NZ624413B2 - Double rectifier for multi-phase contactless energy transfer system - Google Patents

Abstract

Disclosed is a secondary-side rectifier system of an inductive n-phase energy transmission system with n greater than or equal to 3. The energy transmission system has in each phase (W, V, U) a resonant oscillating circuit, each with at least one inductor (Ls) and at least one capacitor (Cs). The secondary-side resonant oscillating circuits are magnetically coupleable to primary-side resonant oscillating circuits. The secondary-side resonant oscillating circuits are star-connected or mesh-connected and are connected to a rectifier via external conductors (L1...Lk...Ln). The rectifier has a series connection of n diodes (D1...Dk...Dn) with identical conducting directions. Rectifier has a smoothing capacitor (Cgr) connected in parallel with the series connection of diodes such that the output voltage (Ua) of the rectifier is applied to the connecting points (A1, A2) of the smoothing capacitor (Cgr). Each external conductor (Lk) is connected to the anode of a respective diode (Dk) for all k = 1 to N. The terminal (A1) is connected to the external conductor (L1) and the cathode of the Nth diode (Dn) is connected to the connecting point (A2). secondary-side resonant oscillating circuits are magnetically coupleable to primary-side resonant oscillating circuits. The secondary-side resonant oscillating circuits are star-connected or mesh-connected and are connected to a rectifier via external conductors (L1...Lk...Ln). The rectifier has a series connection of n diodes (D1...Dk...Dn) with identical conducting directions. Rectifier has a smoothing capacitor (Cgr) connected in parallel with the series connection of diodes such that the output voltage (Ua) of the rectifier is applied to the connecting points (A1, A2) of the smoothing capacitor (Cgr). Each external conductor (Lk) is connected to the anode of a respective diode (Dk) for all k = 1 to N. The terminal (A1) is connected to the external conductor (L1) and the cathode of the Nth diode (Dn) is connected to the connecting point (A2).

Description

Doubler-rectifier for a multi-phase contactless energy transmission system The invention relates to a secondary-side rectifier of an inductive n-phase energy transmission system withN greater than or equal to 3, the energy transmission system having in each phase a resonant oscillating t, each with at least one inductor and at least one capacitor, and the secondary-side resonant oscillating circuits being magnetically coupleable to primary-side resonant oscillating circuits, with the secondary-side nt ating circuits being star-connected or mesh-connected and being connected to a rectifier via external conductors.

For the dimensioning of the series resonant circuits for the secondary part of the contactless energy transmission system, the nominal reactive voltage which y is greater than the active voltage is determinative of the internal voltages within the device. The higher the ance factor of a phase, the higher the reactive power which needs to be compensated by the resonant tors. The relationship between both the inductance factor and the reactive voltage and the number of turns of the winding is a tic one. In contrast, the active voltage relates to the number of turns in a linear way. If we would, at a given output active power, reduce the active voltage of the resonant circuit via the number of turns, the nominal current would increase due to the linear or proportional dependence.

However, since the reactive voltage changes in a quadratic relationship with the number of turns, the reactive power is d. The consequence of this is that the capacitance of the capacitors required for compensation can be reduced which would enable drastic savings in terms of volume, weight and costs.

In contactless energy transmission, usually a e induced in the secondary circuit of an air-gap transformer is rectified. The resulting direct-current voltage is used to supply power to consumers. For high power requirements, the multi-phase layout of the system is of advantage because power density is increased.

Fig. 1 shows a simple secondary rectifier consisting of a diode full bridge.

The secondary side of the energy transmission system shown in Fig. 1 is designed as a three-phase system in which the resonant oscillating circuits that form the three phases consist of the inductors LS and the resonant capacitors CS which are star-connected. The substitute voltage sources Ui stand for the voltages Ui induced in the secondary windings. A three-phase system is the most simple phase contactless energy ission system. However, in principle, this document refers to all possible numbers of phases. Odd numbers are in most cases advantageous.

The full bridge rectifier shown in Fig. 1 generates a direct-current voltage which first and foremost depends on the coupling with the primary circuit and also from the load. Where a constant direct-current voltage is required, the ier voltage le is regulated via a ream DC/DC converter which is not shown.

Fig. 2 shows the secondary side of the energy transmission system with delta-connected phases.

The objective of this present invention is to provide a ier which consists of few electronic components and generates a higher output e than a full bridge rectifier does. Another objective of the invention is to develop the secondary-side rectifier according to the invention in such a way that a variable output voltage can be generated.

This objective is achieved advantageously by means of a secondary-side rectifier having the features of Claim 1. Advantageous further designs of the rectifier according to Claim 1 result from the features of the sub-claims.

The rectifier ing to the invention is advantageously characterised in that only a number of diodes equal to the number of phases and one smoothing capacitor are required. With the same ioning of the number of turns and the other components, the output voltage achieved is twice as high compared to a conventional full bridge rectifier. Where the ed output voltage is not changed compared to an energy transmission system with full bridge rectifier, the number of turns of the transmission coils can advantageously be reduced. As described above, the ve power to be compensated is also reduced which is why the tance of the capacitors can be reduced. As a result of this, the secondary-side pickups of the energy transmission system can advantageously be ed smaller which in addition to costs also saves weight.

Due to the possibility to connect the secondary-side resonant oscillating circuit phases either in a star or a mesh connection, the output voltage can advantageously be adjusted to the respective conditions. However, usually the star connection is to be red. Different output voltages can be achieved with the circuits shown in the table below.

Topology Output voltage Output voltage Three-phase rectifierrectifier in delta connection √2 * Ui according to prior ording to prior art Three-phase rectifierrectifier in star connection √3 √2 Ui according to prior art according to prior art Three-phase doublerdoubler in delta connection 2 √2 Ui according to the inventionaccording to the invention Three-phase doubler in star connectionphase doubler in star connection 2 √3 √2 Uii ing to the invention according to the invention al conductors LLk within the meaning of the invention areare the k = 1 to N connecting conductorsconnecting conductors which t the free ends of the phases of theends of the phases of the star connection or thethe connecting points of the phases of the meshconnecting points of the phases of the mesh connection to the secondarysecondary-side rectifier. Hence, three externalHence, three external conductors L1, L2 and Land L3 have to be connected to the rectifier in the case ofhave to be connected to the rectifier in the case of a three-phase energy transmission energy transmission system.

TheN diodes (D1, Dk,…, D,…, DN) of the rectifier are connected in seriesare connected in series with identical conducting directionsdirections, so that always the cathode ofof diode Dk is electrically connected to the anode of diode DK+1, with k = 1electrically connected to the a k = 1 toN–1. The output-side smoothing capacitor Cside smoothing capacitor Cgr at which the output voltage Uat which the output voltage UA can be picked up is connected in parallel with the series connection of thepicked up is connected in p with the series connection of the N diodes.

The al conductorsexternal conductors Lk, with k = 1 toN, are connected to theare connected to the anode of diode (Dk) tivelyrespectively.

The rectifier circuit according to the inventionaccording to the invention is of a simple layouis of a simple layout and advantageously consists of just a few componentsconsists of just a few components. At a given nominalAt a given nominal power, advantageouslyadvantageously just a small reactive power compensation needs ation needs to be made in the secondary resonant circuit, so that the necessary resonantbe made in the secondary that the ary resonant capacitors can be dimensioned smallercapacitors can be dimensioned smaller. This advantageouslysly reduces the volume and the weight of thethe weight of the secondary side of the energy transmissionenergy transmission . Moreover, a smaller number ofMoreover, a r number of ier diodes is required whichs is required which additionally saves costs and weight. The only disadvantage resulting from the circuit according to the invention is the increased need for smoothing in the output circuit. However, compared to the advantages, this minor antage can be accepted.

By means of an additional switching device, which in particular is made up of just one switching element, all external conductors can be circuited with each other, so that for a short time no current charges the smoothing capacitor. The resonant oscillating circuits are charged during that time. By removing the short-circuit by opening the switching device or the switching element, the stored energy of the resonant oscillating circuits is used to charge the smoothing capacitor and feed the er. Due the free choice of the pulsing of the switching element, the rectifier can be operated as a step-up converter which advantageously enables the setting or ment of an output voltage which is arbitrary within .

To establish the short-circuit of the external conductors, advantageously just one switch is required in the most simple case which connects the external conductor Ln to the external conductor L1, y all external conductors Lk are short-circuited via the diodes D1 to DN-1. The electrical switching t may be a transistor, in ular a IGBT, JFET or MOSFET, which with its collector, or drain, is connected to the connecting point PN or the external conductor LN and with its emitter, or source, is connected to the connecting point A1, i.e. to ground.

The switching t or the switching device is controlled by means of a control device, the control device controlling the switching device or the switching element in particular by means of a control signal applied to the base, or gate. The required output e or the required output current can be set or adjusted by means of the control device.

In the process, the control device switches on or off the switching element or the switching device, in particular by means of freely adjusting on-off control or pulse width modulation (PWM), and in this way adjusts the output voltage.

To generate little switching loss, the control device switches on the switching element or the switching device only while no voltage is applied to the ing element or the switching device itself. By contrast, it is not decisive that the switching element or the ing device is switched off, or the short-circuit between the external conductors is removed, always only while no current flows through the switch or the diodes.

The ial fact is that the switching element is open for at least one period to allow the free-wheeling of the resonant oscillating circuits. The ing period of the switching element may be a multiple of the resonance period of the transmission frequency of the energy transmission system.

Moreover, the rectifier according to the invention ageously improves the function reliability of the entire system. If one or several diodes of a conventional full bridge rectifier are defective, these diodes usually become low-ohmic which makes the full bridge ier a voltage doubler for the respective phase. The output voltage that increases due to this may damage the downstream electrical ents such as ies or electronic circuits. By contrast, if one or several diodes of the rectifier according to the ion become low-ohmic due to a defect or destruction, this has no negative effect on the downstream components as this fault will reduce the output voltage.

The doubler-rectifier controllable according to the invention advantageously has a higher efficiency because there is no DC/DC converter which is otherwise ed and the voltage element can advantageously be de-energised. Despite the phase system, just one semiconductor switch is required as switching element. Due to the smaller reactive power to be compensated, the structural size and the weight of the secondary side of the energy transmission system are reduced. In addition, the system is less expensive because it has fewer components and a DC/DC converter is not needed.

As already explained, the secondary-side ier according to the invention is suitable for an energy transmission system with more than two phases, in particular with an odd number of phases equal to or greater than three.

The invention equally claims an energy transmission system and a pickup in which a secondary rectifier according to the invention is used.

The secondary-side rectifier according to the invention is explained in more detail below with the help of drawings and circuit ms.

The figures show: Fig. 1: The ary side of a three-phase energy transmission system with a downstream full bridge rectifier, with the nt oscillating circuits being star-connected; 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; Fig. 3: A secondary-side rectifier according to the invention for a three-phase energy transmission system in which the rectifier ons as a voltage doubler and the resonant oscillating circuits are star-connected; 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 ating circuits are delta-connected; Fig. 5: Current diagram for a t in accordance with Fig. 3.

Fig. 6: Equivalent circuit diagram for a -phase p converter; Fig. 7: Current and voltage diagram for a single-phase step-up doubler-rectifier in accordance with Fig. 6; 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; Fig. 9: Rectifier according to the invention in accordance with Fig. 4 with an additional switching element for stepping up the output voltage; Fig. 10: Current and voltage diagram for a three-phase step-up doubler-rectifier in accordance with Fig. 8 or 9; Fig. 11: Rectifier according to the ion with an additional switching element for stepping up the output voltage for anN-phase energy transmission system in which the secondary-side resonant oscillating circuits are star-connected; Fig. 12: Rectifier in accordance with Fig. 11 in which the secondary-side resonant oscillating circuits are mesh-connected.

Compared to the conventional three-phase full bridge rectifiers shown in Fig. 1 and 2, the secondary-side ier according to the invention, as shown in Fig. 3 and 4 for the star-connection and the delta-connection of the secondary-side resonant oscillating ts, requires just half the number of diodes. The connection of the external conductors L1, L2 and L3 to the diodes D1, D2 and D3 is not different for the onnection and the delta-connection. The effect of the circuit is that the concatenated induced voltages Ui of the ary circuit of a three-phase system are d.

For the star-connection in ance 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 und W during one half period. During the short-circuit via the respective diode(s), the respective nt capacitor CS is charged to the peak voltage of the respective phase. In the subsequent other half , the resonant ating circuit runs free on the load circuit with the smoothing capacitor Cgr 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 UA at the output of the rectifier is twice as high as in a conventional B6-rectifier in accordance with Fig. 1 and 2.

Fig. 5 shows the curves of the individual currents during the phases u, v and w and the curve of the rectifier t Igr in the smoothing capacitor Cgr for a circuit in accordance with Fig. 3 or 4. Due to the voltage doubler, the current Igr is interrupted for a period of 120°. Therefore, to achieve sufficient smoothing, it may be necessary to use a smoothing capacitor Cgr with a greater capacitance.

Using Fig. 6 to 10, it is explained how the doubling ts shown in Fig. 3 to 5 can be converted by simple means into rectifiers that allow adjustment/regulation of the output voltage.

For a better tanding, a single-phase doubler will firstly be explained using Fig. 6 in which a series resonant circuit LS-CS 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 t, charging the resonant circuit. As soon as the semiconductor switch S opens, the resonant circuit LS-CS discharges to the output capacitor Cgr and in this way passes its power to the load. In this way, the switching element S has ted the mere doubler-rectifier into a step-up converter, which is operated in the AC circuit. The switch S may be ed either synchronously with the current Igr , 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 rgised. 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 .

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 , or switched on, the diode D1 is shorted, so that Igr 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 CS are rged and the current Igr s the smoothing capacitor. Depending on the on of the switched-on time and the duration of the ed-off time of the ing element S and in dependence on the value of the load, a certain output voltage UA is adjusted or, in the case of variable switched-on and switched-off times, regulated.

The switching principle bed in Fig. 6 and 7 can also be applied to a multi-phase energy transmission . 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 Fig. 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 D1 and D2 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.

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 Igr flows to the output circuit, so that the smoothing capacitor Cgr 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 T2 or T4 (G = 0), the t Igr , 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 Cgr , ng the smoothing capacitor Cgr and in this way causing the output voltage UA to rise. Based on the duty cycle chosen between ed-on and switched-off time, the output e UA can be adjusted upward or stepped up to a certain voltage.

To step the output voltage UA up to a maximal output voltage UA,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 UA may be provided.

Fig. 11 and 12 show circuits for an energy transmission system with more than three phases. It can be seen that always just N diodes Dk are required for ase transmission . Just one switching element S is required for stepping up, irrespective of the number of phases.

Claims (16)

Patent claims

1. Secondary-side rectifier of an inductive n-phase energy transmission system with n greater than or equal to 3, the energy transmission system having in each phase (W, V, U) a resonant oscillating circuit, 5 each with at least one inductor (LS) and at least one capacitor (CS), and the secondary-side resonant oscillating circuits being magnetically coupleable to primary-side resonant oscillating ts, with the secondary-side resonant oscillating circuits being star-connected or mesh-connected and being connected to a rectifier 10 via al conductors (L1, …,Lk,…., LN), characterised in that the rectifier has a series connection of n diodes (D1, Dk,…, DN) with identical conducting directions, with a smoothing capacitor (Cgr ) connected in parallel with the series connection and the output voltage (U A) of the rectifier being applied to the ting points (A1, A2) of 15 the ing tor (Cgr ), the external conductor (Lk) being connected to the anode of the diode (Dk) for all k = 1 to N, the terminal (A 1) being connected to the external tor (L1) and the cathode of theNth diode (DN) being connected to the connecting point (A2).

2. ary-side rectifier according to Claim 1, characterised in that 20 all external conductors (L1,…, Lk,…, LN) can optionally be short-circuited with each other by means of a switching device, wherein the switching device is, in particular, ed by one single ing element (S).

3. ary-side rectifier according to Claim 1 or 2, characterised in 25 that the electrical switching element (S) connects the connection point (PN) or the external conductor (LN) to the connecting point (A1).

4. Secondary-side rectifier according to Claim 2 or 3, characterised in that the electrical switching element (S) is a transistor, in particular an IGBT, JFET or MOSFET. 30

5. Secondary-side rectifier according to Claim 4, characterised in that the transistor (S) with its collector, or drain, is connected to the connection point (PN) or the external conductor (LN) and with its emitter, or source, is connected to the connecting point (A1).

6. Secondary-side rectifier according to one of the Claims 2 to 5, 5 characterised in that a control device (E) ls the switching device or switching element (S), in particular by means of a control signal (G) applied to the base, or gate.

7. Secondary-side rectifier according to Claim 6, characterised in that the control device (E) adjusts the output e (U A,ist ) or the output 10 current to a desired output voltage (UA,soll ) or a desired output current by means of the switching device or switching element (S).

8. Secondary-side rectifier according to Claim 7, characterised in that the l device (E) switches on or off the ing element or switching device (S), in particular by means of freely adjusting on-off 15 control or pulse width modulation (PWM), and in this way adjusts a desired output voltage (UA,soll ) or a desired output current.

9. Secondary-side rectifier according to one of the preceding , terised in that the control device (E) switches off the switching element or ing device (S), and in this way removes 20 the short-circuit between the external conductors, only if no current flows through the switch (S) or the diodes (D1 to DN-1).

10. Secondary-side rectifier according to one of the preceding Claims, characterised in that the device (E) switches on the switching element (S) only if no voltage is applied to the switching element (S). 25

11. Secondary-side rectifier according to one of the preceding Claims, characterised in that the device (E) switches the switching element (S), for the e of adjusting or regulating the output voltage UA or the output current IA, with a ncy which is lower than or equal to the transmission frequency of the energy transmission system.

12. ary-side rectifier according to one of the preceding Claims, characterised in that the switching period of the switching element (S) is a multiple of the period of the transmission frequency of the energy transmission system. 5

13. Secondary-side rectifier according to one of the preceding Claims, characterised in that the switching element (S) is open for at least one period of the energy transmission frequency to allow the free-wheeling of the resonant oscillating ts.

14. Secondary-side rectifier according to one of the preceding Claims, 10 characterised in that the energy transmission system has three, five, seven or 2n+1 phases.

15. Pickup for a multi-phase energy transmission system with star-connected or onnected ary-side resonant oscillating circuits and a secondary-side rectifier ing to one of 15 the Claims 1 to 14.

16. Multi-phase energy transmission system with star-connected or mesh-connected secondary-side resonant oscillating circuits with a secondary-side rectifier according to one of the Claims 1 to 14.