FI20215806A1 - Method and apparatus for eliminating voltage distortion in electricity distribution network - Google Patents

Abstract

The object of the invention is a method for the active measurement and filtering of voltage distortion in the electrical network (AC) caused by the surge currents taken by the non-linear loads (L) of the electrical distribution network. The measurement and filtering of voltage distortion in connection with non-linear loads (L) is carried out by voltage measurement: - by measuring the actual value of the mains voltage (V) phase-by-phase from the electric network (AC) and removing from it the undistorted, mains-frequency reference value of the voltage, such as the fundamental frequency part (Vref); and - by filtering the obtained voltage distortion into one or more frequency band-specific components, such as odd harmonic harmonics or the like, after which one or more components of the voltage distortion are amplified (Af1, Af1) per frequency band using separately adjustable gain (Gf1, Gfn) for each frequency band, inverted and summed, current instruction ( iref) to obtain an adjustable current source (I) that supplies a current according to the current instruction (iref) to the electrical network (AC).

Description

Method and equipment for eliminating voltage imbalance in the electricity distribution network

The object of the invention is the method and apparatus for eliminating voltage imbalance in the electricity distribution network according to the preambles of the independent patent claims that apply to it.

AC power distribution in the power grid generally takes place with a sine wave % fundamental frequency, which is most commonly 50Hz or 60Hz. Electrical loads that draw sinusoidal current (power) at this same frequency are linear loads. Linear loads can be resistive, such as, for example, heating resistors used in direct electric heating. On the other hand, electrical loads that take sinusoidal current (power) or at the fundamental frequency, but are in phase shift with respect to the voltage, are inductive (inductances) or capacitive (capacitors) linear loads.

Electric motors are still the most common electrical loads among linear loads. Motors connected directly to the mains, whose speed is not regulated, are 1li-

S 25 near loads that are partially inductive

K with the power factor cos p between 0.7 and 0.9. Such unregulated linear loads do not impair the voltage quality of the power grid. Inductive and capacitive

E tight loads, however, cause reactive power and

S 30 weaken the efficiency of the electricity distribution network and at the same time limit the maximum power transmission.

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Over the past decades, motor drives and other regulated electrical devices adjusted to improve the efficiency of the use of electrical energy have become common in the electrical network, for example in the form of frequency converters, rectifiers, computers and televisions. In addition to the basic frequency, such regulated electrical drives take current from the electrical grid with other frequencies, deviating from the waveform of the grid, and they are called non-linear loads. Currents deviating from the fundamental frequency of the network are called harmonic currents, which are caused by harmonic harmonic waves caused by non-linear loads. Surge waves cause a deviation from the basic frequency blue voltage of electricity distribution, i.e. a voltage distortion, in which case the high-power electrical loads that draw surge current from the power grid significantly change the shape of the distribution voltage curve locally. This results in the fact that the quality of the electricity network no longer meets the requirements set for it.

The increasing amount of non-linear load and surge current in the power grid causes local problems, firstly, when the electricity distribution voltage is distorted locally near non-linear loads, and when the power distribution network is overloaded by surge currents

Because of S 25. Both of the above-mentioned problems cause

K eventually causes malfunctions and equipment damage in electrical equipment. j

Problems caused by harmonic currents can be compensated > 30 by using harmonic filters. When the spectrum of over-wave frequencies of the problem = object is unchanged, & filtering of the most powerful over-wave voltages and/or currents with frequency-specific designed passive filters works well. Furthermore, if the frequency spectrum and amplitude of the harmonics of the problem object vary, then an active harmonic filter (AHF, Active Harmonics) is generally used as a solution to problems caused by harmonics

Filter).

A conventional active harmonic filter (AHF) works on the principle of current measurement and regulation. Power adjustable

AHF measures the surge current caused by a non-linear load in the electrical network and produces a current in opposite phase to the surge current, feeding it into the electrical network. In this way, the sum of the surge currents at the connection point of the AHF is reduced and the resulting voltage distortion is reduced. In order for the AHF to work efficiently, it must be adjusted and set (parameter setting) to suit the electrical environment of the application.

Without expert setup during commissioning, a conventional AHF can amplify harmonics of a certain frequency instead of attenuating them. Furthermore, if substantial changes are made in the local electricity network after commissioning, the current-controlled AHF must be adjusted again to correspond to the changed conditions. For example, the addition of large capacitance near

S 25 connection points of the current-regulated AHF cause reso-

Between the AHF and the capacitance of the K nancial oscillation, which

The solution I found is to rearrange the parameters to produce less or no ko. resonant

No shit.

S 30

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N Self-regulating features have been developed for some current-regulating active surge filters & tims, which enable the device itself to analyze the state of the local power grid and adjust itself accordingly if necessary. In some cases, it is also possible to react to changes in the electrical environment of the object of use through the measurement of the electrical network via a remote connection and the parameter setting of the AHF. Regardless of the method, the usual current control

The installation of AHF's current sensors, the parameter setting based on the measurements of the electrical network and the possible resetting are availability-critical work that requires expertise and quality, which substantially increases the costs of network disturbances caused by surges.

The purpose of the method and equipment according to the present invention, which are used for removing the voltage imbalance of the electricity distribution network, is to bring about a decisive improvement to the problems presented above and thus substantially raise the state of the art prevailing in the field. In order to realize this purpose, the method and apparatus according to the invention are mainly characterized by what is presented in the distinguishing parts of the independent patent claims directed to them.

S 25 The basic idea of the invention is, first of all, to remove electrical

K voltage distortion caused by surge currents taken by non-linear loads with an active surge filter based on current

E instead of measurement for voltage measurement. In this case, ver-

With the S 30, no current measurement is needed, but the method and = device work by measuring only the voltage of their connection points.

The measurement of the voltage deviation of the electrical network is first of all carried out using the reference method, whereby, for example, a grid-frequency, 5-ideal sinusoidal reference value signal is subtracted from the real actual voltage value measured from the electrical network. The voltage distortion of the electrical network is then obtained as the difference between the actual actual value and the ideal reference value.

If the ideal blue reference value is not available or cannot be used, a high-pass filter, an ideal band-pass filter or a similar signal modifying method can be used to help measure the voltage difference. When using one or more high-pass filters, the actual value of the voltage is measured from the power grid, for example per phase, after which the signal is filtered with a high-pass filter, which removes the lower fundamental frequency of the network from the signal, and does not cause a phase shift in the remaining wave frequencies. After high-pass filtering, the remaining signal is the voltage distortion of the electrical network. When using ideal frequency band-specific band-pass filters, on the other hand, the fundamental frequency of the network is attenuated so much that it does not leave a disturbing fundamental frequency from the point of view of the control circuit

After summing the outputs per S 25. If pe-

There is still some frequency remaining after bandpass filtering and the adder, the base frequency can be compensated by arranging the adjustable current source in the control circuit below in such a way that it does not produce this 5 30 base frequency current into the electrical network. a

N The obtained voltage distortion of the electrical network is further divided by band-pass filters into frequency band-specific components, amplified and inverted, i.e. oppositely phased. The inversion can be performed at any point in the control chain, e.g. after voltage measurement, after bandpass filtering, after adjustable gain, or after summing the signal. Furthermore, the inversion can be performed before the voltage measurement, in which case the voltage to be measured is already phase-opposed. As a result of the above, a signal corresponding to the voltage distortion, but in opposite phase when inverted, is obtained, from which the internal current reference of the active harmonic filter according to the invention is obtained. This internal current instruction is controlled

To the adjustable current source belonging to the AHF device, preferably implemented with power electronics, which feeds the current according to the current instruction received into the electrical network. The current supplied by the power source to the electrical network in opposite phase to the voltage difference thus adjusts the voltage difference to a small one.

The most important advantage of the method and equipment according to the invention should be mentioned firstly the simplicity of the voltage measurements made in the method, thanks to which the measurements can be arranged with conventional electrical measurement methods directly at the connection

N out of 25 points.

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<Furthermore, as an advantage of the method and device according to the invention, its adaptability to the electrical network at the connection point of the active overpass filter should be mentioned

S 30 for variability. In terms of control response, the network at the connection point may have, for example, & local electricity production nearby, the connection point's electrical network is low- or high-impedance in relation to the grid, contains a lot of parallel capacitive, inductive or non-linear loads, or contains loads above or below the power grid . With the help of adaptability, instability of the control system and resonant frequency oscillation are prevented, if the loads or characteristics of the electrical network change, strengthening some frequencies. Adaptivity is implemented with the mentioned frequency band-specific bandpass filters and adjustable amplifiers. If the control system becomes unstable, the amplitude of the voltage oscillation increases with the resonance frequency. With the help of the method and equipment according to the invention, the system can be stabilized by adjusting the gain of the amplifier specific to the frequency band.

Other advantageous applications of the method and equipment according to the invention are presented in the independent patent claims directed to them.

In the following explanation, the invention is illustrated in detail by referring to the attached drawing, in which:

In the picture, Sat

S 25 shows a method according to the invention

N and the general principle of the equipment, 3 > in figure 1b

E is presented the supplementary general principle of the 5 30 method and equipment according to an advantageous invention

N aate.

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The object of the invention is, first of all, a method for removing voltage distortion in the power distribution network, which is based on measuring and filtering the voltage distortion produced by the surge currents caused by nonlinear loads L, e.g. per phase from the alternating current network with an active surge filter. The removal of the voltage spike is based, first of all, on the measurement of the voltage from the alternating current network AC with the voltage measurement arrangement V, with reference to the one shown in figure la, so that the measurement result is the actual current value of the voltage of the power distribution network. The ideal sinusoidal reference value signal Vier is subtracted from the measured actual value, so that after the voltage measurement arrangement, a voltage distortion signal remains, which is fed to at least one bandpass filter BPs. Each band-pass filter BP:j..BPey has a specific frequency pass band, so for example a band-pass filter

BPA allows only the fi frequency range signal to pass through.

After bandpass filtering, the signal of the defined frequency range is fed to the amplifier An, whose gain Gg can be adjusted with a regulator. After amplification, the filtered and amplified signal is reverse-phased with the inverter Ys. For each desired frequency band f, a bandpass

S 25 work filtering with band pass filter PB, amplification

K with amplifier Af, adjustable gain Gr and

I reverse phasing with inverter Yen. All filtered, amplified and counter-phased sig-

E lit are combined in the adder S: into one sum signa-

S 30 lix, which gives the iier of the active harmonic filter = internal current instruction. The current instruction i;eg is preferably directed to the adjustable current source I implemented with power electronics, which feeds the current according to the received current instruction without phase shift into the AC power grid.

As an advantageous application of the method according to the invention, especially with reference to figure 1b, the actual value of the voltage of the AC network is measured with a voltage measurement system V, and the fundamental frequency part is removed from the actual value of the voltage, e.g. with a high-pass filter HP or a similar method for filtering the fundamental frequency of the electrical network.

As a further advantageous application of the method according to the invention, the harmonic harmonic disturbances of the electrical network are removed by selecting the frequency bands of the harmonic harmonics of the electrical network as the frequency bands of the band-pass filters, such as the frequencies of the odd (1st, 3rd, 5th, etc.) harmonics, and by setting a separate gain for each frequency , which is regulated.

As a further advantageous application of the method according to the invention, the gain Gg, Gm of the frequency-specific control amplifier Af, Ae is first adjusted to be greater, if the amplitude of the respective frequency fi, fn decreases

S 25 control amplifier Ag, Ag gain Crn, Gm increase-

K here. On the other hand, if the amplitude of the signal of frequency fi, fn increases, the gain = Ge, Gen of the control amplifier An, Arm is reduced. a ©

S 30 As a further advantageous adaptation of the method according to the invention, the frequency-specific control amplifier Arn, Arm

The adjustment of N gain Gg, Gm is carried out based on the amplitude measurement data automatically when the adjustment values reach their lower or upper limit.

As a further advantageous application of the method according to the invention, the inversion of the signal is carried out with an inverter at a freely chosen point of Y in the control circuit, e.g. before the voltage measurement system V, Vier, before the band-pass filter PB, PBfn, after the band-pass filter PB:,, PB, before adjustable amplifier Ag, Am, after amplifier An, Af, or after summer S:.

The object of the invention is, on the other hand, an apparatus for removing voltage distortion in the electricity distribution network, which is based on measuring and filtering the voltage distortion, for example, phase-by-phase from the alternating current network. The equipment intended for measuring and filtering the voltage difference includes a voltage measurement arrangement V, Vier essentially connected to the electricity distribution network AC for measuring the real actual value of the voltage and the voltage difference, at least one frequency-specific bandpass filter BP:,; to filter the frequency-specific signal of voltage distortion caused by harmonic harmonics, for each band-pass filtered frequency a separate

S 25 whistle An, Am with adjustable gain Gr, Gen

K to increase or decrease the amplitude of the signal

First, in order to compensate for the changes caused by fluctuations in the electrical network of the connection point, to phase the voltage signal of the inverter , Yr, Ye in the opposite direction,

S 30 for combining the oppositely phased signals = fi..fn of the adder Sg into a single sum signal and further current reference i,er, and the adjustable current source I for supplying the current according to the current reference i,.r to the electricity distribution network AC without significant phase shift.

As an advantageous application of the equipment according to the invention, in connection with it, a high-pass filter HP: is connected to the mains and substantially arranged in connection with the voltage measurement arrangement.

As a further advantageous application of the equipment according to the invention, the adjustable current source I does not produce the basic frequency of the electrical network for the current supplied to the network according to the current instruction i,.r.

It is clear that the invention is not limited to the applications presented or explained above, but can be modified within the framework of the basic idea of the invention, depending on the circumstances, by using in the method the type of filter best suited to the purpose at the time for filtering the basic frequency of the network, such as RC-, RI-, LC- , LCL, Chebyshev, Butterworth, Bessel or

Cauer filter or a similar signal modifying filter. In the design of the electronic circuit that implements the basic idea of the method and the equipment, the method of implementation can be modified by component choices, cost-

S 25 to increase operational efficiency and meet the required characteristics

To highlight and modify the features. It is clear that digital or analog components can be used to measure and filter the voltage difference, as well as make use of automatic, sensor or

S 30 computer-controlled control solutions based on similar ones.

OF

Claims (12)

Patent Claims 1. A method for the active measurement and filtering of the voltage distortion caused by the surge currents taken by the non-linear loads (L) of the electrical distribution network (AC) in the electrical distribution network (AC), characterized by the fact that the measurement and filtering of the voltage distortion in connection with the non-linear loads (L) is carried out by voltage measurement ( V): — by measuring the actual value of the voltage phase-by-phase from the electricity distribution network (AC) and subtracting from it the undistorted, network-frequency reference value of the voltage; and — by filtering the obtained voltage distortion into one or more frequency band-specific components (fl..fn), such as odd harmonic harmonics or the like; and in which connection the frequency band-specific signal (fi, fn) is amplified and inverted and summed to obtain a current instruction (lier) for the adjustable current source (I), which supplies a current according to the current instruction (i,.r) — to the electricity distribution network (AC). Oh 25 OF 2. The method according to claim 1, known for the fact that the measurement of the voltage difference is carried out Ek by measuring the actual value of the voltage from the electrical network (AC) and c by removing the fundamental frequency part (Vier) from it. 8 30 OF 3. The method according to claim 2, known for removing the fundamental frequency part of the voltage from the actual value of the voltage with a high-pass filter (HPs), with a bandpass filter (FB, PB), or similar. 4. The method according to one of the previous patent claims 1-3, characterized in that the voltage distortion is divided into one or more components per frequency band. 5. The method according to one of the preceding claims 1-4, characterized in that each frequency band-specific component of the voltage difference is amplified separately. 6. The method according to one of the preceding patent claims 1-5, characterized in that the gain of each frequency band-specific component is adjusted. 7. The method according to claim 6, known for the fact that the gain (Gz1, Gen) of each frequency band-specific component is adjusted higher as the signal amplitude decreases, increasing the gain (Gr, Gen) and lower as the signal amplitude increases. S 25 N 8. The method according to claim 7, known for the fact that the gain (Gz1, Gm) of each frequency band-specific component is adjusted automatically. Oh 30 N 9. The method according to one of the preceding patent claims 1-8, characterized in that the voltage distortion measured from the electrical network is amplified and inverted to obtain the current instruction (i,er) and is most suitably directed to a current source (I) implemented with power electronics, which supplies a current according to the current instruction (irer) to the electrical network (AC) without significant phase shift. 10. equipment for the active measurement and filtering of the voltage difference caused by surge currents taken by non-linear loads of the electricity distribution network, characterized in that the equipment comprises devices for measuring and filtering surges by means of voltage measurement on a phase-by-phase basis, which devices include at least a voltage measurement arrangement (V, Vier), at least one frequency-specific band-pass and/or band-stop filter (PB:1, PB), amplifier (Ag, Af) equipped with frequency band-specific and most suitable adjustable gain (Gg, Gm), frequency-band-specific signal inverter (Ye), signal adder ( Sg) and an adjustable current source (I). 11. Apparatus according to claim 10, known for the fact that a high-pass filter (HP¢) is arranged in connection with the voltage measurement arrangement (V) to filter the basic frequency of the electrical network (AC). Oh 25 12. The equipment according to claim 10 or 11, characterized in that it includes elements + for identifying the amplitude changes of frequency band-specific signals (fi..f,) to determine the frequency band-specific c adjustable gain (Ge, Gm). 8 30 3