The invention relates to a 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 a resonant oscillating circuit,
each with at least one inductor and at least one capacitor, and the
5 secondary-side resonant oscillating circuits being magnetically coupleable
to primary-side resonant oscillating circuits, with the secondary-side
resonant oscillating 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
10 part of the contactless energy transmission system, the nominal reactive
voltage which usually is greater than the active voltage is determinative
of the internal voltages within the device. The higher the inductance
factor of a phase, the higher the reactive power which needs to be
compensated by the resonant capacitors. The relationship between both
15 the inductance factor and the reactive voltage and the number of turns of
the winding is a quadratic 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
20 proportional dependence. However, since the reactive voltage changes in
a quadratic relationship with the number of turns, the reactive power is
reduced. 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.
25 I n contactless energy transmission, usually a voltage 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.
30 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 multi-phase contactless energy
5 transmission 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
10 and also from the load. Where a constant direct-current voltage is
required, the rectifier voltage variable is regulated via a downstream
DC/DC converter which is not shown.
Fig. 2 shows the secondary side of the energy transmission system with
delta-connected phases.
15 The objective of this present invention is to provide a rectifier which
consists of few electronic components and generates a higher output
voltage 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.
20 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 subclaims.
The rectifier according to the invention is advantageously characterised in
25 that only a number of diodes equal to the number of phases and one
smoothing capacitor are required. With the same dimensioning 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 required output voltage is not changed compared to an energy
30 transmission system with full bridge rectifier, the number of turns of the
transmission coils can advantageously be reduced. As described above,
the reactive power to be compensated is also reduced which is why the
capacitance of the capacitors can be reduced. As a result of this, the
secondary-side pickups of the energy transmission system can
advantageously be designed smaller which in addition to costs also saves
5 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 preferred. Different output voltages
10 can be achieved with the circuits shown in the table below.
I T O P O ~ O ~ Y I output voltage
I Three-phase rectifier in delta connection I according to prior art
I
Three-phase rectifier in star connection 1 \ 3 \ Z U 1 according to prior art
/~hree-phaseoubblr in delta connection 21-2 U I according to the invention I --
-;doubler in star connection 7 J-ZU- I according to the invention I
External conductors Lk within the meaning of the invention are the k = 1
to N connecting conductors which connect the free ends of the phases of
5 the star connection or the connecting points of the phases of the mesh
connection to the secondary-side rectifier. Hence, three external
conductors L,, L2 and Lj have to be connected to the rectifier in the case
of a three-phase energy transmission system.
The N diodes (Dl, Dk,..., DN) of the rectifier are connected in series with
10 identical conducting directions, so that always the cathode of diode Dk is
electrically connected to the anode of diode DK+~w,i th k = 1 to N-1. The
output-side smoothing capacitor C,, at which the output voltage UA can
be picked up is connected in parallel with the series connection of the N
diodes. The external conductors Lk, with k = 1 to N, are connected to the
15 anode of diode (Dk) respectively.
The rectifier circuit according to the invention is of a simple layout and
advantageously consists of just a few components. At a given nominal
power, advantageously just a small reactive power compensation needs
to be made in the secondary resonant circuit, so that the necessary
20 resonant capacitors can be dimensioned smaller. This advantageously
reduces the volume and the weight of the secondary side of the energy
transmission system. Moreover, a smaller number of rectifier diodes 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 disadvantage can be accepted.
5 By means of an additional switching device, which in particular is made
up of just one switching element, all external conductors can be shortcircuited
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
10 or the switching element, the stored energy of the resonant oscillating
circuits is used to charge the smoothing capacitor and feed the
consumer. 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 adjustment of an output voltage
15 which is arbitrary within limits.
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 L, to the external conductor L1, whereby all external
conductors Lk are short-circuited via the diodes Dl to DN-1. The electrical
20 switching element may be a transistor, in particular 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 All i.e. to ground.
The switching element or the switching device is controlled by means of a
25 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 voltage 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
30 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 switching element or the switching device itself. By contrast, it is
5 not decisive that the switching element or the switching 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 essential fact is that the switching element is open for at least one
10 period to allow the free-wheeling of the resonant oscillating circuits. The
switching 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 advantageously
15 improves the function reliability of the entire system. I f one or several
diodes of a conventional full bridge rectifier are defective, these diodes
usually become low-ohmic which makes the full bridge rectifier a voltage
doubler for the respective phase. The output voltage that increases due
to this may damage the downstream electrical components such as
20 batteries or electronic circuits. By contrast, if one or several diodes of the
rectifier according to the invention 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
25 advantageously has a higher efficiency because there is no DC/DC
converter which is otherwise required and the voltage element can
advantageously be de-energised. Despite the multi-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
30 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 rectifier according to the
invention is suitable for an energy transmission system with more than
5 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
10 more detail below with the help of drawings and circuit diagrams.
The figures show:
Fig. 1:
15 Fig. 2:
Fig. 3:
Fig. 4:
Fig. 5:
Fig. 6:
The secondary side of a three-phase energy transmission
system with a downstream full bridge rectifier, with the
resonant oscillating circuits being star-connected;
The secondary side of a three-phase energy transmission
system with a downstream full bridge rectifier, with the
resonant oscillating circuits being delta-connected;
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;
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;
Current diagram for a circuit in accordance with Fig. 3.
Equivalent circuit diagram for a single-phase step-up
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 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;
15 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 rectifier according to the invention, as
shown in Fig. 3 and 4 for the star-connection and the delta-connection of
20 the secondary-side resonant oscillating circuits, requires just half the
number of diodes. The connection of the external conductors Ll, Lz and L3
to the diodes Dl, D2 and D3 is not different for the star-connection and
the delta-connection. The effect of the circuit is that the concatenated
induced voltages U, of the secondary circuit of a three-phase system are
25 doubled. For the star-connection in accordance with Fig. 3, this is
achieved by means of the diodes D l and D2. Diode D l 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 D l and D2 short-circuits the phases U und W during one half
30 period. During the short-circuit via the respective diode(s), the respective
resonant capacitor Cs 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,: via
diode D3 and charges i t to the sum of the currently induced voltage and
5 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 current I,, in the smoothing capacitor
10 C,, for a circuit in accordance with Fig. 3 or 4. Due to the voltage doubler,
the current I,, is interrupted for a period of 120°. Therefore, to achieve
sufficient smoothing, it may be necessary to use a smoothing capacitor
C,, with a greater capacitance.
Using Fig. 6 to 10, it is explained how the doubling circuits shown in Fig.
15 3 to 5 can be converted by simple means into rectifiers that allow
adjustment/regulation of the output voltage.
For a better understanding, 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-
20 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 Ls-Cs discharges to the output
capacitor Cgr and in this way passes its power to the load. I n this way,
the switching element 5 has converted the mere doubler-rectifier into a
25 step-up converter, which is operated in the AC circuit. The switch S may
be switched either synchronously with the current I,,, 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
30 manipulated variable is the ratio of the switched-on time to the switchedoff
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.
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
5 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 D l is shorted, so that I,, 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
10 capacitors Cs are discharged and the current I,, 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 UA is
adjusted or, in the case of variable switched-on and switched-off times,
15 regulated.
The switching principle described in Fig. 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
20 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 Dl 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 = I)n,o current I,, flows to the output circuit, so that the smoothing
capacitor C, 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 = O), the
current I,,,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, charging the smoothing capacitor C,, and in this way
causing the output voltage UA to rise. Based on the duty cycle chosen
5 between switched-on and switched-off time, the output voltage 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,rnaxt he
switching element S is closed for about 95% of a cycle and opened for
about 5O/0. To achieve good smoothing, either the capacitance of the
10 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 an N-phase transmission system. Just one switching element
15 S is required for stepping up, irrespective of the number of phases.
We claim:
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,
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 circuits,
with the secondary-side resonant oscillating circuits being starconnected
or mesh-connected and being connected to a rectifier via
external conductors (L1, ...,Lk1...., LN), characterised in that the
rectifier has a series connection of n diodes (Dl, DkI..., DN) with
identical conducting directions, with a smoothing capacitor (C,,)
connected in parallel with the series connection and the output
voltage (UA) of the rectifier being applied to the connecting 'points
(A1, A2) of the smoothing capacitor (C,,), the external conductor (Lk)
being connected to the anode of the diode (Dk) for all k = 1 to N,
the terminal (Al) being connected to the external conductor (L1) and
the cathode of the Nth diode (DN) being connected to the connecting
point (A2).
Secondary-side rectifier according to Claim 1, characterised in
that all external conductors (L1, ..., Lk, ..., LN) can optionally be shortcircuited
with each other by means of a switching device, wherein
the switching device is, in particular, provided by one single
switching element (S).
Secondary-side rectifier according to Claim 1 or 2, characterised in
that the electrical switching element (S) connects the connection
point (PN) or the external conductor (LN) to the connecting point
(A1 1.
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.
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 (Al).
Secondary-side rectifier according to one of the Claims 2 to 5,
characterised in that a control device (E) controls the switching
device or switching element (S), in particular by means of a control
signal (G) applied t o the base, or gate.
Secondary-side rectifier according to Claim 6, characterised in
that the control device (E) adjusts the output voltage (UA,lst) or the
output current to a desired output voltage (UA,soll)o r a desired
output current by means of the switching device or switching
element (S).
Secondary-side rectifier according to Claim 7, characterised in
that the control device (E) switches on or off the switching element
or switching device (S), in particular by means of freely adjusting
on-off control or pulse width modulation (PWM), and in this way
adjusts a desired output voltage (UA,soll) or a desired output current.
Secondary-side rectifier according to one of the preceding Claims,
characterised in that the control device (E) switches off the
switching element or switching device (S), and in this way removes
the short-circuit between the external conductors, only if no current
flows through the switch (S) or the diodes (Dl 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).
11. Secondary-side rectifier according to one of the preceding Claims,
characterised in that the device (E) switches the switching
element (S), for the purpose of adjusting or regulating the output
voltage UA or the output current IAwitlh a frequency which is lower
than or equal to the transmission frequency of the energy
transmission system.
12. Secondary-side rectifier according to one of the preceding Claims,
5 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.
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 circuits.
14. Secondary-side rectifier according to one of the preceding Claims,
characterised in that the energy transmission system has three,
five, seven or 2n+l phases.
15 15. Pickup for a multi-phase energy transmission system with starconnected
or mesh-connected secondary-side resonant oscillating
circuits and a secondary-side rectifier according to one of 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.