Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
  • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
  • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
  • H02H7/122—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters
  • H02H7/1222—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for inverters, i.e. dc/ac converters responsive to abnormalities in the input circuit, e.g. transients in the DC input
• • 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

Definitions

• the invention relates to an input-side protection circuit for a DC link of an inverter against overvoltages, wherein the protection circuit has a DC link upstream and bridgeable by means of a controllable mechanical switching means ballast for voltage limiting the DC link.
• the mechanical switching means can be controlled in such a way that it opens in the feed-in mode of the inverter at an intermediate circuit voltage greater than a predefined voltage limit value.
• the invention relates to an inverter having an input-side intermediate circuit for connection to a regenerative DC voltage source, with an output-side power unit for feeding into an electrical network and with such a controllable input-side protection circuit.
• Regenerative DC sources may be e.g. Be solar modules or a solar panel with a variety of such solar modules. They can be fuel cells or generators of wind turbines or biogas plants.
• the feed can, for example, in a 1-phase
• an electric current generated, for example, by photovoltaic means can also be supplied to a plurality of inverters, which then convert the supplied direct voltage into a mains voltage.
• the DC voltage generated, for example, by a solar field is dependent on the current solar radiation and in particular on its electrical load. At idle, this field or output voltage of the solar field reaches its maximum. This voltage is also referred to as no-load voltage. Under load, ie when fed into the electrical network via the inverter, this voltage drops.
• the inverter has a control unit which controls electronic semiconductor components in the power section of the inverter in such a way that the power fed into the electrical grid is maximum.
• the control unit typically executes a so-called tracking program in order to continuously search for the likewise fluctuating maximum power point (MPP for the maximum power point).
• MPP fluctuating maximum power point
• a solar module or a solar field as a DC voltage source has an electrical characteristic under load, which comes closer to that of a current source. This means that the generated current is essentially independent of the field or output voltage of the solar module or solar field, assuming the same solar radiation, in which case the voltage applied to the solar module or the solar field idle voltage at a relatively low load rapidly decreases (see FIG 2). However, the open-circuit voltage may exceed the permissible operating voltage of the solar inverter in strong sunlight.
• an input-side protective circuit In order to avoid inadmissibly high voltages at the input of the intermediate circuit, an input-side protective circuit is known from the patent Abstract of Japan for JP 11312022 A. It comprises a series connection of two resistors as a voltage divider and three controllable mechanical switching means. If a field voltage applied on the input side is smaller than a predefined voltage limit value, then the mechanical switching means are controlled in such a way that the field voltage is applied directly to the DC link.
• the mechanical switching means may be relays or contactors. If the intermediate circuit voltage exceeds the predetermined voltage limit value, then the switching means are activated in such a way that the field voltage at the series connection and the center tap with a voltage-divided, reduced voltage value are applied to the intermediate circuit.
• the object of the invention is achieved with the features of patent claim 1.
• Advantageous embodiments are given in the dependent claims 2 to 7.
• a suitable inverter is called.
• the protective circuit has an electronic voltage limiter connected downstream of the series-connected element and connected in parallel with the intermediate circuit.
• the electronic voltage limiter is in
• Switching time of the mechanical switching means on the voltage limiter dropping electrical power is several orders of magnitude above the falling on the resistors of the series connection electrical power.
• the resistors provided for limiting the voltage are typically designed thermally for the indefinite case.
• the electronic voltage limiter has a voltage detection unit for detecting the DC link voltage, a comparator for comparing a currently detected voltage measurement value with a reference voltage value corresponding to the voltage limit value, a controllable electronic switching element connected downstream of the comparator and a series circuit connected in parallel to the intermediate circuit from the load side Part of the electronic switching element and a limiting resistor. This is one of the control of the Inverter independent operation of the protection circuit according to the invention possible.
• the comparator is designed as a chopper for controlled clocked control of the electronic switching element.
• the particular advantage is that only a comparatively low power loss drops at the switching element, while the by far largest part of the electrical power at the ballast for voltage limitation drops.
• the latter is preferably a resistor, e.g. a power resistor.
• the electronic switching element is usually a transistor.
• the chopper can have a pulse width modulator for controlled clocked driving of the electronic switching element with a constant switching frequency.
• the electronic voltage limiter has a structurally particularly simple structure.
• Switching means controlled such that it is open in the off state of the inverter. As a result, the input-side voltage limitation is active even when the inverter is switched off.
• the object of the invention is further achieved by an inverter with a protection circuit according to the invention.
• all components for the protection circuit are integrated on the circuit carrier of the controller for the inverter.
• the inverter according to the invention is preferably a solar inverter for input-side connection to a solar module or to a solar field.
• the inverter may alternatively be connected to a fuel cell.
• FIG. 1 shows by way of example an inverter with an input-side protection circuit according to the prior art for protecting the intermediate circuit of the inverter from overvoltages
• FIG. 2 shows an example of a current / voltage characteristic of a solar module as an example of a regenerative DC voltage source
• FIG. 3 shows by way of example an inverter with a protective circuit according to the invention according to a first embodiment
• FIG. 4 shows by way of example a further inverter with a protective circuit according to the invention according to a second embodiment.
• reference numeral 1 denotes a known inverter.
• On the input side it has a voltage intermediate circuit 2, consisting of a DC link capacitor 8 and a DC link resistor RS connected in parallel thereto.
• the latter can be, for example, a discrete component.
• the DC link resistor RS can also be a discharge resistor for contact protection.
• the intermediate circuit 2 is provided for connection to a regenerative DC voltage source 3, for example to a solar field.
• the intermediate circuit 2 is the output side, a power unit 4 for feeding into an electrical network N downstream.
• the power unit 4 converts an applied intermediate circuit DC voltage uZK into an output-side AC voltage.
• the inverter 1 shown provides a three-phase mains voltage at three output terminals 11.
• the intermediate circuit 2 is preceded by an input-side protection circuit 5 'for protection against overvoltages. It has, for example, a controllable mechanical switching means 7, which can bridge a resistor as a ballast element RV for limiting the voltage of the intermediate circuit 2.
• the mechanical switching means 7 is controlled in such a way that, in the feed-in mode of the inverter 1, it opens larger than a predetermined voltage limit value at an intermediate circuit voltage uZK.
• this mechanical switching means 7 is an electrically controllable relay or
• the dashed line 15 symbolizes the controllability of the switching means 7, such as, for example, FIG. via an electronic control unit of the inverter 1 or via an overvoltage or undervoltage relay.
• UF denotes a field or output voltage of the solar field 3, which is applied to input terminals 10 of the inverter 1.
• I denotes a current which flows, inter alia, through the shown series resistor RV and causes a voltage drop uR at this point.
• the intermediate circuit voltage uZK is reduced by this voltage uR in comparison to the field voltage uF.
• the resistance value of the series resistor RV is dimensioned such that a sufficient voltage drop is achieved at a maximum output voltage of the regenerative DC voltage source.
• the mechanical switching means 7 can also be controlled in such a way that, in the feed-in or regenerative mode of operation of the inverter 1, it closes below a predefinable voltage limit value at an intermediate circuit voltage uZK. This is the case when the DC link voltage uZK has dropped by the load of the DC link 2 so far that a safe operation of the power unit 4 without a risk of destruction of the semiconductor switch is possible.
• the predefinable voltage limit can be set to a voltage limit of 500V, for example, if the maximum expected output voltage of the DC voltage Source 3, such as that of a solar field 3, is about 1000V.
• FIG. 2 shows an example of a current / voltage characteristic 20 of a solar module as an example of a regenerative DC voltage source.
• the electric current i generated by the solar module is almost constant over wide field voltages ⁇ F.
• any point on the characteristic curve 20 can be traversed by the power section of the inverter.
• the maximum field voltage UL at the solar module is then applied, while in the case of a short circuit of the power module, a short-circuit current IK occurs.
• MPP denotes a maximum power point of the characteristic curve 20 at which a maximum mains feedback is possible. With UP the associated field voltage is designated.
• the field voltage uF decreases relatively quickly at a load of the solar module.
• a comparatively low load already suffices to allow the field voltage uF to drop from the maximum open-circuit voltage UL to a predefinable exemplary limit voltage UG, below which safe operation of semiconductor switches is possible.
• the protection circuit 5 has an electronic voltage limiter 6 which is connected downstream of the ballast RV connected as a resistor and connected in parallel with the intermediate circuit 2.
• the latter is preferably thermally designed only for receiving the falling down to the opening of the mechanical switching means 7 on the voltage limiter 6 electrical input power, that is, for a typical period of about 100 to 200 ms.
• the time to be thermally bridged accordingly the switching time for opening the mechanical switching means 7 are also lower, such as at about 50 ms, or above, such as 500 ms.
• the electronic voltage limiter 6 has a voltage detection unit 61 for detecting the intermediate circuit voltage uZK and a comparator 62 or comparator for comparing a currently detected voltage measurement value UM with a comparison voltage value UV corresponding to the voltage limit value UG. Furthermore, the voltage limiter 6 has a controllable electronic switching element 64 connected downstream of the comparator 62 and a series circuit connected in parallel to the intermediate circuit 2 from the load-side part of the electronic switching element 64 in the form of a transistor and a limiting resistor RB.
• Reference numeral 63 denotes a reference voltage source which provides a voltage corresponding to the reference voltage value UV.
• the autonomously operating electrical voltage limiter 6 limits the voltage increase in comparison to a protection circuit according to the prior art immediately to the predetermined, maximum permissible voltage limit UG.
• the inverter 1 shown differs from the
• the intermediate circuit 2 comprises a series circuit of two DC link capacitors 8.
• a DC link resistor RS is connected in parallel with the DC link capacitors 8.
• the two resistors RS typically have a same resistance, e.g. an ohmic value in the range of 5 to 10 k ⁇ .
• the two series-connected series-connected series resistors RV have approximately the same resistance value as the two intermediate circuit resistors RS.
• the protective circuit 5 shown has, for example, a DC contactor 71 and a protective contactor 72 as controllable, mechanical switching elements 7.
• a DC contactor 71 and a protective contactor 72 as controllable, mechanical switching elements 7.
• an excitation coil is designated in each case.
• reference numerals 74, 75 designate a switching contact belonging to DC contactor 71 and to contactor 72, respectively.
• the two contactors 71, 72 are preferably controlled by a control unit of the inverter 1 not further shown.
• both contactors 71, 72 are activated in an opening manner.
• the DC contactor 71 is closed and the contactor 72 is opened in an opening manner.
• the field voltage uF is applied directly to the DC link 2.
• the DC contactor 71 is opened and the isolating contactor 72 is closed to the input-side voltage limitation.
• the comparator or the comparator is designed as a chopper 65 for controlled clocked control of the electronic switching element 64.
• the electronic switching element 64 is preferably a switching transistor designed for switching operation, such as an IGBT.
• the short-term electrical power absorbed falls almost exclusively on the component provided for this purpose in the form of a limiting resistor RB.
• this limiting resistor RB has a resistance value which is lower than the series resistors RV and to the intermediate circuit resistors RS by two to four orders of magnitude.
• the limiting resistor would have a resistance value in the range of 10 to 100 ⁇ .
• this also means that, compared to the series resistors RV and to the intermediate circuit resistors RS, the electrical power drops by more than two to four orders of magnitude.
• the limiting resistor RB can have a size that is drastically smaller compared to a limiting resistor for a permanent absorption of this electrical power.
• the chopper 65 has a pulse width modulator PWM for controlled clocked control of the electronic
• Switching element 64 with a constant switching frequency f on. Due to the pulse-width modulated control, a particularly simple circuit design of the electronic voltage limiter 6 is possible.
• the switching frequency f is typically in the range of 10 kHz. This allows a particularly rapid control intervention to limit the voltage applied to the intermediate circuit 2 DC link voltage uZK on semiconductor tolerable voltage values.
• an input-side protection circuit 5 for protecting an intermediate circuit 2 of an inverter 1 against overvoltages.
• the protective circuit 5 has an intermediate circuit 2 upstream and bridgeable by means of a controllable mechanical switching means 7 ballast element RV for limiting the voltage of the DC link 2 on.
• the mechanical switching means 7 can be controlled in such a way that it opens in the feed-in mode of the inverter 1 at an intermediate circuit voltage uZK greater than a predetermined voltage limit UG.
• the protection circuit 5 has an electronic voltage limiter 6 which is connected downstream of the pre-switching element RV and connected in parallel with the intermediate circuit 2.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Inverter Devices (AREA)
• Protection Of Static Devices (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=41395945

Family Applications (1)

Country Status (5)

Families Citing this family (22)

Family Cites Families (6)

• 2008
  • 2008-10-06 DE DE102008050543A patent/DE102008050543A1/de not_active Withdrawn
• 2009
  • 2009-09-08 CN CN2009801395176A patent/CN102171906A/zh active Pending
  • 2009-09-08 US US13/122,906 patent/US20110194216A1/en not_active Abandoned
  • 2009-09-08 WO PCT/EP2009/061614 patent/WO2010040613A1/de active Application Filing
  • 2009-09-08 EP EP09782749A patent/EP2335333A1/de not_active Withdrawn

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events