FI130856B1 - Method and apparatus for eliminating voltage distortion in electricity distribution network - Google Patents

Abstract

The invention relates to a method for active measurement and filtering of voltage distortion caused by harmonic currents from non-linear loads (L) in an electrical distribution network (AC). Measurement and filtering of the voltage distortion in non-linear loads (L) is carried out by voltage measurement: - by measuring the real value of the voltage (V) from the mains (AC) in phases and removing the distortion-free mains frequency reference value of the voltage, such as the fundamental frequency component (Vref), from the ; and - filtering the resulting voltage distortion into one or more frequency band specific components, such as odd harmonics or the like, after which one or more components of the voltage distortion are amplified (Af1, Af1) on a frequency band basis by means of an adjustable gain (Gf1, Gfn) which can be adjusted separately for each frequency band, are inverted and summed to determine a current reference (iref) for an adjustable power supply (I) that supplies the current corresponding to the current reference (iref) to that mains (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 fundamental frequency corresponding to a sine wave, 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 a sinusoidal current (power), i.e. 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 that can be connected directly to the mains, whose speed is not regulated, are li-

S 25 near loads that are partially inductive & with a power factor cos p between 0.7-0.9. Such

N unregulated linear loads do not impair the voltage quality of the electrical grid. However, inductive and capacitive loads 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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During the last 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 network with other frequencies, different from the network's waveform, 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 harmonics caused by non-linear loads. Surge waves cause a deviation from the basic frequency blue voltage of electricity distribution, i.e. a voltage distortion, whereby 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 electricity network causes local problems, firstly, when the electricity distribution voltage is distorted locally near the non-linear loads, and when the electricity distribution network is overloaded by the surge currents

Because of S 25. Both of the above-mentioned problems eventually cause malfunctions and equipment damage

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Problems caused by surge currents can be compensated

S 30 call using harmonic filters. When the spectrum of harmonic frequencies of the problem = object is unchanged,

The filtering of the most powerful surge voltages and/or currents with frequency-specific 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

AFF measures the surge current caused by the non-linear load in the electrical network and produces a current in phase opposite 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 resonance & resonance oscillation between the AHF and the capacitance, so

The solution here is to rearrange the parameters to produce less or no heat at all. resonate- > Jutta.

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N For some current-controlled active harmonic filters

Self-regulating features have been developed for N tim, with the help of which the device itself is able to analyze the state of the local electricity network 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 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.

Patent publication US 6320392 describes a solution to the problem that arises when using a conventional active harmonic filter, where the response of the compensation current cannot be properly determined due to the continuous change of the network topology. The solution describes a filter device in which the response of the network to harmonic harmonic currents is measured by feeding frequencies deviating from the harmonic frequency into the network and measuring the response caused by these and thereby calculating the response of the compensation. <

S 25 Further in the publication "A Novel Voltage Control for Active Shunt Power Filters" (Zanchetta et al., Industrial Electronics, 2002) describes with the help of voltage measurement: implemented compensation of a single harmonic harmonic wave. The publication describes voltage measurement from the network

S 30 and filtering implemented with a bandpass filter to obtain the 3rd harmonic = harmonic voltage and further

N to determine the amplitude and phase of the compensating current fed into the network. In this context, the publication also describes the determination of the voltage difference for the 3rd harmonic harmonic by removing the fundamental part from the calculated harmonic signal. 5 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 equipment according to the invention are mainly characterized by what is presented in the distinguishing parts of the independent patent claims directed to them.

The basic idea of the invention is, first of all, to eliminate voltage distortion caused by surge currents taken by non-linear loads in the electricity distribution network with an active surge filter, which is based on voltage measurement instead of current measurement. In this case, there is no need for current measurement of the network, but the method and the device work by measuring only the voltage of their connection point. <

S 25 The measurement of the voltage deviation of the electrical network is first carried out using the & reference method, in which case, for example,

Specifically, a mains-frequency, > ideal sinusoidal setpoint signal is subtracted from the actual value of the voltage measured from the power grid. Electricity network

The voltage distortion S 30 is then obtained as the difference between the actual actual value and the ideal reference value.

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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 network's lower fundamental frequency from the signal, and does not cause a phase shift in the remaining harmonic 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 no disturbing fundamental frequency remains after summing the parallel frequency band-specific outputs. If the fundamental frequency still remains after the band-pass filtering and the adder, the fundamental frequency can also be compensated for by arranging the adjustable current source in the control circuit in such a way that it does not produce this fundamental-frequency current into the power grid. < The resulting voltage distortion of the electrical network is further distributed

with S 25 low-pass filters to frequency band-specific components & components, amplified and inverted, i.e.

N will be phased back. The inversion can be performed z at an arbitrary point in the control chain, e.g. after voltage > measurement, after bandpass filtering

S 30 after an adjustable gain or after summing the signal 5. Furthermore, inverting can be

N times before the voltage measurement, in which case the voltage to be measured is already phase-opposed. Thanks to 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 is the simplicity of the voltage measurements made in the method, thanks to which the measurements can be arranged with conventional electrotechnical measurement methods directly from the connection point.

Another advantage of the method and device according to the invention is its adaptability to the variability of the electrical network at the connection point of the active overpass filter. In the control response sense, the connection point in the vicinity of the network can have, for example, < local electricity generation, the connection point's electricity

The S 25 network is low- or high-impedance in relation to & the main network, contains many parallel capacitors

N tight, inductive or non-linear load, z or contains a load above or > below in terms of the electrical network. Adaptability prevents adjustment

S 30 system instability and resonant frequency 5 oscillation, if the loads or characteristics of the electrical network

N change, amplifying 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 at 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 apparatus 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:

Figure 1a shows the general principle of a method and apparatus according to the invention, Figure 1b shows the supplementary general principle of an advantageous method and apparatus according to the invention. <

S 25 The object of the invention is, first of all, a method for removing voltage distortion in the electricity distribution network, which is based on

N for measuring and filtering the voltage deviation produced by the surge currents caused by non-linear loads L, e.g. per phase, from an AC 3 30 with an active surge filter. The removal of the voltage drop is firstly based on the

N referring to the measurement of the voltage from the alternating current network AC with the voltage measurement arrangement V, whereby the measurement result is the actual actual value of the voltage of the power distribution network. The ideal sinusoidal reference value signal Vyes is subtracted from the measured actual value, so after the voltage measurement arrangement, a voltage distortion signal remains, which is fed to at least one bandpass filter BP: . Each bandpass filter BPgszj..BPen has its own frequency passband, so for example a bandpass filter

BPA only lets through the signal of the frequency range fi.

After bandpass filtering, the signal of the defined frequency range is fed to the amplifier Arj, whose gain Ge 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 fn, band-pass filtering with band-pass filter PBs, amplification with amplifier Ar, adjustable gain Gr and opposite phasing with inverter Yr are performed accordingly. All the filtered, amplified and oppositely phased signals are combined in the adder S: into a single sum signal, resulting in the internal current reference i er of the active harmonic filter. The current instruction irer is most advantageously directed to the adjustable power source I realized with power electronics, which feeds the current instruction it receives

A current according to S 25 without phase shift to the power grid

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I As an advantageous application of the method according to the invention, especially with reference to figure 1b, the alternating current network

The actual value of the S 30 voltage is measured with a voltage measuring system 5 V, and the basic

N-frequency part, for example, with a high-pass filter HP:

or with a similar method that filters the basic frequency of the power grid.

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 resonant frequency oscillation of the control system is prevented by adjusting the gain Crn, Cm of the frequency band-specific control amplifier Ar, Ar. If the amplitude of the resonant frequency fi, fn signal is observed to decrease, the gain of the control amplifier Ar, Ar

As Ge, Gen increases, the gain Gray, Gin is adjusted further. On the other hand, if the amplitude of the resonance-frequency fi, fn signal increases Cr,

When Gen is increased, Arj of the control amplifier also increases,

Af, gain Gs, Gm is reduced. <

S 25 As a further advantageous adaptation of the method according to the invention, the frequency-specific control amplifier Af, A:

The adjustment of N gain Gr, Gen is carried out by measuring the amplitude

Based on I background information, automatically when the control values > reach their lower or upper limit. 3 30

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N The method according to the invention, as a further advantageous so-

As an extension of N, the inversion of the signal is carried out with an inverter Y at a freely chosen point in the control circuit, e.g. before the voltage measurement arrangement V,

Veer, before band-pass filter PBs, PBs, after band-pass filter PBs, PB: before adjustable amplifier An, Arm, after amplifier An, Ar, or after adder 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: - essentially a voltage measurement arrangement V, Vier connected to the electricity distribution network AC to measure the actual value of the voltage and the voltage difference, - at least one frequency-specific band-pass filter

BPs: to filter the frequency-specific signal of voltage distortion caused by harmonic harmonics, - amplifier Ar, Ar equipped with adjustable gain CA, C for each separate band-pass filtered frequency to increase or decrease the signal amplitude to compensate for changes caused by fluctuations in the electrical network of the connection point,

S 25 - inverter Ys, Ys for inverting & inverting the voltage signal,

N - signal adder S: for combining the oppositely phased signals £i..fn into one sum signal and further to obtain the current instruction ireg,

S 30 - and adjustable current source I according to the current instruction i,.r = for supplying current to the electricity distribution network AC without

N essential phase shift.

As an advantageous application of the equipment according to the invention, in connection with it, the high-pass filter HPs arranged in connection with the voltage measurement arrangement is essentially connected to the network.

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 any given time for filtering the basic frequency of the network, such as RC,

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 with component choices to increase cost efficiency and to highlight and modify the required properties. It is clear < that for measuring and filtering the voltage deviation can

The S 25 can be used with digital or analog components, as well as using automatic, sensor or

Computer-controlled control solvers based on N

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Claims (9)

Patent Claims 1. A method for actively measuring and filtering the voltage distortion caused by the surge currents taken by the non-linear loads (L) of the electric distribution network (AC) in the electric distribution network (AC), whereby the measurement and filtering of the voltage distortion in connection with the non-linear loads (L) is carried out by voltage measurement (V): — measuring the actual value of the voltage phase-by-phase from the electricity distribution network (AC) and by removing from it the undistorted, network-frequency reference value of the voltage, such as the basic frequency component Veer; 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; characterized by the fact that one or more components of the voltage difference (fi, fn) are amplified (Arn, Ar) for each frequency band using separately adjustable gain (Ge, Gm) for each frequency band, inverted and summed to obtain the current reference (ireg) S 25 for an adjustable current source (I), which supplies the current according to the current & current instruction (ireg) to the electricity distribution network N (AC). 7 O 3 30 2. The method according to claim 1, characterized by removing = the fundamental frequency part of the voltage from the actual value of the voltage with a high-pass filter (HPs), with a band-pass filter (PBs:, PB), or similar. 3. The method according to claim 1 or 2, characterized by the fact that the gain (Gr, Gen) of each frequency-band-specific component (fi, fn) of the voltage difference is set higher if increasing the gain (Gr, Gen) reduces the amplitude of the frequency-band-specific component and lower if the gain - increasing the voltage (Gs, Gm) increases the amplitude of the voltage difference component (fi, fn). 4. The method according to claim 3, known for the fact that the gain (Crn, Cm) of each frequency band-specific component is adjusted automatically. 5. The method according to one of the preceding patent claims 1-4, characterized in that the voltage distortion measured from the electrical network is amplified and inverted to obtain the current instruction (irer) and is directed to the current source (I), which feeds the current according to the current instruction (irers) into the electrical network (AC) without substantial phase shift. x < 25 6. The method according to claim 5, characterized by the fact that the current source is preferably implemented with N power electronics. 7 © 7. Equipment for the active measurement and filtering of voltage distortion caused by surge currents taken by non-linear 3 30 loads of the electricity distribution network, characterized in that the equipment comprises means for measuring and filtering surges by means of voltage measurement on a phase-by-phase basis, which means at least a voltage measurement arrangement (V, Veer), at least one frequency-specific band-pass and/or band-stop filter (PB::, PB-n), frequency-band-specific and with adjustable gain (CF, Cm) V-equipped amplifier (Af, Am), frequency-band-specific signal inverter (Ys), signal adder ($ Sz) and adjustable current source (I). 8. Apparatus according to claim 7, 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). 9. Apparatus according to claim 7 or 8, characterized in that it includes elements for identifying amplitude changes of frequency band-specific signals (fi..f,) in order to determine frequency band-specific adjustable gain (Gr, Gm). <t N O N 0 <Q N N I a a © O 0 To N O N