WO2006068495A2 - Device for reducing harmonics - Google Patents

Device for reducing harmonics Download PDF

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Publication number
WO2006068495A2
WO2006068495A2 PCT/NO2005/000468 NO2005000468W WO2006068495A2 WO 2006068495 A2 WO2006068495 A2 WO 2006068495A2 NO 2005000468 W NO2005000468 W NO 2005000468W WO 2006068495 A2 WO2006068495 A2 WO 2006068495A2
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WO
WIPO (PCT)
Prior art keywords
core
winding
wound around
magnetic core
inductor
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PCT/NO2005/000468
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French (fr)
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WO2006068495A3 (en
Inventor
Bjørnar Skaar JOHANSEN
Christian Magnus Hartmann
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Magtech As
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Publication of WO2006068495A2 publication Critical patent/WO2006068495A2/en
Publication of WO2006068495A3 publication Critical patent/WO2006068495A3/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
    • H01F27/38—Auxiliary core members; Auxiliary coils or windings
    • H01F27/385—Auxiliary core members; Auxiliary coils or windings for reducing harmonics

Definitions

  • the present invention relates to devices, a method and a system for reduction of harmonics.
  • the present invention relates to reduction of third harmonics in a device for voltage control and/or voltage stabilisation of a three- phase power supply.
  • the European standard EN50160 "Voltage characteristics of electricity supplied by public distribution systems” sets, among other things, a maximum level for THD and harmonics for voltage supplied to consumers.
  • the invention provides a device for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of, for each phase, an autotransformer with a first magnetic core, a series winding and a parallel winding, and a circuit element with a non-linear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said device comprising: one third winding for each phase, wound around said first magnetic core of the autotransformer, wherein said third windings are connected to each other in a delta configuration.
  • each non-linear circuit element is a variable inductor connected to the autotransformer, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized.
  • This variable inductor and its connection to the autotransformer are described in WO 2004/053615.
  • the invention is, however, intended to also cover use of other nonlinear devices such as a transformer or other saturable devices, a triac, a thyristor, a rectifier device, or an arcing device.
  • nonlinear devices such as a transformer or other saturable devices, a triac, a thyristor, a rectifier device, or an arcing device.
  • the nonlinear circuit elements cause harmonic components to be injected into the autotransformer, because of their nonlinear voltage-current characteristics.
  • the injected harmonic components result in undesirable harmonic flux components in the first magnetic cores, and since the loads are all connected to a common ground, harmonic currents will run through the loads to ground.
  • this induced current is limited by the connection of a decoupling inductor included in the delta configuration.
  • the dimensioning of the decoupling inductor will have to be based on a compromise between the wish to counteract load unbalance on the one hand, and the need for reduction of 3 rd harmonics on the other. If the decoupling inductor has a high inductance, the level of 3 rd harmonic will not be reduced sufficiently; if it is too low, it will not be possible to control the voltages of each phase independently. It is an object of the invention to provide a satisfactory compromise between these requirements, and more specifically to comply with the limits established by international and national standards, such as e.g. EN50160 and other IEC, IEEE or European standards, or national regulations (e.g. the Norwegian "Forskrift om leveringskvalitet i kraftsystemet").
  • the decoupling inductor is variable, and in one variant of this embodiment, the decoupling inductor comprises a magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, such that the inductance of the decoupling inductor is controllable by the current flowing in the control winding.
  • an autotransformer system for IT grids can result in asymmetric load voltages in certain load situations. This is partly due to the control system consisting of three independent PI controllers, each of them measuring one load voltage (line-line) and controlling one of the three line currents.
  • a load (line-line) voltage may be regarded as a result of two line currents through a load impedance (between two phases), the effective load voltage is then controlled by two independent controllers.
  • This concept can lead to worse operating conditions for the variable inductor with increased THD in addition to unnecessary asymmetric load voltages.
  • a third winding wound around said second core a winding which is adapted to create a magnetic field with the same direction as the main field
  • the performance of the autotransformer system can be enhanced.
  • the invention also relates to a method for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of for each phase, an autotransformer with a first magnetic core, a series winding and a parallel winding, and a circuit element with a non-linear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said method comprising the steps of: - providing, for each phase, a third winding wound around the first magnetic core, and
  • the non-linear circuit element is a variable inductor connected to the autotransformer, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized.
  • it is a transformer, or other saturable devices, or a triac, a thyristor, a rectifier device, a saturable device, or an arcing device.
  • the method further comprises the step of including a decoupling inductor in the delta configuration, and in a variant of this method, it comprises varying the inductance of the decoupling inductor.
  • the decoupling inductor comprises a third magnetic core, a second main winding wound around the core and a second control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, such that the inductance of the decoupling inductor is controllable by the current flowing in the control winding.
  • the method comprises regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
  • the method comprises controlling decoupling of the voltages of the three phases from one another by strongly unbalanced loads by varying the inductance of the variable inductor.
  • the method comprises reducing third harmonics and other zero sequence harmonics and regulating the level of symmetric output voltages with strongly unbalanced loads by varying the inductance of the variable inductor.
  • the invention also relates to a device for voltage stabilisation of a three-phase supply, comprising a device according to the invention as described above for reducing harmonics in the delivered voltage resulting from any harmonic component of the magnetic flux in the magnetic core of the autotransformer injected by the non-linear circuit element.
  • the invention comprises also a regulating system for voltage stabilisation of a three-phase power supply, the regulating system comprising a voltage stabilisation device according to the invention, and comprising measuring units for output voltage and current for each phase, an input unit and a processing unit for, based on the measured output voltage and current for each phase and on the threshold values, varying the inductance of the decoupling inductor.
  • the decoupling inductor comprises a third magnetic core, a second main winding wound around the core and a second control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, and the processing unit comprises means for regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
  • the input unit is adapted to receive threshold values for third degree harmonics and the processing unit is adapted to based on measured values and on third degree harmonics thresholds, to vary the decoupling inductor's inductance.
  • the input unit is adapted to receive threshold values related to symmetry and the processing unit is adapted to based on measured values, on third harmonics thresholds and on symmetry thresholds, to vary the decoupling inductor's inductance.
  • Figure 1 shows a system for voltage stabilisation of a power supply line in a TN network mainly according to WO 2004/053615.
  • Figures 2A and 2B show a device according to the invention.
  • Figures 3 and 4 show third harmonics and third harmonic distortion for three-phase load.
  • Figures 5 and 6 show a regulating system according to the invention.
  • Figure 7 shows an embodiment of the invention where each variable inductor comprises a winding included in the delta.
  • Figure 1 shows a system for voltage stabilisation of a power supply line.
  • the system mainly corresponds with that described in WO 2004/053615, and the respective elements will therefore not be described in detail.
  • Inductors Ll, L2 and L3 are not described in said publication, and neither are they a part of the present invention. Their function is to reduce harmonics and enhance performance with non-symmetric loads.
  • load Z, generators Gl, G2 and G3, and the primary windings of autotransformers Tl, T2 and T3 are connected in star configuration to a neutral (TN network). This system will show an unacceptably high level of THD.
  • Figures 2A and 2B show a device 1 for voltage stabilisation of a three-phase supply, comprising, for each phase: - an auto transformer Tl, T2, T3 with a first magnetic core 2, 3, 4, a series winding NsI, Ns2, Ns3 and a parallel winding NpI, Np2, Np3, - a variable inductor T4, T5, T6 connected to the autotransformer Tl, T2, T3 respectively, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized.
  • the figure also shows, for each phase, a third winding NdI, Nd2, Nd3 wound around the first magnetic core 2, 3, 4 respectively, where the third windings associated to each phase NdI, Nd2, Nd3 respectively are connected to one another in delta configuration, and a decoupling inductor Bl connected in series with said delta configuration.
  • the figure also shows parallel inductors Ll, L2 and L3.
  • Figure 2B shows a device according to the invention in a TN network.
  • the third windings NdI, Nd2 and Nd3 are wound about the first magnetic cores 2, 3, 4 respectively such as to create magnetic fields which are mainly parallel to the magnetic fields created by series and parallel windings NsI, Ns2, Ns3 and NpI, Np2 and Np3 respectively.
  • the decoupling inductor Bl can be variable.
  • the decoupling inductor comprises a magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, and the decoupling inductor is adapted to vary the decoupling inductor's inductance by means of the control current.
  • a variable inductor which can be used in the present device is e.g. described in WO 2004/053615.
  • Figures 3 and 4 show results of experiments on a TN network provided with a device according to the invention.
  • Figure 3 illustrates variation of the third harmonic content in output voltages with three phase symmetric load, with and without the device according to the invention.
  • the line voltage was 400V
  • the line current was varied between 0 and 80A
  • the load was varied between 0 and 30KW.
  • Figure 4 illustrates THD for the same load steps. Typically a value of 5mH (at 50 Hz) for the decoupling inductor was sufficient to ensure performance in accordance with standard EN50160 for a wide range of loads.
  • this inductor represents a trade off between attenuation of 3 rd harmonics and decoupling of the phases, and the preferred value for the inductor is a design parameter that must be determined based on this and other design criteria.
  • the device was also tested with single phase loads, and even under these circumstances there were no harmful voltage levels between the unloaded phases as long as the decoupling inductor (5mH) was present in the delta configuration.
  • the inductance can be increased in case of open circuited (phase) loads. In this manner the no-load phase can be decoupled from the others and a good voltage control of these phases can still be maintained.
  • FIGS 5 and 6 illustrate a regulating system according to the invention.
  • Said system 5 for voltage stabilisation systems for three-phase power supply comprises a device according to the invention. It also, comprises measuring units 6, 7, 8, 9, 10, 11 for output voltage and current for each phase, input units 12, 13, for threshold , values and a processing unit 14 for, based on the measured output voltage and current for each phase and on the threshold values, providing a control signal for varying the inductance of the decoupling inductor.
  • the processing unit 14 comprises means 16 for regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
  • FIG 6 is shown a system where the input units 12 and 13 are adapted to receive threshold values related to symmetry and THD the processing unit 14 is adapted to based on measured values, on third harmonics thresholds and on symmetry thresholds, to provide a control signal for varying the inductance of the decoupling inductor.
  • Figure 7 shows a system according to the invention, where the non-linear circuit elements are variable inductors T4, T5 and T6 comprising a second magnetic core, a main winding H wound around the core and a control winding ST wound around the core.
  • Variable inductors T4, T5 and T6 comprise each a third winding Nd4, Nd5 and Nd6 wound around the second core included in the delta configuration.
  • the figures show three separate cores, one for each circuit element, it is to be understood that the invention comprises use of a single core for the three phases.
  • the separate cores will in this case represent parts of the single core.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Ac-Ac Conversion (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Power Conversion In General (AREA)

Abstract

Device for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of, for each phase, an autotransformer (T1, T2, T3) with a first magnetic core (1, 2, 3), a series winding (Ns1, Ns2, Ns3) and a parallel winding (Npl, Np2, Np3), and a circuit element with a non-linear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said device comprising : one third winding (Nd1, Nd2, Nd3) for each phase, wound around said first magnetic core of the autotransformer, wherein said third windings are connected to each other in a delta configuration. The invention comprises also a device, a method and a control system for reducing harmonics.

Description

BOOSTER
The present invention relates to devices, a method and a system for reduction of harmonics. In particular, the present invention relates to reduction of third harmonics in a device for voltage control and/or voltage stabilisation of a three- phase power supply.
International patent application WO 2004/053615, the contents of which are hereby fully incorporated by reference, describes a system for voltage stabilisation of power supply lines. This system is adapted for use in "insulated terra" (IT) networks, that is in networks isolated from ground. In such a network the most important harmonic components caused by the non-linearity of the inductance components (the zero sequence harmonics) will cancel each other out. This is because they are in phase and represent no difference in potential between the three phases. Since in an IT system all loads are connected in a delta configuration directly between the three phases, no resulting current will be caused by these harmonics.
Use of a system as described in WO 2004/053615 in TN ("terra neutral") networks, however, will lead to significant third harmonic load voltages that will not cancel each other out. Instead, the zero sequence harmonics will add up relative to ground and cause significant currents to ground through the loads, and a corresponding high level of total harmonic distortion (THD).
The European standard EN50160, "Voltage characteristics of electricity supplied by public distribution systems" sets, among other things, a maximum level for THD and harmonics for voltage supplied to consumers.
It is thus an object of the present invention to provide devices, a method and a system for reduction of harmonics in a three phased voltage supply with voltage stabilisation in the form of an autotransformer.
In particular it is an object of the invention to provide devices, a method and a system for reduction of harmonics in a system where harmonics are injected into the core of an autotransformer by a circuit element with non-linear characteristics. In order to achieve this object the invention provides a device for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of, for each phase, an autotransformer with a first magnetic core, a series winding and a parallel winding, and a circuit element with a non-linear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said device comprising: one third winding for each phase, wound around said first magnetic core of the autotransformer, wherein said third windings are connected to each other in a delta configuration.
In one embodiment of the invention, each non-linear circuit element is a variable inductor connected to the autotransformer, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized. This variable inductor and its connection to the autotransformer are described in WO 2004/053615.
The invention is, however, intended to also cover use of other nonlinear devices such as a transformer or other saturable devices, a triac, a thyristor, a rectifier device, or an arcing device.
The nonlinear circuit elements cause harmonic components to be injected into the autotransformer, because of their nonlinear voltage-current characteristics. The injected harmonic components result in undesirable harmonic flux components in the first magnetic cores, and since the loads are all connected to a common ground, harmonic currents will run through the loads to ground.
By connecting a third winding to each autotransformer and connecting these to each other in a delta configuration, a closed circuit is provided. This closed circuit has low impedance for induced 3r harmonic currents, because all such currents will be in phase. Consequently all induced 3rd harmonic currents will circulate in this closed circuit instead of being injected into the load, and hence ampere-winding balance for 3rd harmonic currents is obtained. Other zero sequence harmonics will also be reduced by this method.
For symmetric loads, a current of fundamental frequency will not flow in the delta connection. This follows from the fact that all the induced voltages over the delta connected windings will have a phase difference of 120 degrees, and as long as they are of the same magnitude they will cancel each other out.
If the load is unbalanced, however, the voltages over the three windings will no longer be of the same magnitude, and a current of fundamental frequency will be induced in the delta circuit. According to one embodiment of the invention, this induced current is limited by the connection of a decoupling inductor included in the delta configuration.
The dimensioning of the decoupling inductor will have to be based on a compromise between the wish to counteract load unbalance on the one hand, and the need for reduction of 3rd harmonics on the other. If the decoupling inductor has a high inductance, the level of 3rd harmonic will not be reduced sufficiently; if it is too low, it will not be possible to control the voltages of each phase independently. It is an object of the invention to provide a satisfactory compromise between these requirements, and more specifically to comply with the limits established by international and national standards, such as e.g. EN50160 and other IEC, IEEE or European standards, or national regulations (e.g. the Norwegian "Forskrift om leveringskvalitet i kraftsystemet").
According to one embodiment of the invention the decoupling inductor is variable, and in one variant of this embodiment, the decoupling inductor comprises a magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, such that the inductance of the decoupling inductor is controllable by the current flowing in the control winding.
Use of an autotransformer system for IT grids can result in asymmetric load voltages in certain load situations. This is partly due to the control system consisting of three independent PI controllers, each of them measuring one load voltage (line-line) and controlling one of the three line currents. A load (line-line) voltage may be regarded as a result of two line currents through a load impedance (between two phases), the effective load voltage is then controlled by two independent controllers. This concept can lead to worse operating conditions for the variable inductor with increased THD in addition to unnecessary asymmetric load voltages. By adding a third winding wound around said second core (a winding which is adapted to create a magnetic field with the same direction as the main field) and including these three third windings in the delta circuit the performance of the autotransformer system can be enhanced.
The invention also relates to a method for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of for each phase, an autotransformer with a first magnetic core, a series winding and a parallel winding, and a circuit element with a non-linear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said method comprising the steps of: - providing, for each phase, a third winding wound around the first magnetic core, and
- connecting the third windings to one another in delta configuration.
In an embodiment of the method, the non-linear circuit element is a variable inductor connected to the autotransformer, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized. In another embodiment, it is a transformer, or other saturable devices, or a triac, a thyristor, a rectifier device, a saturable device, or an arcing device. In an embodiment, the method further comprises the step of including a decoupling inductor in the delta configuration, and in a variant of this method, it comprises varying the inductance of the decoupling inductor.
In an embodiment where the decoupling inductor comprises a third magnetic core, a second main winding wound around the core and a second control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, such that the inductance of the decoupling inductor is controllable by the current flowing in the control winding. In other words, the method comprises regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
In an embodiment the method comprises controlling decoupling of the voltages of the three phases from one another by strongly unbalanced loads by varying the inductance of the variable inductor.
In an embodiment, the method comprises reducing third harmonics and other zero sequence harmonics and regulating the level of symmetric output voltages with strongly unbalanced loads by varying the inductance of the variable inductor.
The invention also relates to a device for voltage stabilisation of a three-phase supply, comprising a device according to the invention as described above for reducing harmonics in the delivered voltage resulting from any harmonic component of the magnetic flux in the magnetic core of the autotransformer injected by the non-linear circuit element.
The invention comprises also a regulating system for voltage stabilisation of a three-phase power supply, the regulating system comprising a voltage stabilisation device according to the invention, and comprising measuring units for output voltage and current for each phase, an input unit and a processing unit for, based on the measured output voltage and current for each phase and on the threshold values, varying the inductance of the decoupling inductor.
In an embodiment of the system the decoupling inductor comprises a third magnetic core, a second main winding wound around the core and a second control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, and the processing unit comprises means for regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
In an embodiment of the system the input unit is adapted to receive threshold values for third degree harmonics and the processing unit is adapted to based on measured values and on third degree harmonics thresholds, to vary the decoupling inductor's inductance. In a variant of this embodiment the input unit is adapted to receive threshold values related to symmetry and the processing unit is adapted to based on measured values, on third harmonics thresholds and on symmetry thresholds, to vary the decoupling inductor's inductance.
The invention will now be explained by means of ,an example illustrated in the attached drawings, where:
Figure 1 shows a system for voltage stabilisation of a power supply line in a TN network mainly according to WO 2004/053615.
Figures 2A and 2B show a device according to the invention.
Figures 3 and 4 show third harmonics and third harmonic distortion for three-phase load.
Figures 5 and 6 show a regulating system according to the invention.
Figure 7 shows an embodiment of the invention where each variable inductor comprises a winding included in the delta.
Figure 1 shows a system for voltage stabilisation of a power supply line. The system mainly corresponds with that described in WO 2004/053615, and the respective elements will therefore not be described in detail. Inductors Ll, L2 and L3 are not described in said publication, and neither are they a part of the present invention. Their function is to reduce harmonics and enhance performance with non-symmetric loads. As can be seen in the figure, load Z, generators Gl, G2 and G3, and the primary windings of autotransformers Tl, T2 and T3 are connected in star configuration to a neutral (TN network). This system will show an unacceptably high level of THD.
Figures 2A and 2B show a device 1 for voltage stabilisation of a three-phase supply, comprising, for each phase: - an auto transformer Tl, T2, T3 with a first magnetic core 2, 3, 4, a series winding NsI, Ns2, Ns3 and a parallel winding NpI, Np2, Np3, - a variable inductor T4, T5, T6 connected to the autotransformer Tl, T2, T3 respectively, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized. The figure also shows, for each phase, a third winding NdI, Nd2, Nd3 wound around the first magnetic core 2, 3, 4 respectively, where the third windings associated to each phase NdI, Nd2, Nd3 respectively are connected to one another in delta configuration, and a decoupling inductor Bl connected in series with said delta configuration. The figure also shows parallel inductors Ll, L2 and L3. Figure 2B shows a device according to the invention in a TN network. The third windings NdI, Nd2 and Nd3 are wound about the first magnetic cores 2, 3, 4 respectively such as to create magnetic fields which are mainly parallel to the magnetic fields created by series and parallel windings NsI, Ns2, Ns3 and NpI, Np2 and Np3 respectively.
As mentioned above the decoupling inductor Bl can be variable.
In an embodiment of the invention the decoupling inductor comprises a magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, and the decoupling inductor is adapted to vary the decoupling inductor's inductance by means of the control current. A variable inductor which can be used in the present device is e.g. described in WO 2004/053615.
Figures 3 and 4 show results of experiments on a TN network provided with a device according to the invention. Figure 3 illustrates variation of the third harmonic content in output voltages with three phase symmetric load, with and without the device according to the invention. The line voltage was 400V, the line current was varied between 0 and 80A, and the load was varied between 0 and 30KW. Figure 4 illustrates THD for the same load steps. Typically a value of 5mH (at 50 Hz) for the decoupling inductor was sufficient to ensure performance in accordance with standard EN50160 for a wide range of loads. As already described the dimensioning of this inductor represent a trade off between attenuation of 3 rd harmonics and decoupling of the phases, and the preferred value for the inductor is a design parameter that must be determined based on this and other design criteria. The device was also tested with single phase loads, and even under these circumstances there were no harmful voltage levels between the unloaded phases as long as the decoupling inductor (5mH) was present in the delta configuration.
If a controllable inductor is used, the inductance can be increased in case of open circuited (phase) loads. In this manner the no-load phase can be decoupled from the others and a good voltage control of these phases can still be maintained.
Figures 5 and 6 illustrate a regulating system according to the invention. Said system 5 for voltage stabilisation systems for three-phase power supply comprises a device according to the invention. It also, comprises measuring units 6, 7, 8, 9, 10, 11 for output voltage and current for each phase, input units 12, 13, for threshold , values and a processing unit 14 for, based on the measured output voltage and current for each phase and on the threshold values, providing a control signal for varying the inductance of the decoupling inductor. In an embodiment of the invention where the decoupling inductor comprises a magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, the processing unit 14 comprises means 16 for regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
In figure 6 is shown a system where the input units 12 and 13 are adapted to receive threshold values related to symmetry and THD the processing unit 14 is adapted to based on measured values, on third harmonics thresholds and on symmetry thresholds, to provide a control signal for varying the inductance of the decoupling inductor.
Figure 7 shows a system according to the invention, where the non-linear circuit elements are variable inductors T4, T5 and T6 comprising a second magnetic core, a main winding H wound around the core and a control winding ST wound around the core. Variable inductors T4, T5 and T6 comprise each a third winding Nd4, Nd5 and Nd6 wound around the second core included in the delta configuration.
Although the figures show three separate cores, one for each circuit element, it is to be understood that the invention comprises use of a single core for the three phases. The separate cores will in this case represent parts of the single core.

Claims

1. Device for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of, for each phase, an autotransformer (Tl5 T25 T3) with a first magnetic core (2, 3, 4), a series winding (NsI, Ns2, Ns3) and a parallel winding (NpI, Np2, Np3), and a circuit element with a non-linear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said device comprising: one third winding (NdI5 Nd2, Nd3) for each phase, wound around said first magnetic core of the autotransformer, wherein said third windings are connected to each other in a delta configuration.
2. Device according to claim 1, wherein each of said non-linear circuit elements is a variable inductor (T4, T5, T6) connected to the autotransformer, the variable inductor comprising a second magnetic core, a main winding (H) wound around the core and a control winding (ST) wound around the core axis, where the main and the control winding are adapted to create substantially orthogonal fields when energized.
3. Device according to claim 1, wherein said non-linear circuit element is a transformer, or other saturable device.
4. Device according to claim 1, wherein said non-linear circuit element is chosen from the group of a triac, a thyristor, a rectifier device, and an arcing device.
5. Device according to one of the claims 1 to 4, further comprising a decoupling inductor (Bl) included in said delta configuration.
6. Device according to claim 5, wherein said decoupling inductor is variable.
7. Device according to claim 4, wherein said decoupling inductor comprises a magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, such that the inductance of the decoupling inductor is controllable by the current flowing in the control winding.
8. Device according to claim 2, wherein each of said non-linear circuit elements further comprises a third winding wound around said second magnetic core, each of said third windings being connected to each respective third winding of the autotransformer and thus included in the delta configuration.
9. Method for reducing harmonics in a three phased voltage supply with voltage stabilisation in the form of, for each phase, an autotransformer with a first magnetic core, a series winding and a parallel winding, and a circuit element with a nonlinear current/voltage characteristic causing a harmonic component of the magnetic flux in said magnetic core, said method comprising the steps of:
- providing, for each phase, a third winding wound around the first magnetic core, and
- connecting the third windings to one another in delta configuration.
10. Method according to claim 9, wherein each of said non-linear circuit elements is a variable inductor connected to the autotransformer, the variable inductor comprising a second magnetic core, a main winding wound around the core and a control winding wound around the core axis, where the main and the control winding are adapted to create substantially orthogonal fields when energized.
11. Method according to claim 9, wherein said non-linear circuit element is a transformer, or other saturable device.
12. Method according to claim 9, wherein said non-linear circuit element is chosen from the group of a triac, a thyristor, a rectifier device, a saturable device, and an arcing device.
13. Method according to one of the claims 9 to 12, further comprising the step of including a decoupling inductor in the delta configuration.
14. Method according to claim 13, wherein said decoupling inductor is a variable inductor.
15. Method according to claim 14, wherein said decoupling inductor comprises a third magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, such that the inductance of the decoupling inductor is controllable by the current flowing in the control winding.
16. Method according to claim 14, further comprising the step of controlling decoupling of the voltages of the three phases from one another by varying the inductance of the variable inductor.
17. Device for voltage stabilisation of a three-phase supply, comprising a device according to one of the claims 1 to 8 for reducing harmonics in the delivered voltage resulting from any harmonic component of the magnetic flux in the magnetic core of the autotransformer injected by the non-linear circuit element.
18. Regulating system for voltage stabilisation systems for three-phase power supply including a voltage stabilisation device according to claim 17, comprising measuring units for output voltage and current for each phase, input units for threshold values and a processing unit for, based on the measured output voltage and current for each phase and on the threshold values, varying the inductance of the decoupling inductor.
19.. System according to claim 18, where the decoupling inductor comprises a third magnetic core, a main winding wound around the core and a control winding wound around the core, where the main and the control windings are adapted to create substantially orthogonal fields when energized, and the processing unit comprises means for regulating the current supplied to the control winding to vary the decoupling inductor's inductance.
20. System according to claim 18 or 19, where the input unit is adapted to receive threshold values for third degree harmonics and the processing unit is adapted to based on measured values and on third degree harmonics thresholds, to vary the decoupling inductor's inductance.
21. System according to claim 20, characterised in that the input unit is adapted to receive threshold values related to symmetry and the processing unit is adapted to based on measured values, on third harmonics thresholds and on symmetry thresholds, to vary the decoupling inductor's inductance.
PCT/NO2005/000468 2004-12-23 2005-12-20 Device for reducing harmonics WO2006068495A2 (en)

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WO2009123469A1 (en) * 2008-03-31 2009-10-08 Magtech As Buck boost topology
CN100570982C (en) * 2006-09-01 2009-12-16 戴如宏 High voltage electric-saver
WO2012028839A2 (en) 2010-09-01 2012-03-08 Emsc (Uk) Limited Improved apparatus & method in relation to voltage optimization
EP2482418A1 (en) * 2011-02-01 2012-08-01 Siemens Aktiengesellschaft Active desynchronization of switching converters

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US20020105816A1 (en) * 2000-10-20 2002-08-08 Delta Transformers Of Canada (1999) Ltd. Power center unit for electronic equipment
WO2004053615A1 (en) * 2002-12-12 2004-06-24 Magtech As System for voltage stabilization of power supply lines

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US20020105816A1 (en) * 2000-10-20 2002-08-08 Delta Transformers Of Canada (1999) Ltd. Power center unit for electronic equipment
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CN100570982C (en) * 2006-09-01 2009-12-16 戴如宏 High voltage electric-saver
WO2009123469A1 (en) * 2008-03-31 2009-10-08 Magtech As Buck boost topology
WO2012028839A2 (en) 2010-09-01 2012-03-08 Emsc (Uk) Limited Improved apparatus & method in relation to voltage optimization
EP2482418A1 (en) * 2011-02-01 2012-08-01 Siemens Aktiengesellschaft Active desynchronization of switching converters
US9160170B2 (en) 2011-02-01 2015-10-13 Siemens Aktiengesellschaft Active desynchronization of switching converters

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