MXPA01002999A - Electrical power transmission system - Google Patents

Abstract

The invention relates to an electrical power transmission system for transmitting electrical power from a generator (2) generating a first inverter voltage to an electrical alternating voltage network (20) via a transmission line (14). Said transmission system comprises a circuit arrangement (4, 6, 8, 10, 12) which converts the first alternating voltage generated by the generator (2) into a first direct voltage and feeds it into the transmission line (14). The system is also provided with a first inverter (18) which is connected to the output of the transmission line (14). Said inverter converts the first direct voltage into a second alternating voltage and feeds it into the alternating voltage network (20). One of the advantages of the invention is that it provides a circuit arrangement (4, 6, 8, 10, 12) which has a converter connection (4, 6, 8) which converts the first alternating voltage generated by the generator (2) into a third alternating voltage. The invention additionally provides a first transformer (10) which converts the third alternating voltage into a fourth alternating voltage, and a first rectifier (12) which converts the fourth alternating voltage into the first direct voltage.

Description

ELECTRICAL ENERGY TRANSMISSION SYSTEM DESCRIPTION OF THE INVENTION The invention relates to an electric power transmission system for transmitting electric power through a transmission line to an AC electrical network from a generator that generates a first inverter voltage, with a circuit arrangement which converts the first alternate voltage generated by the generator into a first continuous voltage and feeds it to the transmission line, and with a first inverter connected to the output of the transmission line and which transforms the first continuous voltage into a second alternate voltage and it feeds it into the alternating current network. Electricity generating systems such as electric generators are usually connected directly to the public supply network. This also applies to wind-based power plants. However, if there is a greater distance to a possible connection point to the public supply network, a transmission line must be provided. If the alternating voltage generated by the generator is fed directly to the transmission line, then reactive powers are presented in the transmission line, and therefore Ref: 127735 greater conduction losses as well as instabilities in the case of longer paths, since the impedance of an alternating current line of this type consists of inductivity, capacity and real resistance. Also, an alternating current line generates an electromagnetic field that can lead to unwanted EMV problems. To avoid the previously mentioned disadvantages, the first alternating voltage generated by the generator is transformed into a first continuous voltage that is then fed to the transmission line. At the end of the transmission line, the continuous voltage becomes a second alternating voltage and is fed into the public supply network which, as is known, is an alternating voltage network. In this case, the second transformed alternating voltage should correspond at least substantially with that of the public supply network in order to avoid compensation currents and higher harmonics. In this known system of high voltage direct current transmission, which is called HGÜ system by its acronym in German, a direct current is supplied to the transmission line with the aid of direct current reactances, whereby the continuous voltage is adjusted accordingly depending on the control of the associated rectifiers and inverters.

With the aid of the invention an electric power transmission system of the type under consideration is now created in which the circuit arrangement comprises a current rectifying circuit that transforms the first alternate voltage generated by the generator into a third alternating voltage, a first transformer that transforms the third alternate voltage into a fourth alternate voltage, and a first rectifier that converts the fourth alternate voltage into the first continuous voltage. The circuit arrangement designed according to the invention allows in a simple manner in particular the generation of high continuous voltages to be fed to the transmission line, by which it is possible to transmit the electric power in a wide range of power on the line of transmission. In the case of the system according to the invention it is possible in a privileged way to keep constant as a basic variable throughout the power range the high continuous voltage that is fed to the transmission line, while the current varies in a correspondingly linear manner depending on the power to be transmitted, for which the current rectifier circuit and / or the first rectifier regulates to a constant value the first continuous voltage that it generates and that is fed to the transmission line. Through this they suppress the reactances of direct current that are required in the case of the transmission of direct current of high tension known. Preferably the frequency of the third alternate voltage is higher than that of the first alternate voltage and in particular should be in a range of approximately 500 to 20, 000 Hz, so that the transformer provided according to the invention assumes the function of what is known as a medium frequency transformer. The current rectifier circuit can also transform the first alternate voltage, which is usually a polyphase voltage, that is an alternate three-phase voltage, into a third single-phase alternating voltage, whereby the complexity of the apparatus is reduced. One embodiment that is currently especially preferred is characterized in that the current rectifier circuit comprises a second rectifier that transforms the first alternate voltage generated by the generator into a second continuous voltage, and a second inverter that transforms the second voltage. continuous generated by the second rectifier in a third alternating voltage. By integrating a DC intermediate circuit of this kind, it is possible to design the second inverter connected in the following with a number of phases at discretion and in particular also as a single-phase inverter. In addition, a DC intermediate circuit of this kind makes it possible in a simple manner to keep substantially the sum of the input voltage in the second inverter, for which purpose an elevator is conveniently provided in the DC voltage intermediate circuit. And is that the second continuous voltage generated by the second rectifier is usually a grossly linear function of the number of revolutions of the generator and therefore is correspondingly variable, so it is transformed by the elevator into a substantially constant continuous voltage. In addition, the first continuous voltage generated by the first rectifier from the fourth alternate voltage and which is fed to the transmission line should generally be higher than the second DC voltage of the DC intermediate circuit. In general, the first rectifier transforms the fourth alternate voltage into a first continuous voltage that is in the range of approximately 10 to 500 kV. The first transformer preferably transforms the third alternating voltage into a fourth alternate voltage of greater amplitude than that of the third alternating voltage to realize the desired generation of a high continuous voltage that is fed into the transmission line.

A filter comprising preferably at least one inductivity connected in series and at least one capacitor connected in parallel to substantially eliminate undesired higher harmonics should preferably be interposed between the current rectifier circuit and the first transformer. To equalize the continuous voltages, at least one capacitor should be connected to ground between the first rectifier and the transmission line and / or between the transmission line and the first inverter. By virtue of the high continuous voltage feeding the transmission line, the high voltage switches of the first inverter must withstand a correspondingly high voltage resistance at the supply point. In order to reduce the resistance to voltage in the high-voltage switches, it is therefore proposed that preferably the first inverter is constituted by several partial inverters connected in series. In a further development of this embodiment, the first inverter is constituted by an even number of several inverters connected in series, and the connection point between the first half of the quantity and the second half of the number of partial inverters meets potential to Earth. To galvanically separate and adapt the tension of the power transmission system with respect to the alternating voltage network or the public supply network can connect the first inverter to the alternating voltage network through a second transformer. For the case that the first inverter is constituted by several partial inverters in the manner previously described, the second transformer comprises several arrangements of primary windings coupled inductively in series according to the number of partial inverters and a common secondary winding arrangement, being that in each case a primary winding arrangement is connected to a partial inverter, so that the second transformer assumes the function of adding the individual powers of the partial inverters. Other preferred embodiments of the invention are characterized in the dependent claims. The power transmission system according to the invention previously described is particularly suitable for connecting wind power plants to the public supply network when it is necessary to transpose greater distances from the respective wind park to a possible connection point. The preferred embodiments of the invention will be explained in greater detail below on the basis of the accompanying drawings. They show: Figure 1 schematically in block diagram the entire electric power transmission system with the wind-based power plant connected on the input side and the closed public supply network connected on the output side; FIG. 2 shows a detailed connection diagram of the arrangement consisting of the first rectifier at whose input the electric generator of the wind-based power plant is connected, the DC intermediate circuit, the first inverter, the filter, the transformer middle frequencies and the second rectifier to whose output the transmission line is connected; 3 shows a detailed connection diagram of the arrangement constituted by the second inverter in a first embodiment whose input connects the transmission line, and the output transformer whose secondary windings are connected to the three-phase public supply network; and Figure 4a and b the connection box of Figure 3 with a second inverter modified in a second mode (Figure 4a) and a third mode (Figure 4b). In the embodiment described below, the electric generator whose generated energy must be fed to a public supply network 20 over greater distances with the aid of a transmission line 14 is part of a power plant based on wind, as can be seen schematically in Figure 1. However we would like to point out at this point that fundamentally the drive form of the electric generator 2 has no influence on the way of functioning of the described circuit below and that the electric generator 2 can alternatively be driven, for example, by hydraulic power or combustion of fossil materials. As can be seen in figure 1, the electric generator 2 of the wind-based power plant is connected to a current rectifier circuit comprising a first rectifier 4, a rectifier circuit 6 intermediate and a first inverter 8. A transformer 10 of half frequencies is connected between the output of the first inverter 8 and the input of the second rectifier 12. At the output of the second rectifier 12 the transmission line 14 is connected over which the generated continuous voltage is transmitted over a greater distance. by the second rectifier 12. The transmission line 14 is connected to a filter 16 which is followed by a second inverter 18 which is connected with its output to the public supply network 20. In the case of the public supply network 20, it is an ordinary polyphase current network with the usual frequency of 50 Hz or 60 Hz. The electric generator 2 of the wind power plant according to figure 1 generates an alternate voltage of three or six phases and feeds it to the first rectifier 4, which transforms the three-phase alternating voltage into a continuous voltage . In the case of the first rectifier 4 it is an ordinary full-wave rectifier of three or six phases which transforms the positive half-wave of each phase into a positive partial voltage on the positive "branch" Ll and the negative half-wave of each phase in a negative partial voltage on the negative "branch" L2 (see figure 2). At this point we would like to point out that alternatively the electric generator 2 can alternatively also generate, for example, a single-phase alternating voltage, for which the first rectifier must be configured as a single-phase rectifier. The continuous voltage generated by the first rectifier 4 is applied to the intermediate voltage circuit 6 to which input a first capacitor 22 connected between the positive branch Ll and the negative branch L2 is provided. In that the continuous voltage generated by the first rectifier 4 is a grossly linear function of the number of revolutions of the electric generator 2, the intermediate circuit 6 of continuous voltage it contains an elevator that transforms this variable continuous voltage into a constant continuous voltage (see figure 2). This elevator comprises a first inductance 24, an IGBT (Insulated Gate Bipolar Transistor or isolated grid bipolar transistor) connected in parallel between the positive branch Ll and the negative branch L2 at the output thereof, and also connected to the output of the inductance 24, a connected diode 28 in series on the positive branch Ll, and at the outlet a second capacitor 30 connected between the positive branch Ll and the negative branch L2 to equalize the continuous voltage. In the embodiment shown in FIG. 2, a first three-phase inverter 8 is connected to the output of the continuous voltage intermediate circuit 6, which converts the continuous voltage back into a three-phase alternating voltage, and this with a frequency of approximately 500 to 20,000 Hz. Connected after the first inverter 8 is a filter 32 consisting of inductivities 34 connected in series and capacitors 36 connected in parallel. The mid-frequency transformer 10 is connected to the filter 32. Inasmuch as the alternating voltage generated by the first inverter 8 is three-phase, the mid-frequency transformer 10 is necessarily a polyphase current transformer. In the embodiment shown in figure 2 the primary and secondary windings of the mid-frequency transformer 10 are respectively connected in star. However, it is also conceivable to alternatively connect the windings in a triangle. The mid-frequency transformer 10 is not only responsible for a potential separation but also for a high multiplication of the voltage, for example of 400 V per phase on the primary side at 70 kV per phase on the secondary side. Next, the second rectifier 12 transforms the three-phase alternating voltage multiplied by the mid-frequency transformer 10 into a high continuous voltage. Due to the three-phase alternating input voltage, the second rectifier 12 which is a full-voltage high-voltage rectifier is configured as a three-phase rectifier, similarly to the first rectifier 4 the positive half-wave of each phase is transformed into a high voltage positive partial continuum + Ud in the positive branch L3 and the negative half-wave of each phase in a high negative partial voltage -Ud in the negative branch L3, in each case with reference to the point Pl according to figure 2, which in the represented embodiment, it is found with ground potential symmetrically between both branches L3 and L4, so that the voltage difference between both branches L3 and L4 is 2Ud. In order to equalize the high continuous voltage generated by the second rectifier 12, a capacitance is connected between both branches L3 and L4, which in the case of the embodiment shown in FIG. 2 is constituted by two capacitors 38 connected in series whose point Pl of Union meets potential to ground. To establish the same amount of voltage difference between the positive branch L3 and the connection point Pl on the one hand and between the connection point Pl and the negative branch L4 on the other hand, both capacitors 38 should have the same impedance values. At this point we want to point out that the first inverter 8, the filter 32, the mid-frequency transformer 10 and the second rectifier 12 can alternatively also be designed, for example, single-phase. In the exemplary embodiment shown according to FIG. 2, the positive branch L3 and the negative branch L4 are connected in each case via a cut-off 42 and a circuit breaker 44 with the associated conductor of the transmission line 14, which has two conductors. With the help of transformer 10 of In this case, it is possible to generate a high continuous voltage, preferably in the range of approximately 10 to 500 kV, which is then fed to the transmission line 14. The continuous high voltage that is fed in this way to the transmission line 14 serves as the basic variable and remains constant throughout the entire power range, while the current flowing through the transmission line 14 varies correspondingly linearly depending on the power to be transmitted. The constant maintenance of the high continuous voltage applied to the transmission line 14 is effected by a corresponding regulation of the elevator contained in the intermediate voltage circuit 6, of the first inverter 8 and / or of the second rectifier 12. While FIG. 2 shows the circuit installed in the generation site of the power transmission system, in figures 3 and 4 the circuit installed in the feeding site is shown. In the case of the embodiment shown in FIG. 3, the transmission line 14 is connected through circuit breakers 46 and circuit breakers 48 to the filter 16 and to the second subsequent inverter 18. The filter 16 also serves to equalize the high continuous voltage that is transmitted by the transmission line 14, and in the represented embodiment is constituted by two capacitors 16a, 16b, which similarly to the capacitors 38 have respectively the same impedance and are connected in series one with respect to the other as well as jointly in parallel between the positive and negative branches, being that the connection point P2 is with potential to ground. In the case of the second inverter 18, it is an ordinary three-phase inverter whose structure is in principle similar to that of the first inverter 8. At the output of the second inverter 18 another filter 50 is connected, which comprises inductivities connected in each phase to equalize the current . The alternating voltage generated by the second inverter 18 from the high continuous voltage is fed to the three-phase network 20 of public supply through the filter 50 and an output transformer 52 connected in continuation thereof. Correspondingly also the output transformer 52 is of three-phase configuration, wherein in the representation according to FIG. 3 both the primary windings Wp and the secondary windings Ws are respectively connected in star. Naturally, it is also imaginable connect the windings of the delta output transformer 52. The output transformer 52 serves for the division of potential. Another task of the output transformer 52 may be to transform the alternating voltage generated by the second inverter 18 to an effective value corresponding to the alternating voltage of the supply network 20. By virtue of the high continuous voltage feeding the transmission line the high voltage switches of the second inverter 18 have to have a correspondingly high resistance to the voltage. Since for the transmission cable 14 the resistance to the voltage against the earth potential largely determines the price and technical feasibility of manufacture, this value should be precisely defined. For this reason, the voltage values of + Ud = + 50 kV and -Ud = - 50 kV are considered to be suitable against ground potential. In order to halve the voltage resistance in the high-voltage switches, an inverter concept according to FIG. 4 is alternatively proposed. This concept proposes an inverter 18 'with two partial inverters 18a' and 18b 'connected in series, being that the point of connection between both partial inverters 18a 'and 18b' is interconnected with the point P2 connection and therefore is found with ground potential. Due to this, the partial inverters 18a 'and 18b only need half the voltage resistance of the inverter 18 (only) shown in FIG. 3. Both partial voltages + Ud and -Ud are regulated by the output currents of the inverters. partial inverters 18a 'and 18b', if, for example, the positive partial voltage + Ud is too high, then the output current of the associated inverter 18a 'is regulated correspondingly higher and vice versa The partial alternating voltages generated by both inverters 18a 'and partial 18b' are added on the primary side by the output transformer 52 'when the output of the first partial inverter 18a' is connected to the first primary windings Wpl and the output of the second partial inverter 18b 'to the second primary windings Wp2, the first and second primary windings Wpl and Wp2 are coupled inductively in series with one another, Figure 4b shows another embodiment of an inverter 18", in which four inverters 18a ', 18b', 18c 'and 18d' are connected in series, the connection point between the second partial inverter 18b '' and the third partial inverter 18c '' being connected to the connection point P2 and it encounters potential to land. In this way it is possible to reduce the tensile strength for each partial inverter compared to the embodiment of Figure 4a, and therefore to a quarter compared to the embodiment of Figure 3. Correspondingly the transformer 52"of this embodiment comprises four primary windings Wpl, Wp2 , Wp3 and Wp4 coupled inductively in series with each other, which are connected correspondingly to the outputs of the partial inverters. The concept of the inverters shown in Figure 4b works in the same way as the concept shown in Figure 4a. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Claims (18)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. System for the transmission of electrical energy to an electrical network of alternating voltage through a line of transmission of direct current from a generator that generates a first alternating voltage, with a circuit arrangement constituted by a first rectifier, a connected elevator after this and a first inverter in turn connected after the elevator, since the first rectifier transforms the first alternate voltage generated by the generator into a first continuous voltage, the elevator transforms the first continuous voltage into a constant continuous voltage and the first inverter transforms to the constant continuous voltage that makes available the elevator in a second alternate voltage.

System according to claim 1, characterized in that the current rectifier circuit and / or the first rectifier regulates the first continuous voltage that is fed to the transmission line to a constant value, so that the continuous voltage fed to the The transmission line varies according to the transmitted electrical power.

System according to claim 1 or 2, characterized in that the current rectifier circuit transforms the first alternate voltage into a third alternating voltage whose frequency is higher than that of the first alternate voltage.

System according to at least one of claims 1 to 3, characterized in that the current rectifier circuit transforms the first alternate voltage into a third alternating voltage whose frequency is within the range of 500 to 20,000 Hz.

5. System according to except one of claims 1 to 4, characterized in that the current rectifier circuit transforms the first alternate voltage into a third single-phase alternating voltage.

System according to at least one of claims 1 to 5, characterized in that the current rectifier circuit comprises a second rectifier that transforms the first alternate voltage generated by the generator into a second continuous voltage, and a second inverter that transforms the second voltage. continuous generated by the second rectifier in the third alternate voltage.

7. System according to claims 5 and 6, characterized in that the second inverter is a single-phase inverter.

System according to claim 6 or 7, characterized in that an elevator is connected between the second rectifier and the second inverter which transforms the second continuous voltage into a constant continuous voltage.

System according to at least one of claims 6 to 8, characterized in that the first rectifier transforms the fourth alternating voltage into a first continuous voltage that is higher than the second continuous voltage.

System according to at least one of claims 1 to 9, characterized in that the first rectifier transforms the fourth alternate voltage into a first continuous voltage which is within the range of 10 to 500 kV.

System according to at least one of claims 1 to 10, characterized in that the first transformer transforms the third alternating voltage into a fourth alternate voltage of greater amplitude than that of the third alternating voltage.

System according to at least one of claims 1 to 11, characterized in that a filter is connected between the current rectifier circuit and the first transformer.

13. System according to claim 12, characterized in that the filter comprises at least one inductivity connected in series and at least one capacitor connected in parallel.

System according to at least one of claims 1 to 13, characterized in that at least one capacitor is connected to ground between the first rectifier and the transmission line and / or between the transmission line and the first inverter.

System according to at least one of claims 1 to 14, characterized in that the first inverter is formed by several partial inverters connected in series.

16. System according to claim 15, characterized in that the first inverter is constituted by an even number of several inverters connected in series, and the connection point meets the potential M to ground between the first half of the quantity and the second half of the number of partial inverters.

System according to at least one of claims 1 to 16, characterized in that the first inverter is connected to the alternating voltage network through a second transformer.

18. System according to claim 17 as well as according to claim 15 or 16, characterized in that the The second transformer comprises several arrays of primary windings inductively coupled in series according to the number of partial inverters, and a common secondary winding arrangement, wherein in each case a primary winding arrangement is connected to a partial inverter. f b / fi itoo? / 0 0 1 ^ SUMMARY OF THE INVENTION The invention relates to a system for transmitting electrical energy to transmit electric power through a transmission line (14) to an electric network (20) of alternating current from a generator (2) that generates a first inverter voltage, with a circuit arrangement (4, 6, 8, 10, 12) that converts the first alternate voltage generated by the generator (2) into a first continuous voltage and feeds it to the transmission line (14), and with a first inverter (18) connected to the output of the transmission line (14) and which transforms the first continuous voltage into a second alternating voltage and feeds it to the alternating current network (20). The particularity of the invention consists in that the arrangement > (4, 6, 8, 10, 12) circuit comprises a current rectifier circuit (4, 6, 8) that transforms the first alternate voltage generated by the generator (2) into a third alternating voltage, a first transformer (10). ) that transforms the third alternate voltage into a fourth alternate voltage, and a first rectifier (12) that converts the fourth alternate voltage into the first continuous voltage. (Figure 1)