EP2206211A1 - Procédé et onduleur pour introduire un courant alternatif dans un réseau électrique pour des conditions de charge partielle - Google Patents

Procédé et onduleur pour introduire un courant alternatif dans un réseau électrique pour des conditions de charge partielle

Info

Publication number
EP2206211A1
EP2206211A1 EP07820654A EP07820654A EP2206211A1 EP 2206211 A1 EP2206211 A1 EP 2206211A1 EP 07820654 A EP07820654 A EP 07820654A EP 07820654 A EP07820654 A EP 07820654A EP 2206211 A1 EP2206211 A1 EP 2206211A1
Authority
EP
European Patent Office
Prior art keywords
current
inverter
burst
output current
power
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP07820654A
Other languages
German (de)
English (en)
Inventor
Peter Knaup
Karl Koch
Thomas Lenz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Robert Bosch GmbH
Original Assignee
Voltwerk Electronics GmbH
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 Voltwerk Electronics GmbH filed Critical Voltwerk Electronics GmbH
Publication of EP2206211A1 publication Critical patent/EP2206211A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • 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
    • 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

Definitions

  • the present application is directed to a method for feeding electrical power into a grid by means of an inverter converting electrical energy of a DC link into an output current for feeding into the grid.
  • the invention is further directed to an inverter for feeding electrical power into the grid.
  • the present invention proposes a method for feeding electrical power into a grid according to claim 1 .
  • the inverter comprises an intermediate storage comprising electrical energy and generates a sinusoidal output current having the frequency of the grid. However, in case of light or part load this current is not continuously generated but comprises burst periods. One or a plurality of periods of the basically sinusoidal output current are only generated, when the interme- diate storage of the inverter comprises sufficient energy to generate an output current having a sufficient value, e. g. 50 % amplitude of the nominal value. If there is not enough energy in the intermediate storage to generate a sinusoidal output current having a sufficient value, the inverter will pause and not generate any sinusoidal output current.
  • a burst period provides more energy than is delivered to the inverter with respect to the corresponding period of time. Accordingly, the additional energy needed for the burst period, that is not delivered by an energy source that is connected to the inverter must be stored in this intermediate storage. To be able to provide burst periods, even if there is only very few energy delivered to the inverter, the intermediate storage should be capable of storing at least sufficient energy to generate one burst period.
  • a DC-link comprising a DC-link capacitor is used as the DC-intermediate storage.
  • Such a method can easily be implemented into inverters, such as known inverters already comprising a DC-link having a DC-link capacitor. It might be advantageous to provide a sufficiently large DC-link capacitor or to provide one or a plurality of additional DC-link capacitors to be able to store sufficient energy in the DC-link.
  • an intermediate storage such as an intermediate storage providing a DC current, e.g. as known in current inverters.
  • the inverter will not generate a current having a reduced amplitude but will involve an AC-current burst mode and therefore generate a current having periods of zero Amps (pause) and of at least one period of a sinusoidal current of a proper value (burst period).
  • an output current for feeding into a grid can be provided whereby a sinusoidal current having only a small amplitude can be avoided.
  • the efficiency of the system can be increased in comparison to the state of the art.
  • the amplitude of the output current refers to a peak amplitude of the sinusoidal fundamental wave of the current.
  • other values can be used such as the RMS-value of each period and thus the RMS-value of one complete fundamental wave.
  • the power of the generated output current depends on the relation of burst periods to pausing periods.
  • the mean output power can be defined by the ratio of the generating time to the pausing time. Accordingly, the generating time to pausing time ratio can be set dependent on the electrical energy available in the DC link.
  • the constant value of the generated current is about 20 to 40% of the nominal value and in particular 30 % of the nominal value.
  • Such values are advantageously selected, if the system efficiency has its optimum at about half maximum load.
  • the advantage of increasing the system efficiency can be explained with respect to the relation of the output power of the sinusoidal current P A c and the power received from the DC link:
  • the output power P AC is smaller than the received DC power P DC by the amount of the power loss P /oss -
  • the power loss does not decrease by the same amount.
  • there is no AC power generated in the pauses according to the present invention there is also no power loss with respect to the output current.
  • the energy contained in a single period is fixed and exactly known.
  • the generated current (l A cburst) comprises half the amplitude of the nominal or maximum output current ⁇ Uc max ) the energy of one period ⁇ E AC burst ) can be calculated assuming
  • the power is transmitted burst period by burst period and at least part of the power of a burst period has to be buffered by the grid inverter's DC link or other intermediate storage.
  • generating of the sinusoidal current in the burst period is initiated, when the DC link voltage is above a first voltage threshold value and when a representing fundamental wave representing the current to be generated reaches zero. Accordingly, the voltage of the DC link indicates the available power, in particular the power stored in the DC link.
  • a burst period of at least one period having a sufficient amplitude can only be generated, if there is sufficient DC power available.
  • the output current to be generated must be adapted to the grid and should be started when the corresponding wavelet crosses zero. It is preferred to always generate burst periods of complete periods and in particular to generate the same kind of burst periods i.e. always generate burst periods starting with a rising slope or always generate burst periods starting with a falling slope. Accordingly, the burst periods will always end at a rising slope or a falling slope respectively.
  • the generating of the sinusoidal current in the burst period is stopped, when the DC link voltage is below the first or below a second voltage threshold value and when the sinusoidal cur- rent or a sinusoidal reference current representing the current to be generated reaches zero.
  • One first voltage threshold value of the DC link voltage can be used to decide whether to initiate generating of the sinusoidal current in the burst period or to stop generating a current, for each instance, when the generated current or a reference current reaches zero.
  • the threshold values for initiating and stopping might be different, to achieve a hysteresis.
  • the generated current can be used, if the system is in a burst period. If the system is in a pause period there is no output current and the reference current is used to detect zero and to detect falling or rising slopes.
  • a reference signal is often also used in general for paused periods and burst periods as well because an artificial reference signal is often easier to handle than a measured one.
  • Decomposing the AC output current is in particular advantageous, if only few power is delivered to the inverter.
  • the benefit of decomposing the AC output current into burst periods decreases with increase of available power.
  • the method switches over to a continuous mode in which the AC output current is not decomposed into burst periods. In this continuous mode the AC output current is continuously generated, as generally known in the art. If the available power delivered to the inverter decreases below the first predetermined power threshold value or if the power decreases below a second predetermined power threshold value, the method will switch back to a burst mode. In this burst mode the AC output current is decom- posed into burst periods. I.e. the burst modes are only used, if there is only few power available.
  • the first predetermined power threshold value is larger than the second predetermined power threshold value. In this way, a hysteresis behavior is achieved. I.e. if the available power falls below the second predetermined power threshold value, the method will switch to burst mode. But if the available power rises again above the second predetermined power threshold value, the method will remain in burst mode until the available power also exceeds the first predetermined power threshold value, which is according to this embodiment larger than the second predetermined power threshold value. According to the same principle the method will also not change back to burst mode, if the available power falls again below the first predetermined power threshold value, unless it also falls below the second predetermined power threshold value.
  • the available power is approximately 30 % of the nominal value of the inverter.
  • the first predetermined power threshold value can be 40 % of the nominal value of the inverter and the second predetermined power threshold value can be 20 % of the nominal value of the inverter.
  • the available power it is usually sufficient to measure the currently delivered power and a prediction of available power is avoided.
  • each inverter having a DC link or other intermediate storage and each inverter generating an AC output current decomposed into burst periods, whereby at least one output current is generated by assembling burst periods of the AC output currents of at least two inverters.
  • each inverter would - according to the invention - provide an AC output current decomposed into burst periods. To avoid feeding too many currents decomposed into burst periods into the grid, such currents can be combined.
  • each inverter generating a decomposed AC output current having one burst period followed by two paused periods. These two signals are then assembled to get one current signal comprising two burst periods followed by one paused period.
  • the at least one assembled output current is a continuously sinusoidal output current.
  • three inverters could be provided each generating a decomposed AC output current having one burst period followed by two paused periods. These three decomposed signals could be assembled to one signal comprising only burst periods and no paused periods and thus the assembled signal comprises one continuously sinusoidal output current.
  • This aspect is in particular useful for a system providing a plurality of inverters each having an intermediate storage such as a DC -link.
  • ten inverters could each generate a decomposed signal comprising one burst period followed by nine paused periods, if there is only very few energy or power available.
  • These ten decomposed signals can be assembled to one continuously sinusoidal current. If more energy is available and accordingly each inverter generates two burst periods followed by eight paused periods, the ten decomposed signals can be assembled to one continuously sinusoidal output currents having twice the amplitude of the example given above. Accordingly, the burst periods of all inverters involved are assembled to one continuously sinusoidal current, having an amplitude corresponding to the amount of the available power of all inverters.
  • a single inverter can generate sinusoidal burst periods of almost a constant amplitude.
  • the amplitude of the burst periods of each inverter might slightly vary, e.g. by 20% of an average value. This variation also depends on the number of inverters involved.
  • the proposed invention including the proposed aspects is in particular useful in combination with at least one solar generator, which supplies electrical energy to an intermediate storage such as a DC -link of at least one inverter.
  • an intermediate storage such as a DC -link of at least one inverter.
  • the method for feeding electrical power into a grid allows for the situation, that solar generators supply energy of a varying amount depending on the weather and the time of the day.
  • the invention further proposes an inverter for feeding electrical power into the grid according to claim 15.
  • the inverter comprises an intermediate storage in particular a DC -link adapted to store electrical energy sufficient to generate one burst period of a current having an amplitude in the range of 20 to 40 %, in particular 30 % of the nominal value.
  • the size of the DC -link ensures that at least one complete wavelet can be generated without having a decrease with respect to the amplitude of the wavelet. Furthermore, the inverter can generate an output current of at least one burst period of a current having such an amplitude, even when there is only few DC power available for supplying into the DC -link. In such a case, when only few DC power is available, it just has to be waited until the DC -link is loaded and comprises sufficient energy to generate at least one wavelet.
  • the DC power is supplied by at least one solar generator.
  • a solar generator may comprise one or a plurality of photovoltaic modules.
  • Fig. 1 shows a decomposed output current according to the invention in comparison to an output current having a small amplitude according to the state of the art
  • Fig. 2 is an illustration of one method for feeding electrical power into the grid according to the invention.
  • Figure 1 illustrates the general design of an AC output current decomposed into burst periods 1 in comparison to a continuously sinusoidal current S1 according to the state of the art.
  • the diagram according to figure 1 shows the time on the x- axis and the current on the y-axis.
  • the diagram just shows the principle design of the two signals 1 and S1.
  • the decomposed current signal 1 has an amplitude of 16A in this example and accordingly the y-axis starts at -16A and goes to +16A.
  • the signal S1 according to the state of the art shows a continuously sinusoidal form having a fairly small amplitude.
  • the amplitude of this signal S1 depends on the available power in the corresponding DC link. I. e. if the avail- able power would further decrease, the amplitude of the signal S1 would also further decrease and on the other hand if the available power would increase, the amplitude of the signal S1 would also increase. This would also take place continuously.
  • the decomposed current 1 comprises a burst period 2 having a constant amplitude with respect to further burst periods, which are not shown in figure 1 .
  • the decomposed current 1 comprises periods 8 without any generated current 4. Accordingly, the output current 1 is divided in burst periods 6 and pausing periods 8. If the available power of the corresponding DC link will decrease, the amplitude of the burst period 2 will remain unchanged but the ratio of the burst periods 6 to the pausing periods 8 will decrease. I. e. there will be more pausing periods 8 than burst periods 6. On the other hand, if the available power increases the ratio of burst periods 6 to pausing periods 8 will increase while the amplitude of the burst periods 2 will still remain unchanged.
  • the amplitude of the burst period 2 can also be changed but it is preferred to stay with one amplitude that results in a high conversion efficiency.
  • FIG. 2 illustrates an operation mode of an embodiment of the invention.
  • the system is in a condition providing a pause of the output current. Accordingly, since at least some energy is supplied to a corre- sponding DC link, the voltage at the DC link V D c ⁇ _ increases.
  • the reference current I RE F is monitored.
  • the reference current which is in fact a reference signal, corresponds to the burst period to be generated with respect to frequency and phase.
  • the reference current is not zero and thus the inverter will not start to generate a burst period.
  • the reference current decreased to zero, whereby a value of zero is indicated by the horizontal slashed line. But at T 2 the reference current I RE F comprises a falling slope and thus a burst period is still not generated.
  • the principle of the invention is easily imple- mented. This way the ratio of burst periods 6 to periods of pauses 8 will also automatically decrease or increase if the available power at the DC link decreases or increases respectively.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

La présente invention porte sur un procédé pour introduire de la puissance électrique dans un réseau électrique au moyen d'un onduleur convertissant de l'énergie électrique d'un stockage intermédiaire en courant continu ayant une tension ou un courant continu en un courant de sortie alternatif, la puissance électrique disponible dans le stockage intermédiaire en courant continu étant convertie en une puissance en courant alternatif au moyen d'un courant de sortie alternatif décomposé en périodes de salve, le courant de sortie comprenant des périodes de salve d'un courant sinusoïdal généré ayant la fréquence du réseau électrique et des périodes de pause où aucun courant n'est généré.
EP07820654A 2007-09-27 2007-09-27 Procédé et onduleur pour introduire un courant alternatif dans un réseau électrique pour des conditions de charge partielle Withdrawn EP2206211A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2007/060266 WO2009039888A1 (fr) 2007-09-27 2007-09-27 Procédé et onduleur pour introduire un courant alternatif dans un réseau électrique pour des conditions de charge partielle

Publications (1)

Publication Number Publication Date
EP2206211A1 true EP2206211A1 (fr) 2010-07-14

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP07820654A Withdrawn EP2206211A1 (fr) 2007-09-27 2007-09-27 Procédé et onduleur pour introduire un courant alternatif dans un réseau électrique pour des conditions de charge partielle

Country Status (2)

Country Link
EP (1) EP2206211A1 (fr)
WO (1) WO2009039888A1 (fr)

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4636931A (en) * 1985-06-28 1987-01-13 Shikoku Denryoku Kabushiki Kaisha Photovoltaic power control system
US6800964B2 (en) * 2002-06-10 2004-10-05 Bernhard Beck Plural configurable DC sources to provide optimal power to plural configurable inverters
US7269036B2 (en) * 2003-05-12 2007-09-11 Siemens Vdo Automotive Corporation Method and apparatus for adjusting wakeup time in electrical power converter systems and transformer isolation
DE102005008809A1 (de) * 2005-02-26 2006-10-12 Kostal Industrie Elektrik Gmbh Wechselrichter
US8310094B2 (en) * 2006-01-27 2012-11-13 Sharp Kabushiki Kaisha Power supply system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2009039888A1 *

Also Published As

Publication number Publication date
WO2009039888A1 (fr) 2009-04-02

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