WO2014203091A1 - Method and arrangement to actively equalize reference potentials before the grid connection of a photovoltaic installation - Google Patents

Method and arrangement to actively equalize reference potentials before the grid connection of a photovoltaic installation Download PDF

Info

Publication number
WO2014203091A1
WO2014203091A1 PCT/IB2014/061093 IB2014061093W WO2014203091A1 WO 2014203091 A1 WO2014203091 A1 WO 2014203091A1 IB 2014061093 W IB2014061093 W IB 2014061093W WO 2014203091 A1 WO2014203091 A1 WO 2014203091A1
Authority
WO
WIPO (PCT)
Prior art keywords
voltage
power
power converter
installation
equalization means
Prior art date
Application number
PCT/IB2014/061093
Other languages
French (fr)
Inventor
Petar Ljusev
Original Assignee
Sma Solar Technology Ag
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sma Solar Technology Ag filed Critical Sma Solar Technology Ag
Publication of WO2014203091A1 publication Critical patent/WO2014203091A1/en

Links

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
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • 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
    • H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • the present invention reiates to a method and an arrangement for voltag equalization between a photovoltaic (PV) power installation and a power distribution grid, in particular prior to connecting a so!ar power converter of the PV power installation to the grid.
  • the present invention reiates to a method and an arrangement for avoiding ground inrush currents between the PV installation and the power grid whe the solar power converter closes its relays towards the grid.
  • Power generating sources such as renewable energy sources, should he connectahle to associated power distribution grids without generating inrush currents, such as ground inrush currents.
  • inrush currents such as ground inrush currents.
  • output voltage levels of the power generating sources are typically matched and synchronised to the associated grid voltages prior to connecting the power generating sources and the power distribution grid.
  • this method involves measurements of the output voltages and the grid voltages which may be a difficult and costly procedure.
  • Unequalilityage levels of the power generating sources and the power distribution grid voltages can be result of a minor ground isolation failure of th power generating source, but which still satisfy the safety conditions for connecting to the grid, It may he seen as an object of embodiments of the present invention to provide a voltage equalisation method in order to avoid ground inrush currents when a PV installation is connected to an associated power distribution grid.
  • the above-mentioned object is complied with by providing, in a first aspect, a method for connecting a PV power installation to a power distribution grid in a manner so as to avoid ground inrush currents at the moment when a power converter's relays are closed, the method comprising the steps of - activating a voltage equalization means positioned between at !east one output phase and an earthed point of a power converter of the PV power Installation,
  • the internal voltage levels of the powe converter may be an interna! neutral of said power inverter which is matched to a neutral of the power distribution grid.
  • the PV power installation may be connected to the power distribution grid without inducing ground inrush currents.
  • the method of the present invention aims at providing a smooth connection of the PV power installation to a power grid connectable thereto.
  • smooth is meant that essentia!y no ground inrush currents are generated at the time of connection .
  • the smooth connection is accomplished by rnatching the internal voltage ievels of the powe converter of the PV power installation with the grid voltage while noting that both voltages are referenced to earth.
  • both the voltage applied across the voltage equalization means and the voltage of the power distribution grid are both referenced to earth.
  • Activation of the voltage equalization means should be understood broadly. Thus, activation may be provided by various means, such as by using a controiiable switch.
  • the earthed point of the power converte may for example be a point on the chassis of said power converter.
  • the power converter switches may involve transistors, such as insulated-gate bipoiar transistors (IGBTs) or metai-oxide-semieonductor field-effect transistors (MOSFETs),
  • IGBTs insulated-gate bipoiar transistors
  • MOSFETs metai-oxide-semieonductor field-effect transistors
  • the power converter may generally be operated in the following two modes of operations ; 1. as a DC/DC power converter prior to connecting the PV instaliation to the power grid, and
  • the power converter switches are controlled in order to control the ievei of the mousseage applied across the voltage equaSization means.
  • the value of the applied voltage is based on measured interna! converter voltages, in particular how these salage ievels match to the voltages of the power distribution grid.
  • the power converter switches may by controlled using a duty cycie control scheme, Even though the power converter is intended to be operated as a DC/ AC converter during norma! operation the mousseage applied across the dishage equalization means may be a DC voltage. Both negative and positive DC voltages may be applied across the voltage
  • the power converter may be operated as a DC/AC converter when the PV power installation is fully connected to the power distribution grid, and power is transferred from the PV installation to the power grid.
  • the output recreationalage and the output frequency of the DC/AC converter, and thereby the PV instaSiation, may he matched to a nornina!dronage Ievei of the power grid.
  • a grid transformer may be inserted between the P installation and the power grid in order to match the respective sculptureage ievels.
  • a grid transformer may transform the sculptureage of the PV instaliation to a higher Dahlage !eve!.
  • the voltage equalization means may comprise a leakage resistor and a controllable switch connected in series. Activation of the voltage equalization means may be provided by the dosing the switch, whereas de-activation of the lakeage equalization means may be provided by opening the switch.
  • the controllable switch may be a suitable transistor or a mechanical relay.
  • the sculptureage equalization means may he provided for each output phase of the power converter of the PV power instaliation.
  • the present invention relates to an arrangement for connecting a PV power installation to a power distribution grid in a manner so as to avoid ground inrush currents, the arrangement comprising - voltage equalization means positioned between at least one output phase and an earthed point of a power converter of the PV power installation, said power converter comprising a first and a second set of power converter switches.
  • - control means for controlling the respective first and second sets of power converter switches in orde to apply a voltage across the voltage equalization means
  • controllable circuit breaker arrangement for connecting and disconnecting the PV power installation to the powe distribution grid.
  • the arrangement of the second aspect is adapted to carry out the method of the first aspect.
  • the power converter may be configured as explained in relation to the method of the first aspect.
  • the voltage equalization means may comprise a leakage resistor and a controllable switch, such as a transistor or relay, connected in series. Appropriate control means for controlling the controllable switch may be provided as weii,
  • Voltage equalization means may be provided for a single or a plurality of output phases of the power converter. In fact each output phase of the power converter of the PV power installation may be connected to a voltage equalization means.
  • the first set of power converter switches such as IGBTs or MOSFETs, may be adapted to provide a positive DC voltag across the voltage equalization means, whereas the second set of power converter switches, such as IGBTs or MQSFETs, may be adapted to provide a negative DC voltage across the lakeage equalization means.
  • the control means may be adapted to control the power converter switches applying a duty cycle control scheme.
  • the present invention relates to a PV power instailation comprising an arrangement according to the second aspect.
  • the PV power installation may be an installation for domestic purposes, for example a 2-8 kVV installation, or it may be a !arger industrial-like installation.
  • Fig. 1 shows a simple PV power installation. While the invention is susceptible to various modifications and alternative forms, a specific embodiment has been shown by way of an example in the drawing and wiil be described in detail herein. It shouid be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover ail modifications, equivalents, and alternatives failing within the spirit and scope of the invention as defined by the appended claims.
  • the present invention relates to a method and an arrangement for smooth connection of a PV power installation to an associated power distribution grid.
  • the present invention aims at avoiding damaging ground inrush currents and tripping of Residua! Current Devices (RCDs) when the PV power installation is connected to the power distribution grid.
  • the smooth connection involving essentia!ly no ground inrush currents is provided via voltage equalization.
  • the installation comprises a PV array 101 coupled to a power converter 102 which during normal operation of the PV installation Is operated as a DC/ AC power converter.
  • the DC/ AC power converter may be a single phase, as depicted in Fig, 1, or a multiphase power converter, such as a three phase converter,
  • AC power provided by the power converter 102 is provided to a power distributio grid 108 via a LCL filter 103 and a set of controliabie reiays 107.
  • the controliabie relays 10? are adapted to connect and disconnect the PV power installation from the power grid 108.
  • the LCL filter is used for smoothing the power converter output, removing the switching ripple and higher order harmonics being a result of the switched operation.
  • the LCL filter 103 may form an integral part of the converter 102.
  • a resistor-based vo!tage equalization arrangement/means is provided between at least one phase of the power converter 102 and earth 106.
  • the resistor-based Kunststoffage equalization arrangement comprises a resistor 104 and a controllable switch 105 for activation and deactivation of the arrangement.
  • the resistance of the resistor 104 matches the minimum ailowed isolation resistance of the installation.
  • a 1 kv instaiiation is ailowed to operate with a minimum isolation resistance of 33 kti.
  • the installation Prior to connecting the PV instaiiation to the power grid, the installation is typically operated in the following manner: Electrical power in the form of DC power is generated by the PV array 101 and delivered to the power converter 102 which may be either a single or a multiple phase power converter.
  • the power converter 102 is operated as a DC/AC power converter in order to be capable of delivering AC power to the power grid 108.
  • a grid transformer ⁇ not shown) may be inserted between the power converter 102 and the power grid 108 in order to ensure match of voltages.
  • the internai voltage !eveis of the powe converter 102 involve an internai neutral of said power inverter 102,
  • the interna! neutral is matched to a neutral of th power grid 108,
  • the PV installation is con nected to the power grid 108 without inducing ground inrush currents.
  • the PV installation Prior to connecting the PV installation to the power grid, i.e. when the controllable relays 107 are open, the PV installation is floating and the installation's potential with respect to earth is determined by the resistances ⁇ to earth) of the PV array 101 and power converter 102. According to the safety standard for power converters in PV installations, IEC62109-2, it will be allowed to operate PV installations with a minimum PV isolation resistance of 33ki2 ⁇ ⁇ 1000V/30mA),
  • An isolation error can be located either asymmetrically (in worse case on DC+ or DC-) or symmetrically on PV/2..
  • Such isolation erro may pull the potential of an internai midpoint of the power converter 102 to eithe side.
  • it is required to be able to pull the potential of the PV installation in either direction with as much resistance as the isolation error, i. e. minimum 33 kCt, and the same voltages. This requirement may be realized by mounting a 33 kft leakage resistor 104 at the output of one of the phases of the power converter 102 and connecting the othe side to the chassis, i.e.
  • the leakage resistor 104 is energized (with the controllable switch 105 being in a closed position) by the power converter 102 until the potential of art internal midpoint of the power converter reaches 0 V. At this stage the controllable switch 105 is opened and the PV installation is then connected to the power grid by closing the controllable reiays 107.

Abstract

The present invention relates to a method for connecting a PV power installation (101) to a power distribution grid (108) in a manner so as to avoid ground inrush currents, the method comprising the steps of activating a voltage equalization means (104-105) positioned between at least one output phase and an earthed point (106) of a power converter of the PV power installation, applying a voltage across the voltage equalization means, controlling the level of the applied voltage in order to match internal converter voltage levels to voltage levels of the power distribution grid at a given time, de¬ activating the voltage equalization means when the internal converter voltage levels match the voltage levels of the power distribution grid, and connecting the PV power installation to the power distribution grid. The invention further relates to an associated arrangement.

Description

METHOD AND ARRANGEMENT TO ACTIVELY EQUALIZE REFERENCE POTENTIALS BEFORE THE GRID CONNECTION OF A PHOTOVOLTAIC INSTALLATION
FIELD OF THE INVENTION
The present invention reiates to a method and an arrangement for voltag equalization between a photovoltaic (PV) power installation and a power distribution grid, in particular prior to connecting a so!ar power converter of the PV power installation to the grid. In parttcuiar, the present invention reiates to a method and an arrangement for avoiding ground inrush currents between the PV installation and the power grid whe the solar power converter closes its relays towards the grid.
BACKGROUND OF THE INVENTION Power generating sources., such as renewable energy sources, should he connectahle to associated power distribution grids without generating inrush currents, such as ground inrush currents. In order to avoid generation of inrush currents output voltage levels of the power generating sources are typically matched and synchronised to the associated grid voltages prior to connecting the power generating sources and the power distribution grid. However,, this method involves measurements of the output voltages and the grid voltages which may be a difficult and costly procedure. Unequal voitage levels of the power generating sources and the power distribution grid voltages can be result of a minor ground isolation failure of th power generating source, but which still satisfy the safety conditions for connecting to the grid, It may he seen as an object of embodiments of the present invention to provide a voltage equalisation method in order to avoid ground inrush currents when a PV installation is connected to an associated power distribution grid.
It may be seen as a further object of embodiments of the present invention to provide a method for connecting a PV installation to an associated power distribution grid without measuring the output voltages of the PV installation and the grid voltages.
DESCRIPTION OF THE INVENTION
The above-mentioned object is complied with by providing, in a first aspect, a method for connecting a PV power installation to a power distribution grid in a manner so as to avoid ground inrush currents at the moment when a power converter's relays are closed, the method comprising the steps of - activating a voltage equalization means positioned between at !east one output phase and an earthed point of a power converter of the PV power Installation,
- controlling a first and/or a second set of power converter switches in order to apply a voltage across the voltage equalization means, - controlling the level of the applied voltage in order to match internal voltage ievels of the power converter to voltage levels of the power distribution grid at a given time.,
- de-activating the voltage equalization means when the internal voltage levels of the power converter match the voltage ievels of the power distribution grid, and
- connecting the PV power installation to the powe distribution grid. The internal voltage levels of the powe converter may be an interna! neutral of said power inverter which is matched to a neutral of the power distribution grid. When a match is provided between the interna! neutral of the power converter and the neutral of the powe distributing grid the PV power installation may be connected to the power distribution grid without inducing ground inrush currents. Thus, the method of the present invention aims at providing a smooth connection of the PV power installation to a power grid connectable thereto. By smooth is meant that essentia!!y no ground inrush currents are generated at the time of connection . The smooth connection is accomplished by rnatching the internal voltage ievels of the powe converter of the PV power installation with the grid voltage while noting that both voltages are referenced to earth. Thus, both the voltage applied across the voltage equalization means and the voltage of the power distribution grid are both referenced to earth.
Activation of the voltage equalization means should be understood broadly. Thus, activation may be provided by various means, such as by using a controiiable switch. The earthed point of the power converte may for example be a point on the chassis of said power converter. The power converter switches may involve transistors, such as insulated-gate bipoiar transistors (IGBTs) or metai-oxide-semieonductor field-effect transistors (MOSFETs), In the case where the voltage equalization means does not interfere with the normal operation of the power converter due to e.g. having high impedance without any functional and safety concerns, the voltage equalization means can be continuously connected without any arrangements for activation and deactivation.
The power converter may generally be operated in the following two modes of operations ; 1. as a DC/DC power converter prior to connecting the PV instaliation to the power grid, and
2. as a DC/ AC power converter when the PV instaSiation is connected to the power grid, and power is to be delivered thereto.
Thus, prior to connecting the PV installation to the power grid the power converter switches are controlled in order to control the ievei of the voitage applied across the voltage equaSization means. The value of the applied voltage is based on measured interna! converter voltages, in particular how these voitage ievels match to the voltages of the power distribution grid. The power converter switches may by controlled using a duty cycie control scheme, Even though the power converter is intended to be operated as a DC/ AC converter during norma! operation the voitage applied across the voitage equalization means may be a DC voltage. Both negative and positive DC voltages may be applied across the voltage
equalization means.
As stated above the power converter may be operated as a DC/AC converter when the PV power installation is fully connected to the power distribution grid, and power is transferred from the PV installation to the power grid. The output voitage and the output frequency of the DC/AC converter, and thereby the PV instaSiation, may he matched to a nornina! voitage Ievei of the power grid. Alternatively, a grid transformer may be inserted between the P installation and the power grid in order to match the respective voitage ievels. For example, a grid transformer may transform the voitage of the PV instaliation to a higher voitage !eve!.
The voltage equalization means may comprise a leakage resistor and a controllable switch connected in series. Activation of the voltage equalization means may be provided by the dosing the switch, whereas de-activation of the voitage equalization means may be provided by opening the switch. The controllable switch may be a suitable transistor or a mechanical relay. The voitage equalization means may he provided for each output phase of the power converter of the PV power instaliation. i n a second aspect the present invention relates to an arrangement for connecting a PV power installation to a power distribution grid in a manner so as to avoid ground inrush currents, the arrangement comprising - voltage equalization means positioned between at least one output phase and an earthed point of a power converter of the PV power installation, said power converter comprising a first and a second set of power converter switches. - control means for controlling the respective first and second sets of power converter switches in orde to apply a voltage across the voltage equalization means,
- determining means for determining when interna! converter voltage levels, when referenced to earth, match voltage levels of the power distribution grid, when referenced to earth, and
- a controllable circuit breaker arrangement for connecting and disconnecting the PV power installation to the powe distribution grid.
Generally, the arrangement of the second aspect is adapted to carry out the method of the first aspect. Thus, the power converter may be configured as explained in relation to the method of the first aspect. Moreover, the voltage equalization means may comprise a leakage resistor and a controllable switch, such as a transistor or relay, connected in series. Appropriate control means for controlling the controllable switch may be provided as weii,
Voltage equalization means ma be provided for a single or a plurality of output phases of the power converter. In fact each output phase of the power converter of the PV power installation may be connected to a voltage equalization means.
The first set of power converter switches, such as IGBTs or MOSFETs, may be adapted to provide a positive DC voltag across the voltage equalization means, whereas the second set of power converter switches, such as IGBTs or MQSFETs, may be adapted to provide a negative DC voltage across the voitage equalization means. The control means may be adapted to control the power converter switches applying a duty cycle control scheme.
In a third aspect the present invention relates to a PV power instailation comprising an arrangement according to the second aspect. The PV power installation may be an installation for domestic purposes, for example a 2-8 kVV installation, or it may be a !arger industrial-like installation. BRIEF DESCRIPTION OF THE DRAWING
The present invention will now be described in further details with reference to the accompanying figures, where
Fig. 1 shows a simple PV power installation. While the invention is susceptible to various modifications and alternative forms, a specific embodiment has been shown by way of an example in the drawing and wiil be described in detail herein. It shouid be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover ail modifications, equivalents, and alternatives failing within the spirit and scope of the invention as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
In its most general aspect the present invention relates to a method and an arrangement for smooth connection of a PV power installation to an associated power distribution grid. Thus, the present invention aims at avoiding damaging ground inrush currents and tripping of Residua! Current Devices (RCDs) when the PV power installation is connected to the power distribution grid. The smooth connection involving essentia!ly no ground inrush currents is provided via voltage equalization.
Referring now to Fig, i a simple PV power installation 100 is depicted. As seen, the installation comprises a PV array 101 coupled to a power converter 102 which during normal operation of the PV installation Is operated as a DC/ AC power converter. The DC/ AC power converter may be a single phase, as depicted in Fig, 1, or a multiphase power converter, such as a three phase converter,
AC power provided by the power converter 102 is provided to a power distributio grid 108 via a LCL filter 103 and a set of controliabie reiays 107. The controliabie relays 10? are adapted to connect and disconnect the PV power installation from the power grid 108. The LCL filter is used for smoothing the power converter output, removing the switching ripple and higher order harmonics being a result of the switched operation. The LCL filter 103 may form an integral part of the converter 102. Moreover, a resistor-based vo!tage equalization arrangement/means is provided between at least one phase of the power converter 102 and earth 106. In the shown example the resistor-based voitage equalization arrangement comprises a resistor 104 and a controllable switch 105 for activation and deactivation of the arrangement. Typically, the resistance of the resistor 104 matches the minimum ailowed isolation resistance of the installation. As an example, a 1 kv instaiiation is ailowed to operate with a minimum isolation resistance of 33 kti.
Prior to connecting the PV instaiiation to the power grid, the installation is typically operated in the following manner: Electrical power in the form of DC power is generated by the PV array 101 and delivered to the power converter 102 which may be either a single or a multiple phase power converter.
During normal operation, i.e. when the PV installation 100 is connected to the power grid 108, the power converter 102 is operated as a DC/AC power converter in order to be capable of delivering AC power to the power grid 108, As previously mentioned internai voltage levels of the power converter 102 is matched to the voltage level of the power grid 108, A grid transformer {not shown) may be inserted between the power converter 102 and the power grid 108 in order to ensure match of voltages.
The internai voltage !eveis of the powe converter 102 involve an internai neutral of said power inverter 102, The interna! neutral is matched to a neutral of th power grid 108, When a match Is provided between the internal neutral of the power converter 102 and the neutra! of the power grid 108 the PV installation is con nected to the power grid 108 without inducing ground inrush currents. Prior to connecting the PV installation to the power grid, i.e. when the controllable relays 107 are open, the PV installation is floating and the installation's potential with respect to earth is determined by the resistances {to earth) of the PV array 101 and power converter 102. According to the safety standard for power converters in PV installations, IEC62109-2, it will be allowed to operate PV installations with a minimum PV isolation resistance of 33ki2 { ~ 1000V/30mA),
An isolation error can be located either asymmetrically (in worse case on DC+ or DC-) or symmetrically on PV/2.. Such isolation erro may pull the potential of an internai midpoint of the power converter 102 to eithe side. In order to equalize the potentials on both sides of the controllable relays 107 it is required to be able to pull the potential of the PV installation in either direction with as much resistance as the isolation error, i. e. minimum 33 kCt, and the same voltages. This requirement may be realized by mounting a 33 kft leakage resistor 104 at the output of one of the phases of the power converter 102 and connecting the othe side to the chassis, i.e. an earth connection 106, via a controllable switch 105, With the controllable switch 105 being in a closed position and operating the upper (DC -;- side) or the lower (DC- side) switches in the corresponding power converter phase will apply half of a DC- bus voltage across the leakage resisto 104 and the controllable switch 105, This will pu ll the power converter potential in the opposite direction compared to the isolation error.
The leakage resistor 104 is energized (with the controllable switch 105 being in a closed position) by the power converter 102 until the potential of art internal midpoint of the power converter reaches 0 V. At this stage the controllable switch 105 is opened and the PV installation is then connected to the power grid by closing the controllable reiays 107.

Claims

1. A method for connecting a photovoltaic power installation to a power distribution grid in a manner so as to avoid ground inrush currents, the method comprising the steps of
- activating a voitage equalization means positioned between at feast one output phase and an earthed point of a power converter of the photovoltaic power installation,
- controlling a first and/or a second set of power converter switches in order to apply a voltage across the voitage equalization means,
- controlling the level of the applied voltage in order to match interna! voltage levels of the power converter to voltage levels of the power distribution grid at a given time, - de-activating the voltage equalization means when the internal voltage levels of the power converter matches the voitage levels of the power distribution grid, and
- connecting the photovoltaic power installation to the power distribution grid,
2. A method according to claim 1, wherein the voltage applied across the voltage equalization means and the voitage level of the power distribution grid are both referenced to earth.
3, A method according to claim 1 or 2, wherein the voitage applied across the voitage equalization means is a DC voltage, such as a positive or a negative DC voitage.
4. A method according to any of claims 1-3, wherein the first or the second set of power converter switches comprise IGBTs or MOSFETs.
5, A method according to any of claims 1-4, wherein the first or the second set of power converter switches are controlled via duty cycle control.
6, A method according to any of claims i-S, wherein the power converter is operated as a DC/AC converter when the photovoltaic power installation is connected to the power distribution grid .
7. A method according to any of claims 1-6, wherein the voitage equalization means comprises a leakage resistor and a controllable switch connected in series.
8. A method according to any of the preceding claims, wherein voltage equalization means are provided for each output phase of the power converter of the photovoltaic power installation.
9. An arrangement for connecting a photovoltaic power installation to a power distribution grid in a manner so as to avoid ground inrush currents, the arrangement comprising
- voltage equalisation means positioned between at leas one output phase and an earthed point of a power converter of the photovoltaic power installation, said power converter comprising a first and a second set of power converter switches,
- control means for controlling the respective first and second sets of power converter switches in order to apply a voltage across the voltage equalization means,
- determining means for determining when interna! voltage !eveis of the power converter, when referenced to earth, matches voltage levels of the power distribution grid, when referenced to earth, and
- a controllable circuit breaker arrangement for connecting and disconnecting th photovoltaic power installation to the powe distribution grid,
10. An arrangement according to claim 9, wherein the voltage equalization means comprises a leakage resistor and a controllabl switch connected in series.
11. An arrangement according to claim 9 or 10, wherein voltage equalization means are provided for each output phase of the power converter of the photovoltaic power installation,
12, An arrangement according to any of claims 9- 11, wherein the first set of power converter switches is adapted to provide a positive DC voltage across the voltage equalization means,
13. An arrangement according to any of claims 9-12, wherein the second set of power converter switches is adapted to provide a negative DC voltage across the voltage equalization means,
14. An arrangement according to any of claims 9-13, wherein the control means is adapted to control the power converter switches applying a duty cycle control scheme.
15. A photovoltaic power installation comprising an arrangement according to any of claims
PCT/IB2014/061093 2013-06-18 2014-04-30 Method and arrangement to actively equalize reference potentials before the grid connection of a photovoltaic installation WO2014203091A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DK201300368 2013-06-18
DKPA201300368 2013-06-18

Publications (1)

Publication Number Publication Date
WO2014203091A1 true WO2014203091A1 (en) 2014-12-24

Family

ID=50884964

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2014/061093 WO2014203091A1 (en) 2013-06-18 2014-04-30 Method and arrangement to actively equalize reference potentials before the grid connection of a photovoltaic installation

Country Status (1)

Country Link
WO (1) WO2014203091A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2018538776A (en) * 2015-12-22 2018-12-27 エスエムエイ ソーラー テクノロジー アクティエンゲゼルシャフトＳＭＡ Ｓｏｌａｒ Ｔｅｃｈｎｏｌｏｇｙ ＡＧ Inverter with system breakpoint and insulation resistance measurement, and method for measuring insulation resistance
WO2020099263A1 (en) * 2018-11-12 2020-05-22 Kaco New Energy Gmbh Method for connecting a photovoltaic (pv) inverter to a three-phase network, and pv inverter
WO2024017740A3 (en) * 2022-07-22 2024-03-21 Sma Solar Technology Ag Bridge circuit and energy conversion system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1672776A1 (en) * 2004-12-20 2006-06-21 Sanyo Electric Co. Ltd Interconnected generator system
US20130121029A1 (en) * 2011-11-10 2013-05-16 Sma Solar Technology Ag Connecting an Inverter in a Solar Power Plant with Shifted Potential Center Point
WO2013080878A1 (en) * 2011-11-29 2013-06-06 三洋電機株式会社 Grid connection device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1672776A1 (en) * 2004-12-20 2006-06-21 Sanyo Electric Co. Ltd Interconnected generator system
US20130121029A1 (en) * 2011-11-10 2013-05-16 Sma Solar Technology Ag Connecting an Inverter in a Solar Power Plant with Shifted Potential Center Point
WO2013080878A1 (en) * 2011-11-29 2013-06-06 三洋電機株式会社 Grid connection device

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2018538776A (en) * 2015-12-22 2018-12-27 エスエムエイ ソーラー テクノロジー アクティエンゲゼルシャフトＳＭＡ Ｓｏｌａｒ Ｔｅｃｈｎｏｌｏｇｙ ＡＧ Inverter with system breakpoint and insulation resistance measurement, and method for measuring insulation resistance
WO2020099263A1 (en) * 2018-11-12 2020-05-22 Kaco New Energy Gmbh Method for connecting a photovoltaic (pv) inverter to a three-phase network, and pv inverter
WO2024017740A3 (en) * 2022-07-22 2024-03-21 Sma Solar Technology Ag Bridge circuit and energy conversion system

Similar Documents

Publication Publication Date Title
US10523132B2 (en) Start-up of HVDC converters
US8300435B2 (en) Transmission system and a method for control thereof
US9806618B2 (en) Power converting device and power conditioner using the same
CN110048626B (en) Inverter alternating current closing common-mode impact current suppression method and application device thereof
CN105874703B (en) Inverter with soft switching and method
EP3103189A1 (en) Multilevel inverter device and operating method
US20160146192A1 (en) Wind turbine power conversion system
US20200158085A1 (en) Power converter for full conversion wind turbine systems
US9859808B2 (en) Power converter topology for use in an energy storage system
US20180241321A1 (en) Voltage source converter and control thereof
WO2014203091A1 (en) Method and arrangement to actively equalize reference potentials before the grid connection of a photovoltaic installation
US11770005B2 (en) Fault handling
Zhou et al. Neutral-point-clamped circuits of single-phase PV inverters: Generalized principle and implementation
US9647570B2 (en) Photovoltaic system and method of operation
WO2015172825A1 (en) Ac fault handling arrangement
US20180191280A1 (en) Power Converter for Doubly Fed Induction Generator Wind Turbine Systems
Chen et al. Stacked modular isolated dynamic current source converters for medium voltage applications
Changizian et al. A novel control method for restraining starting-up overcurrent in VSC-HVDC System
Yun et al. High-voltage input power supply for modular multi-level converter
US10411473B2 (en) Power converter for energy systems
Shu et al. Design and Adaptive Control of Matrix Transformer Based Indirect Converter for Large-Capacity Circuit Breaker Testing Application
Li et al. Active virtual ground: Single phase grid-connected voltage source inverter topology
Sagayaraj et al. Performance Analysis of Quazi Z-source inverter Fed Induction Motor under Semiconductor Failure Condition
JP2020089163A (en) Power conversion device
Kim Technical Trends of VSC HVDC

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14728328

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14728328

Country of ref document: EP

Kind code of ref document: A1