Title of Invention

AN INVERTER FOR FEEDING SINUSOIDAL CURRENTS INTO AN ALTERNATING CURRENT NETWORK

Abstract

The present invention provides an inverter for feeding sinusoidal currents into an alternating current network having: a) a switching unit for producing positive portion of the network current; b) the switching unit has a fIrst switch and connected in series thereto diode and the current tap is located between the fIrst switch and the diode; c) located in the current tap is a second switch which is closed during the production of the positive portion of the network current; d) in the current tap a decoupling inductor is provided; e) a switching unit for producing negative portion of the network current; f) the switching unit has a third switch and connected in series thereto diode and the current tap is located between the switch and the diode; g) located in the current tap is a fourth switch which is closed during the production of the negative portion of the network current; h) in the current tap decoupling inductor is provided.

Full Text

The invention concerns an inverter for feeding sinusoidal currents into an ac network or into a public power supply network. In the case of such inverters power switches are almost exclusively in the configuration of a three-phase bridge, as shown in Figure 1. Such an inverter produces from a dc/voltage source a multi-phase alternating current of the phases U, V and W. By virtue of the anti-parallel connection of the power switches Tl to T6, as shown in Figure 1. With suitable diodes, a four-quadrant mode of operation is possible and thus such inverter circuit can also be used in highly versatile manner. A disadvantage with such an inverter circuit is that extremely high energy flows occur in the case of a cross-short-circuits of two switches, for example Tl and T2. which usually results in total destruction of the Inverter and possibly causes a fire to break out and thus culminates in destruction of all connected parts of the installation. A further disadvantage is that, with the increase in the dc voltage, the respective components must be of ever increasing quality, which is only possible when using very expensive components. The object of the present invention is to improve the ability to withstand short-circuiting of an inverter and at the same time to avoid the above-described disadvantages and in particular avoid as far as possible the need for expensive individual components. In accordance with the invention that object is attained by an 1nverter having the features according to one of claims 1 to 3. Advantageous developments drew set forth in the append ant claims. The invention is based on the realization that only a single circuit or switching unit is to be used for the production of a half-oscillation of a sinusoidal oscillation. Therefore, for producing a positive half-sonication of a sinusoidal oscillation, a different circuit or switching unit is used, than for producing the negative part of the sinusoidal current. The consequence of this is that the switching units for producing the positive half-oscillation and also the negative half-oscillation of the sinusoidal current are separated from each other and are connected together only by way of common current tapping, wherein the production of the current in a switching portion cannot involve repercussions in the other switching portion because each switching portion is protected in relation to the other by a switch in the current tapping path. The division of the sinusoidal output current of the inverter into a positive and a negative half-oscillation affords the possibility of sharing the dc voltage supply to the two switching portions for the negative and positive half-oscillations. Therefore the part of the inverter which produces the positive half-oscillation can be operated with a dc voltage, for example 660 volts and the switching portion of the inverter which produces the negative half-oscillation of the sinusoidal current can also be operated with a dc voltage, for example Ud2 = 660 volts. As a total dc voltage that then gives double the individual dc voltage, that is to say 1320 volts. That results in double the output power of the inverter overall, when using components which are only designed for a dc voltage of 660 V. The output inductances of the individual switching units of the inverter are al so acted upon for example during the positive current component only with the partial dc voltage Uri and not with the total dc voltage + 1 . That also results in a saving in terms of material and cost. By virtue of the production of a half-oscillation of a sinusoidal oscillation with a single switching unit, the switching units for different half-oscillations can also be arranged remote from each other in spatial terms, which overall improves the safety and security of the inverter and all parts of the switching installation and also considerably simplifies arranging it in terms of the space involved. A particular advantage of the inverter design according to the invention is that the Inductance of the output choke and thus the component costs required for that purpose can be halved. The invention will be described in greater detail hereinafter by means of an embodiment illustrated in the drawing. In the drawing: Figure 1 shows the basic principle of a known inverter. Figure 4 shows a time diagram in respect of the sinusoidal output current with the switches Tl. SI, T2. S2 shown in Figures 2 and 3, Figure 5 shows a circuit diagram of a three-phase inverter according to the invention, Figure 6 shows a circuit diagram illustrating the basic principle of an interconnection of a plurality of switching portions as shown in Figures 2 and 3 to produce a three-phase alternating current, and Figure 6 shows the circuit diagram of the inverter for a single phase. Figure 2 shows a circuit diagram of a transverse branch or a switching unit 1 for producing the positive component of the ac or three-phase network current from a dc voltage Ud. The switching unit 1 comprises a power transistor Tl as a first switch, for example an IGBT (isolated gate bipolar transistor) or GTO (gate turn off thermister) and a diode Dl which is connected in series with the power switch Tl to the dc voltage terminal. The current tapping for the output current is between the power switch Tl and the diode Dl. Disposed in the current tapping is a second switch SI which in turn is connected in series with an output inductor LI. Figure 3 shows in terms of the basic principle involved a circuit diagram of a switching unit for producing the negative part of the ac or three-phase network current with the reciprocal structure to the circuit shown in Figure 2. Figure 4 shows the time diagram of the sinusoidal output current with the switching units 1 and 2 shown in Figures 2 and 3. Also shown therein is the switch-on behaviour in relation to time of the power switches Tl and T2, as well as the switch-on/switch-off behaviour of the switches SI and S2 disposed in the current tapping. During the positive half-wave of the sinusoidal current (top left in Figure 4) only the power switch Tl is switched on and off in the prescribed cyclic mode while the power switch T2 is switched off in that phase. During production of the positive half-wave of the sinusoidal current the switch SI in the current tapping is switched on (closed) while at the same time the other switch S2 in the current tapping for the negative half-wave is switched off (opened). A "serrated" sinusoidal current is produced by a cyclic operation in respect of the on and off switching states of the power switch Tl and the influence of the diode Dl. During the production of the negative half-wave of the sinusoidal current the conditions are precisely the reverse as for the production of the positive half-wave of the sinusoidal current. In production of the negative half-wave the switch SI is switched off while the power switch T2 is switched on and off in a prescribed cyclic mode of operation and the switch 52 is always switched on. In the region of the current maximum of a sinusoidal wave the power switches Tl and T2 respectively are switched on for a longer time than in the region of a lower current level, in particular in the region of the zero-passages. Figures 5 and 6 show the interconnection of a plurality of the switching units shown in Figures 2 and 3. to constitute an inverter in accordance with the invention for producing a three-phase alternating current. The difference between the illustrated circuits is that in Figure 6 the switching portions for producing the negative half-oscillation of the output current are arranged separately from the switching portions for the positive half-oscillation of the output current. In this respect a separate arrangement can also signify that the switching portions are in different spaces and are connected only by way of their common current tapings. The switching units for producing the positive half-wave are connected to the do voltage terminals +Udi and -Udi. The switching portions for producing the negative half-wave of the sinusoidal current are connected to the dc voltage terminals +Ud2 and -Udz- Figure 1 shows the circuit diagram of a known inverter which, by virtue of the anti-parallel connection of the power switches with the diode, permits a four-quadrant mode of operation and can thus be used in a highly versatile inaner as a switching means, but in the case of a cross-short-circuit of two switches such as Tl and T2 however involves the very high risk of a hard short-circuit which can result in total destruction of the inverter and can possibly also cause an outbreak of fire resulting in complete destruction of all parts of the installation connected thereto. To produce the positive half-wave of the output current the known inverter provides that the switches Tl and T2 are successively switched on and off. For a half-wave, this means that Tl and T2 are successively switched on and off a plurality of times during the half-wave, which already from a statistical point of view markedly increases the probability of a cross-short-circuit. in comparison with the structure according to the invention as shown in Figure 5 or Figure 6 respectively. Figure 7 shows the interconnection of a switching portion for the positive half-oscillations of the output current with a switching portion for the negative half-oscillations of the output current for one of the three phases. Hard short-circuits are prevented in principle by virtue of the separate current branches, positive and negative cross-branches - see Figures 2-7 - in the interconnection of the individual switching units -see Figures 5-7. If nonetheless defective switching operations of the power switches in the different switching portions should occur, they are not only mutually decoupled and protected by way of the inductors Lr-L6\ L1-L6. but a short-circuit is definitively also made Impossible by virtue of the fact that the switches S1-S6 disposed in the current tapping prevent one branch having repercussions in the other due to their being switched on and off in opposite relationship. The illustrated inverter design as shown in Figures 2-7 makes it possible to construct inverters involving a very high level of power. The decoupling chokes Lr-L6' between the current tappings of two interconnected switching units can be used at the same time as high-frequency chokes and also as filters for dU/dt-reductlon. That provides that spurious emission is already drastically reduced directly after the power switches T1-T6. The above-described inverter is suitable in particular for wind power converters or another electricity generator producing electrical direct current (for example a solar power installation). In the case of a wind power converter the generator usually produces a direct current or the generator produces an alternating current which however must then be rectified so that it can be converted by means of the above-described inverter into a network current/voltage. To provide an exact sinusoidal shape in respect of the output current it is advantageous if the switching on/off frequency of the power switches Tl (in relation to the positive half-wave) and T2 (in relation to the negative half-wave) respectively in the zero-passage is considerably higher than in the region of the current maxima. In the region of the current maxima the switching on/off frequency of the power switches Tl and T2 respectively is some 100 Hz (for example in the range between 100 and 600 Hz). In the region of the zero passages the switching on/off frequency of the power switches is some kHz (for example between 5 and 18 kHz). Bremen 31st August 2000 Our ref: W1901 KGG/sb Applicant/proprietor: WOBBEN, Aloys Office ref: PCT/EP99/06565 New claims 1 and 2 fist auxiliary petition) 1. An inverter for feeding sinusoidal currents into an ac network comprising: a) a switching unit (1) which produces the positive part of the network current; b) the switching unit has a first switch (Tl, T3, T5) and a diode (Dl, D3, D5) connected in series therewith and the current tapping is between the first switch (Tl, T3, T5) and the diode (Dl, D3, D5); c) disposed in the current tapping is a second switch (SI, S3, 55) which is closed during the production of the positive part of the network current, and d) a decoupling inductor (Ll'-L6') is provided in the current tapping. 2. An inverter for feeding sinusoidal currents into an ac network comprising: a) a switching unit (2) which produces the negative part of the network current; b) the switching unit has a third switch (T2, T4, T6) and a diode (D2, D4, D6) connected in series therewith and the current tapping is between the switch (T2, T4, T6) and the diode (D2, D4, D6); c) disposed in the current tapping is a fourth switch (S2, S4, 56) which is closed during the production of the negative part of the network current, and d) a decoupling inductor (Ll'-L6') is provided in the current tapping. 3. An inverter for feeding sinusoidal currents into an ac network according to claim 1 and claim 2 in which both switching units (1, 2) are connected in mutually parallel relationship. 4. An inverter according to one of the preceding claims wherein a coupling inductor Lr-L6') is provided in the current tapping. 5. An inverter according to one of the preceding claims characterised in 'that to produce a three-phase current there are provided at 1 east three first and three second switch ng units which are respectively connected together. 6. An 1 inverter according to one of the preceding claims characterised in that the first and second switching units are constructed spatially separatedly from each other. 7. An inverter according to one of the preceding claims characterised in that to produce a half-osci11ation of a sinusoidal oscillation only the first or second switch (Tl, T2) of a switching unit (1,2) is respectively switched on and off a plurality of times. 8. An inverter according to one of the preceding claims characterised in that the switches in the current tapping are thrusters. preferably of the GTO or the IGBT type, 9. An inverter according to the preceding claim characterised in that the second (or fourth) switch in the current tapping is opened only when the fourth (or second) switch in the current tapping path is closed. 10. An inverter according to one of the preceding claims characterised in that a plurality of first and second switching units are connected together by way of their current tapping to provide the current of a single phase (U. V. W) of a three-phase current network. 11. A wind power converter or another electricity generating i nstal1ati on producing electrical di recto current having an i inverter according to one of the preceding claims. 12. An inverter for feeding sinusoidal currents into an ac network substantially as herein described with reference to the accompanying drawings. 13. A wind power converter substantially as herein described with reference to the accompanying drawings.

Documents:

in-pct-2001-552-che-abstract.pdf

in-pct-2001-552-che-claims filed.pdf

in-pct-2001-552-che-claims granted.pdf

in-pct-2001-552-che-correspondnece-others.pdf

in-pct-2001-552-che-correspondnece-po.pdf

in-pct-2001-552-che-description(complete)filed.pdf

in-pct-2001-552-che-description(complete)granted.pdf

in-pct-2001-552-che-drawings.pdf

in-pct-2001-552-che-form 1.pdf

in-pct-2001-552-che-form 26.pdf

in-pct-2001-552-che-form 3.pdf

in-pct-2001-552-che-form 5.pdf

in-pct-2001-552-che-other document.pdf

in-pct-2001-552-che-pct.pdf