DIRECT-CURRENT VOLTAGE CONVERTER FOR BIDIRECTIONAL ELECTRICAL POWER TRANSMISSION FROM A PRIMARY SIDE TO A SECONDARY SIDE OF THE DIRECT-CURRENT VOLTAGE CONVERTER OR VICE VERSA

Abstract

The invention relates to a direct-current voltage converter (10) for electrical power transmission from a secondary side to a primary side of the direct-current voltage converter (10), which has on the primary side an actively clamped flyback converter circuit having a controlled first switch (1) and a controlled second switch (2), and the primary side is inductively coupled to the secondary side. The current of a secondary coil (6) on the secondary side, for inductive coupling to the primary side, is switched by a single controlled third switch (3) on the secondary side, and the direct-current voltage converter has a regulator (12) which, in parts of a regulating cycle, conductively connects the third switch (3) to the first switch (1).

Claims

1. A DC-DC converter (10) for electrical power transmission from a secondary side to a primary side of the DC-DC converter (10), the DC-DC converter 10 comprising: a transformer having a primary-side primary coil (5) and a secondary-side secondary coil (6), wherein the primary coil (5) is connected on one side to a first primary voltage terminal (11a) and is connected on the other side, in series with a first switch (1), to a second primary voltage terminal (11b), wherein, in parallel with the primary coil (5), a capacitor (4) is connected in series with a second switch (2), and wherein the secondary coil (6) is connected on one side to a first secondary voltage terminal (9a) and is connected on the other side, in series with a third switch (3), to a second secondary voltage terminal (9b), and a regulating device (12) configured to switch the first (1), second (2) and third switches (3) off and on repeatedly, wherein the first switch (1) is always switched off when the second switch (2) is switched on, and vice versa, for generating an alternating current in the primary coil (5), and to switch the third switch (3) off and on depending on the switch position of the first switch (1), wherein the regulating device (12) is configured to set a time at which the third switch (3) is switched on to a time before the first switch (1) is switched off and the second switch (2) is switched on in order to enable a power flow on the side of the secondary side to the primary side.

2. The DC-DC converter (10) as claimed in claim 1, wherein the regulating device (12) is configured to set the time at which the third switch (3) is switched on to a time after the first switch (1) is switched off and the second switch (2) is switched on in order to enable a power flow on the side of the primary side to the secondary side.

3. The DC-DC converter (10) as claimed in claim 2, wherein the regulating device (12) is configured to set, depending on a presettable power transmission direction, the time at which the third switch (3) is switched on to a time before or after the first switch (1) is switched off and the second switch (2) is switched on in order to set a power flow corresponding to the preset power transmission direction.

4. The DC-DC converter (10) as claimed in claim 1, wherein at least one of the first (1), the second (2) or the third (3) switch is manufactured on the basis of silicon technology, silicon carbide technology or gallium nitride technology.

5. A method for controlling a DC-DC converter (10) in order to transmit electrical power from a secondary side to a primary side of the DC-DC converter (10), wherein the DC-DC converter (10) has a transformer having a primary-side primary coil (5) and a secondary-side secondary coil (6), wherein the primary coil (5) is connected on one side to a first primary voltage terminal (11a) and is connected on the other side, in series with a first switch (1), to a second primary voltage terminal (11b), wherein, in parallel with the primary coil (5), a capacitor (4) is connected in series with a second switch (2), wherein the secondary coil (6) is connected on one side to a first secondary voltage terminal (9a) and is connected on the other side, in series with a third switch (3), to a second secondary voltage terminal (9b), and has a regulating device (12), the method comprising the following steps: repeated, via the regulating device (12), switching-off and switching-on of the first (1), second (2) and third switches (3), wherein the first switch (1) is always switched off when the second switch (2) is switched on, and vice versa, for generating an alternating current in the primary coil (5), switching-off and switching-on of the third switch (3) depending on the switch position of the first switch (1), and presetting of a time at which the third switch (3) is switched on as a time before the first switch (1) is switched off and the second switch (2) is switched on in order to enable a power flow on the side of the secondary side to the primary side.

6. The method as claimed in claim 5, wherein the regulating device implements further steps: presetting of a time at which the third switch (3) is switched on as a time after the first switch (1) is switched off and the second switch (2) is switched on in order to enable a power flow on the side of the primary side to the secondary side.

7. The method as claimed in claim 6, wherein the regulating device implements the following further steps: determination of a presettable power transmission direction, and presetting of a time at which the third switch (3) is switched on as a time before or after the first switch (1) is switched off and the second switch (2) is switched on depending on the determined power transmission direction.

8. (canceled)

9. A computer-readable storage medium, comprising commands which, when run on a computer, cause said computer to control a DC-DC converter (10) in order to transmit electrical power from a secondary side to a primary side of the DC-DC converter (10), wherein the DC-DC converter (10) has a transformer having a primary-side primary coil (5) and a secondary-side secondary coil (6), wherein the primary coil (5) is connected on one side to a first primary voltage terminal (11a) and is connected on the other side, in series with a first switch (1), to a second primary voltage terminal (11b), wherein, in parallel with the primary coil (5), a capacitor (4) is connected in series with a second switch (2), wherein the secondary coil (6) is connected on one side to a first secondary voltage terminal (9a) and is connected on the other side, in series with a third switch (3), to a second secondary voltage terminal (9b), and has a regulating device (12), and wherein the regulating device repeatedly switches-off and switches-on of the first (1), second (2) and third switches (3), wherein the first switch (1) is always switched off when the second switch (2) is switched on, and vice versa, for generating an alternating current in the primary coil (5), switches-off and switches-on of the third switch (3) depending on the switch position of the first switch (1), and presets a time at which the third switch (3) is switched on as a time before the first switch (1) is switched off and the second switch (2) is switched on in order to enable a power flow on the side of the secondary side to the primary side.

10. A system having: a first DC source having a first voltage; a second DC source having a second voltage, wherein the first voltage is higher than the second voltage; a DC-DC converter as claimed in claim 1, wherein the DC-DC converter (10) is electrically connected on the primary side to the first DC source and is connected on the secondary side to the second DC source having the second voltage.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Exemplary embodiments of the invention are illustrated in FIGS. 1 and 2 and will be explained in more detail below. In the drawing:

[0058] FIG. 1 shows the topology of the DC-DC converter;

[0059] FIG. 2a shows the drive signals of the three switches; and

[0060] FIG. 2b shows the current characteristics of the primary and secondary sides.

DETAILED DESCRIPTION

[0061] FIG. 1 shows a topology of a DC-DC converter 10, in which a first switch 1 is electrically connected to a primary coil 5 of a primary side of the DC-DC converter 10, in a first series circuit. A second switch 2 is arranged on the primary side and is electrically connected to a capacitor 4 in a second series circuit, wherein the second series circuit is connected in parallel with the primary-side primary coil 5. A first contact of the first series circuit on the side of the primary coil 5 is connected to a first primary voltage terminal 11a of the primary side of the DC-DC converter 10, and a second contact of the first series circuit on the side of the first switch 1 is connected to a second primary voltage terminal 11b of the primary side of the DC-DC converter 10. A voltage U1 is present between these terminals 11a and 11b of the primary side. This topology of the primary side of the DC-DC converter represents an example of an actively clamped flyback converter circuit.

[0062] A first DC-link capacitor 7 can be electrically connected, as illustrated above, to the first and second primary voltage terminals 11a, 11b of the primary side.

[0063] The secondary side of the DC-DC converter 10 has a controlled third switch 3, which, with the secondary coil 6 of the secondary side, forms a third electrical series circuit. A first contact of the third series circuit on the side of the secondary coil 6 forms the first secondary voltage terminal 9a of the secondary side of the DC-DC converter 10, and a second contact of the third series circuit on the side of the third switch 3 forms the second secondary voltage terminal 9b of the secondary side of the DC-DC converter 10. The voltage U2 is present between these terminals 9a and 9b of the secondary side.

[0064] A second DC-link capacitor 8 can be electrically connected, as illustrated above, to the first and second secondary voltage terminals 9a, 9b of the secondary side.

[0065] The primary coil 5 of the primary side and the secondary coil 6 of the secondary side are inductively coupled to one another. In particular, the inductances are in the form of windings of a transformer which are DC-isolated from one another.

[0066] In FIG. 1, the controlled switches 1, 2, 3 are in the form of n-channel MOSFET transistors, but it is also possible for other unipolar components to be used for controlling the current flow. Using a unipolar component gives the advantage of the lower on-state voltage, such as in the case of the MOSFET transistor. Examples of this have already been mentioned further above in the description.

[0067] A regulating device 12 is connected with its outputs 12a, 12b and 12c to the control contacts of the second switch 2, the first switch 1 and the third switch 3, respectively. The regulating device 12 is designed to drive the individual switches 1, 2 and 3, for example, corresponding to the drive pattern shown in FIG. 2a. The regulating device 12 controls the control contacts of the three switches 1, 2 and 3 to High or Low, corresponding to the characteristic in FIG. 2a. When the control signal is High, the respective switch is switched so as to be conducting, correspondingly switched on; when the control signal is Low, the respective switch is switched so as to be nonconducting, correspondingly switched off.

[0068] In the case of such a time sequence for the driving of the switches, electrical power is transmitted inductively via the transformer comprising the secondary coil 6 and the primary coil 5 from the secondary side of the DC-DC converter to the primary side. This energy is initially stored in the capacitor 4 and then in the primary coil 5 before this energy is output to a load connected to the primary voltage terminals 11a, 11b.

[0069] FIG. 2b represents the current characteristics I1 in the primary coil 5 and I2 in the secondary coil 6 of the DC-DC converter which result from the described drive pattern, wherein the arrows denoted by I1 and I2 in FIG. 2a in the primary circuit and in the secondary circuit, respectively, of the DC-DC converter 10 specify the current directions at these points in the topology.

[0070] The text which follows describes the current characteristics in FIG. 2b which result from the drive pattern from FIG. 2a, beginning shortly before the third switch 3 of the secondary side is switched so as to be conducting at time t1.

[0071] The primary-side primary coil 5 and the secondary-side secondary coil 6, which are inductively coupled, can be considered to be equivalent in an electrical equivalent circuit diagram used for the following description. An equivalent circuit diagram comprises an ideal transformer between the secondary side and the primary side of the DC-DC converter and a leakage inductance in series with a magnetizing inductance on the primary side, wherein the magnetizing inductance is connected in parallel with the ideal transformer.

[0072] At the beginning of the consideration, prior to time t1, the first switch 1 is conducting. Both the second switch 2 and the third switch 3 are nonconducting.

[0073] Initially, a decaying negative current I1, driven by the magnetizing inductance of the transformer, flows, as a result of which electrical power is transmitted to the primary side.

[0074] If now, at time t1, the third switch 3 is switched so as to be conducting, the ZCS mode takes place since the current I2 is very low. With the third switch 3 conducting, the sum of the two voltages U1 and (transformed by means of the transformer) U2 is present at the leakage inductance. Since the leakage inductance is low in comparison with the magnetizing inductance, the current I2 rises steeply in the negative direction, and power is taken from a second DC voltage source connected to the secondary voltage terminals.

[0075] The voltage U2 transformed by means of the transformer causes a rise in a current through the magnetizing inductance, resulting from a different winding sense of the windings of the transformer, and this rise also results in a change to the mathematical sign of I1. The duration of the overlapping time period 13, i.e. between times t1 and t2, in which the first switch 1 and the third switch 3 are together switched so as to be conducting, can be used for regulating the power transmission.

[0076] At the end of this time period, in which the first switch 1 and the third switch 3 are together switched so as to be conducting, the first switch 1, at time t2, is switched off with low losses. By virtue of the first switch 1 being switched off, the primary-side current I1, commutates, owing to the intrinsic diode, to the reverse-conducting second switch 2, with the result that the second switch S is switched on virtually without any losses, in the ZVS mode.

[0077] In this phase, a low negative voltage is present across the leakage inductance, with this voltage being formed from the difference between a voltage U.sub.Clamp at the capacitor 4 and the voltage U2 transformed by means of the transformer. Therefore, the negative current I2 decreases.

[0078] Virtually the total voltage U2 transformed by means of the transformer is present across the magnetizing inductance, and the current I1 falls correspondingly. Therefore, the energy is stored in the capacitor 4 and in the magnetizing inductance.

[0079] The current I1 through the second switch 2 has changed its direction when this phase ends. The switching-off of the second switch 2 therefore takes place at time t3 with low losses. Thereupon, the current commutates through the magnetizing inductance onto the reverse diode of the first switch 1, with the result that the first switch 1 is switched on, virtually without losses in the ZVS mode at time t3.

[0080] The current I2 through the third switch 3 has decreased to low values and can therefore be switched off with low losses, virtually in the ZCS mode, in particular offset by a time interval with respect to the switch-off signal of switch 2, in synchronism with the second switch 2 at time t3. Alternatively, the third switch 3 is also switched off passively by reverse recovery of the reverse-conducting diode.

[0081] The negative current I1 in the magnetizing inductance now flows to the load which is connected on the primary side to the primary voltage terminals 11a and 11b. In this phase, therefore, the output of the power taken up in the previous phase from the second DC voltage source connected on the secondary side to a first DC voltage source or load connected on the primary side takes place. When the third switch 3 is switched on at t′ 1, in the ZCS mode, with a low current, the described cycle begins from the beginning.

[0082] By way of summary, electrical power is taken up from the secondary side of the circuit and output to the primary side of the circuit. Advantageously, all of the switches are operated, either as the first switch 1 and the second switch 2 in the ZVS mode, or as the third switch 3 in the ZCS mode. The low switching losses at these working points also enable a high switching frequency in the drive pattern or modulation method described here or in this control cycle. Therefore, there is no additional hardware complexity in the circuit in comparison with the operation of the DC-DC converter from the primary side to the secondary side.