter, and

phase shifted by angle

to the current phase of a given harmonic flowing through a linear filter circuit, from the output of the synchronization unit 8 goes to one of the inputs of the measuring unit 5, to the other

the input of which is supplied from the synchronization unit 9 connected to the output of the sensor 4 of the AC bus voltage.

As block 9, a synchronization circuit can be used, consisting of a phase discriminator, an integrator, and a controlled oscillator.

In this case, one of the inputs of the phase discriminator of the synchronization unit is connected

with the output of the sensor voltage 4 AC tires. As a result, a voltage is generated at the output of the synchronization unit 9, the frequency of which is equal to the frequency of the harmonic suppressed by the linear filter;

this phase of the output voltage is shifted

by angle - with respect to phase eg i

nor, the harmonic suppressed by the linear filter.

The voltages from the outputs of both synchronization blocks are fed to the corresponding inputs of the measuring unit 5. The measuring unit is designed to determine the phase and the magnitude of the shift angle between the stresses I received at its inputs from the synchronization blocks 8 and 9, i.e., to determine the phase and shear angle with current and voltage harmonic frequency of a linear filter.

When measuring, the voltage of the harmonic of the tuning frequency of the linear filter is taken as the reference voltage, i.e. the voltage from the output of the synchronization unit 9 to one of the inputs of the measuring unit 5.

The measuring unit can be made on the basis of the phase meter 4.

When the linear filter is tuned to voltage resonance, the inputs to the measuring unit 5 from the synchronization blocks 8 and 9 coincide in phase, with the result that there is no signal at the output of the measuring unit. In case of linear filter detuning

between the voltages supplied to the inputs of the measuring unit 5 from the synchronization blocks 8 and 9, a shear angle appears, the magnitude of which is paiBHa to the shear angle between the current and the voltage harmonic of the linear filter tuning frequency.

If the harmonic current frequency of the tuning of the linear filter is ahead of its voltage, then the output of the measuring unit 5 is a signal of one polarity, if the current is lagging, the other polarity.

The magnitude of the output signal of the measuring element is proportional to the angle between the current and the voltage harmonic of the tuning frequency of the linear filter. The signal from the output of the measuring unit through the control unit 6 is fed to the input of the switch unit 7 of the taps, which, depending on the polarity and magnitude of the signal, turns on the corresponding tap of the reactor.

Claims (4)

1. Posse A. Century Schemes and modes of transmission of direct current. “Energy, 1973. 2. The patent of France No. 1538745 on cl. H02J. 3. V. Bukhviner. Discrete circuits in phase radio communication systems. “Holy bones, 1969. 4.Shtl Ndin V.M. Digital measuring transducers tt appliances. “Higher School, 1973.