Abstract
A secondary-side rectifier of an inductive n-phase energy transmission system with N greater than or equal to 3, the energy transmission system including in each phase a resonant oscillating circuit, each resonant oscillating circuit including at least one inductor and at least one capacitor wherein secondary-side resonant oscillating circuits are magnetically coupleable to primary-side resonant oscillating circuits, wherein the secondary-side resonant oscillating circuits are star-connected or mesh-connected and are connected to a rectifier via external conductors, wherein the rectifier includes a series connection of a plurality of diodes with identical conducting directions, wherein a smoothing capacitor is connected in parallel with the series connection and an output voltage of the rectifier is applied to connecting points of the smoothing capacitor wherein each external conductor is connected to an anode of the diodes.
Claims
1. A secondary-side rectifier of an inductive n-phase energy transmission system with n being an integer greater than or equal to 3, the energy transmission system comprising: in each phase a resonant oscillating circuit, each resonant oscillating circuit including at least one inductor and at least one capacitor, wherein the resonant oscillating circuits are star-connected or mesh-connected, the rectifier connected to the oscillating circuits via conductors, wherein the rectifier comprises a series connection of a plurality of diodes with identical conducting directions, wherein, with respect to the oscillating circuits, a first diode of the series connection of diodes is directly connected only between a first pair of the oscillating circuits and wherein a second diode of the series connection of diodes is directly connected only between a second, different pair of the oscillating circuits, each conductor being connected to an anode of one of the diodes, a smoothing capacitor, connected in parallel with the series connection of diodes, wherein a first connecting point of the smoothing capacitor is connected via one of the conductors to an anode of the first diode of the series connection of diodes, and a second connecting point of the smoothing capacitor is connected to a cathode of a last diode of the series connection of diodes, and an output voltage of the rectifier is generated at the first connecting point and the second connecting point of the smoothing capacitor.
2. The secondary-side rectifier according to claim 1, wherein two of the conductors are short-circuited with each other by a switching device.
3. The secondary-side rectifier according to claim 2, wherein the switching device connects the first connecting point or one of the conductors to the second connecting point.
4. The secondary-side rectifier according to claim 2, wherein the switching device is a transistor.
5. The secondary-side rectifier according to claim 4, wherein the transistor with an emitter, or a drain, is connected to the first connecting point or one of the conductors and, via a collector or source, is connected to the second connecting point.
6. The secondary-side rectifier according to claim 2, wherein the switching device is controlled via a control signal applied to a base or a gate.
7. The secondary-side rectifier according to claim 6, wherein the output voltage or an output current of the rectifier is adjusted to a desired output voltage or a desired output current via the switching device.
8. The secondary-side rectifier according to claim 7, wherein on or off switching of the switching device is controlled via a freely adjusting on-off control or pulse width modulation, and in this way adjusts the desired output voltage or the desired output current.
9. The secondary-side rectifier according to claim 2, wherein the switching device is switched off, and in this way removes the short-circuit between the conductors, only if no current flows through the switching device or the diodes.
10. The secondary-side rectifier according to claim 2, wherein the switching device is switched on only if no voltage is applied to the switching device.
11. The secondary-side rectifier according to claim 2, wherein the switching device is switched, for adjusting or regulating the output voltage or an output current of the rectifier, with a frequency which is lower than or equal to a transmission frequency of the energy transmission system.
12. The secondary-side rectifier according to claim 11, wherein the switching device is open for at least one period of the transmission frequency to allow free-wheeling of the resonant oscillating circuits.
13. The secondary-side rectifier according to claim 2, wherein the switching device has a switching period that is a multiple of a period of a transmission frequency of the energy transmission system.
14. The secondary-side rectifier according to claim 13, wherein the switching device is open for at least one period of the transmission frequency to allow free-wheeling of the resonant oscillating circuits.
15. The secondary-side rectifier according to claim 2, wherein the switching device is a single electrical switching element.
16. The secondary-side rectifier according to claim 1, wherein the energy transmission system has three, five, seven or 2n+1 phases.
17. A secondary-side pickup for an n-phase energy transmission system with star-connected or mesh-connected resonant oscillating circuits and the secondary-side rectifier according to claim 1.
18. An n-phase energy transmission system with star-connected or mesh-connected resonant oscillating circuits with the secondary-side rectifier according to claim 1.
19. The secondary-side rectifier according to claim 1, wherein a number of diodes of the plurality of diodes equals n.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The figures show:
(2) FIG. 1: The secondary side of a three-phase energy transmission system with a downstream full bridge rectifier, with the resonant oscillating circuits being star-connected;
(3) FIG. 2: The secondary side of a three-phase energy transmission system with a downstream full bridge rectifier, with the resonant oscillating circuits being delta-connected;
(4) FIG. 3: A secondary-side rectifier according to the invention for a three-phase energy transmission system in which the rectifier functions as a voltage doubler and the resonant oscillating circuits are star-connected;
(5) FIG. 4: A secondary-side rectifier according to the invention for a three-phase energy transmission system in which the rectifier functions as a voltage doubler and the resonant oscillating circuits are delta-connected;
(6) FIG. 5: Current diagram for a circuit in accordance with FIG. 3.
(7) FIG. 6: Equivalent circuit diagram for a single-phase step-up converter;
(8) FIG. 7: Current and voltage diagram for a single-phase step-up doubler-rectifier in accordance with FIG. 6;
(9) FIG. 8: Three-phase rectifier according to the invention in accordance with FIG. 3 with an additional switching element for stepping up the output voltage;
(10) FIG. 9: Rectifier according to the invention in accordance with FIG. 4 with an additional switching element for stepping up the output voltage;
(11) FIG. 10: Current and voltage diagram for a three-phase step-up doubler-rectifier in accordance with FIG. 8 or 9;
(12) FIG. 11: Rectifier according to the invention with an additional switching element for stepping up the output voltage for an N-phase energy transmission system in which the secondary-side resonant oscillating circuits are star-connected;
(13) FIG. 12: Rectifier in accordance with FIG. 11 in which the secondary-side resonant oscillating circuits are mesh-connected.
DETAILED DESCRIPTION OF THE INVENTION
(14) Compared to the conventional three-phase full bridge rectifiers shown in FIGS. 1 and 2, the secondary-side rectifier according to the invention, as shown in FIGS. 3 and 4 for the star-connection and the delta-connection of the secondary-side resonant oscillating circuits, requires just half the number of diodes. The connection of the external conductors L.sub.1, L.sub.2 and L.sub.3 to the diodes D.sub.1, D.sub.2 and D.sub.3 is not different for the star-connection and the delta-connection. The effect of the circuit is that the concatenated induced voltages U.sub.i of the secondary circuit of a three-phase system are doubled. For the star-connection in accordance with FIG. 3, this is achieved by means of the diodes D1 and D2. Diode D1 short-circuits the phases U and V during one half period. Diode D2 short-circuits the phases V and W during one half period. The series connection of the diodes D1 and D2 short-circuits the phases U and W during one half period. During the short-circuit via the respective diode(s), the respective resonant capacitor C.sub.S is charged to the peak voltage of the respective phase. In the subsequent other half period, the resonant oscillating circuit runs free on the load circuit with the smoothing capacitor C.sub.gr via diode D3 and charges it to the sum of the currently induced voltage and the stored capacitor voltage of the previous half period. Accordingly, the output voltage U.sub.A at the output of the rectifier is twice as high as in a conventional B6-rectifier in accordance with FIGS. 1 and 2.
(15) FIG. 5 shows the curves of the individual currents during the phases u, v and w and the curve of the rectifier current I.sub.gr in the smoothing capacitor C.sub.gr for a circuit in accordance with FIG. 3 or 4. Due to the voltage doubler, the current I.sub.gr is interrupted for a period of 120. Therefore, to achieve sufficient smoothing, it may be necessary to use a smoothing capacitor C.sub.gr with a greater capacitance.
(16) Using FIGS. 6 to 10, it is explained how the doubling circuits shown in FIGS. 3 to 5 can be converted by simple means into rectifiers that allow adjustment/regulation of the output voltage.
(17) For a better understanding, a single-phase doubler will firstly be explained using FIG. 6 in which a series resonant circuit L.sub.S-C.sub.S can be shorted for a short time via a semiconductor switch S. During the short-circuit, the current of the positive half period flows only in the resonant circuit, charging the resonant circuit. As soon as the semiconductor switch S opens, the resonant circuit L.sub.S-C.sub.S discharges to the output capacitor C.sub.gr and in this way passes its power to the load. In this way, the switching element S has converted the mere doubler-rectifier into a step-up converter, which is operated in the AC circuit. The switch S may be switched either synchronously with the current I.sub.gr, so that the switched-on time is the manipulated variable. However, it is also possible to switch only when a current is flowing through the antiparallel diode and hence the switch S is de-energised. In the latter variant, the manipulated variable is the ratio of the switched-on time to the switched-off time. The switched-on time of the switching element S is in most cases a multiple of the period of the transmission frequency of the energy transmission system.
(18) FIG. 7 shows the currents and voltages of the single-phase controllable doubler-rectifier shown and explained in FIG. 6 during the time in which the switching element S is not switched on and hence the resonant oscillating circuit is not short-circuited. As soon as the switching element S is closed, or switched on, the diode D1 is shorted, so that I.sub.gr becomes zero, the output voltage starting to drop at the same time. As soon as the switching element S is opened, the charged resonant circuit capacitors C.sub.S are discharged and the current I.sub.gr charges the smoothing capacitor. Depending on the duration of the switched-on time and the duration of the switched-off time of the switching element S and in dependence on the value of the load, a certain output voltage U.sub.A is adjusted or, in the case of variable switched-on and switched-off times, regulated.
(19) The switching principle described in FIGS. 6 and 7 can also be applied to a multi-phase energy transmission system. If we adapt the switching principle of the circuit shown in FIG. 6 to a multi-phase system, all phases u, v, w need to be shorted to guarantee the symmetry of the system. The invention achieves this by means of the switching element S shown in FIGS. 8 and 9. The switching element S in the form of a semiconductor switch short-circuits the outermost phases with each other, so that the diodes D.sub.1 and D.sub.2 located between them also become conductive and contribute to the short-circuit. The same rectifier circuit can be used both for the star and the delta connection of the phases u, v and w.
(20) The behaviour of the currents and voltages during the switching operation is shown in FIG. 10. While the semiconductor switch S is closed (G=1), no current I.sub.gr flows to the output circuit, so that the smoothing capacitor C.sub.gr starts discharging via the load which is not shown in the figure. During that time, the energy transmitted by the primary side of the energy transmission system is stored in the resonant circuit. When the switching element S is opened at the time T.sub.2 or T.sub.4 (G=0), the current I.sub.gr, in the form of the combination of the stored half periods and the currently induced half period, flows to the load and the smoothing capacitor C.sub.gr, charging the smoothing capacitor C.sub.gr and in this way causing the output voltage U.sub.A to rise. Based on the duty cycle chosen between switched-on and switched-off time, the output voltage U.sub.A can be adjusted upward or stepped up to a certain voltage.
(21) To step the output voltage U.sub.A up to a maximal output voltage U.sub.A,max, the switching element S is closed for about 95% of a cycle and opened for about 5%. To achieve good smoothing, either the capacitance of the smoothing capacitor Cgr may be increased or at least one additional smoothing stage for smoothing the output voltage U.sub.A may be provided.
(22) FIGS. 11 and 12 show circuits for an energy transmission system with more than three phases. It can be seen that always just N diodes D.sub.k are required for an N-phase transmission system. Just one switching element S is required for stepping up, irrespective of the number of phases.
