DC-DC converter and methods for controlling a DC-DC converter

Abstract

Method for operating a controlled three-phase DC-DC converter, wherein three AC voltage phases are generated from an input voltage of the DC voltage converter by means of an inverter (1) with three half-bridges (10, 12, 14), wherein the three half-bridges (10, 12, 14) are controlled by a respective periodic control signal, in particular to generate a desired control output, which alternates between two control states, wherein the periodic control signals are each phase-shifted by 1 / 3 of a period relative to each other and, when the DC-DC converter is fully driven, the periodic control signals within each period correspond to a step function with one step after each half-period, wherein, to change the output of the DC-DC converter for each input phase within a respective half-period, the control state is switched symmetrically in the middle of the respective half-period for a portion of the respective half-period, in particular, where, therefore, the proportion disappears when the control is fully activated. where a transformer (16) in a delta connection is connected to the three half-bridges (10, 12, 14), wherein the AC voltage phases are connected to a respective phase of a transformer in a delta connection and the transformer converts the three AC voltage phases into three output phases, wherein a rectifier rectifies the converted alternating voltage, the rectified, converted alternating voltage then forms the output voltage of the DC-DC converter.

Description

[0001] The invention relates to a DC-DC converter and a method for controlling a DC-DC converter.

[0002] EP 2 023 472 A1 relates to a clock-controlled DC voltage converter.

[0003] A method for controlling a clock-controlled DC voltage converter is known from EP 1 589 648 A2.

[0004] A three-phase DC / DC converter is known from EP 1 589 648 A2.

[0005] A power inverter for a battery charger is known from US patent 2006 / 0 083 030 A1.

[0006] A multiphase DC / DC converter is known from US 6 944 033 B1.

[0007] The invention is therefore based on the objective of further developing a DC-DC converter and a method for controlling a DC-DC converter, wherein the control is simple.

[0008] According to the invention, the problem is solved in the method according to the features specified in claim 1 and in the arrangement according to the features specified in claim 12.

[0009] Key features of the invention in the method for operating a controlled three-phase DC-DC converter are that three AC voltage phases are generated from an input voltage of the DC-DC converter by means of an inverter with three half-bridges, wherein the three half-bridges are controlled with a respective periodic control signal which switches between two control states, wherein the periodic control signals are phase-shifted by 120° and, at full drive of the DC-DC converter, the periodic control signals correspond to a step function with one step after a half-period, wherein, to change the drive of the DC-DC converter, for each input phase within a respective half-period, the control state is switched symmetrically in the middle of the respective half-period for a portion of the respective half-period.An advantage here is that there is a linear relationship between the proportion and the voltage-time area of ​​the DC-DC converter.

[0010] In an advantageous design, the proportion of the half-cycle is the same for each input phase. An advantage of this is that no DC voltage component is generated at the transformer.

[0011] In an advantageous embodiment, the portion of the 180-degree half-period lies between 0 and 60 degrees. A further advantage is that the voltage-time area is adjustable between a maximum value and 0 Vs.

[0012] In a preferred embodiment, the voltage of the AC phases is generated by switching two switches of the half-bridges. An advantage of this is the simplicity of regulating the output voltage.

[0013] In a preferred embodiment, the voltage states are switched by closing an upper switch of a half-bridge and opening a lower switch. An advantage of this is that a DC voltage component is avoided.

[0014] According to the invention, the AC voltage phases are connected to a respective phase of a transformer in a delta connection, and the transformer converts the three AC voltage phases into three output phases. An advantage of this is that the ripple of the output voltage is reduced.

[0015] In a preferred embodiment, the output phases are rectified. This has the advantage of reducing the ripple of the output voltage.

[0016] In an advantageous embodiment, the three output phases are each rectified by a rectifier circuit and are preferably combined at one point in the circuit, where an output voltage of the DC-DC converter is tapped. An advantage of this is that the ripple of the output voltage is reduced.

[0017] In an advantageous embodiment, each rectifier circuit has two switches which are timed accordingly to rectify the output phases. An advantage of this is that the losses are reduced, since the forward voltage of the switches is lower than that of a rectifier diode.

[0018] In a preferred embodiment, the voltages of the rectified output phases are smoothed using a capacitor. This has the advantage of reducing the ripple of the output voltage.

[0019] In an advantageous embodiment, the switches of the rectifier circuits are operated synchronously with the switches of the inverter in such a way that feedback, i.e., an energy flow from the output side to the input side of the DC-DC converter, is achieved. The advantage here is that energy can be transferred in both directions of the DC-DC converter.

[0020] Key features of the setup are that it is adapted to execute the steps of the procedure described above. A particular advantage is the availability of a DC-DC converter with simple setpoint specification for control at an output frequency close to the clock frequency.

[0021] In a preferred embodiment of the arrangement, the primary and secondary windings of the transformer are wound on a three-legged core of the transformer. The advantage here is that the transformer material is used optimally.

[0022] In a further advantageous embodiment of the arrangement, a center-point rectifier is arranged on the secondary side at the secondary winding, which rectifies the transformer output voltage. An advantage of this is that the ripple of the output voltage is reduced.

[0023] In a further advantageous embodiment of the arrangement, an inductor is connected in series and / or a capacitor is connected in parallel to the output of the DC-DC converter. The advantage of this is that the ripple of the output voltage is reduced.

[0024] Further advantages arise from the dependent claims. The invention is not limited to the combination of features of the claims. For those skilled in the art, further meaningful combinations of claims and / or individual claim features and / or features of the description and / or the figures will become apparent, in particular from the problem statement and / or the problem arising from a comparison with the prior art.

[0025] The invention will now be explained in more detail using exemplary embodiments with reference to the drawing. The drawings show, purely schematically: Fig. 1: the circuit design of a DC-DC converter according to the invention; and Fig. 2: the control signal according to the invention and below each of the corresponding voltage curves of the alternating voltage phases.

[0026] The in Fig. The DC-DC converter shown in Figure 1 essentially has three parts. On the input side, the applied input voltage Uin is converted into an AC voltage by an inverter 1. A transformer 16 converts this AC voltage, and a rectifier rectifies the converted AC voltage. The rectified, converted AC voltage then forms the output voltage of the DC-DC converter.

[0027] An input capacitor 24 is arranged in parallel with the input voltage Uin upstream of inverter 1 as an energy buffer. Inverter 1 comprises three half-bridges, each with two switches. The center taps of the half-bridges are connected in a delta configuration to three input coils of transformer 16.

[0028] Thus, the switch positions of a first half-bridge 10 with switches S1 and S2 and a second half-bridge 12 with switches S3 and S4 are responsible for the voltage U1 at a first input coil of the transformer 16. The voltage U2 at a second input coil of the transformer 16 is determined by the switch positions of the switches S3 and S4 of the second half-bridge 12 and the switches S5 and S6 of the third half-bridge 14 of the inverter. The voltage U3 of a third input coil of the transformer 16 results from the switch positions of the third half-bridge 14 and the first half-bridge 10.

[0029] The switches S1 to S6 of the inverter's half-bridges are controlled by a control device (not shown). These switches S1 to S6 are, for example, semiconductor components such as transistors with antiparallel diodes as freewheeling diodes, or other common component arrangements for implementing an inverter switch.

[0030] Fig. Figure 2 shows the control signal according to the invention for controlling switches S1 to S6 for a period of 360°. The control signals shown a (solid line), b (long dashed line) and c (short dashed line) correspond to the switch states of the first, second and third half-bridge 10, 12, 14, respectively.

[0031] A control signal of 1 means that the upper switch S1, S3, or S5 of the corresponding half-bridge 10, 12, or 14 is closed, and the lower switch S2, S4, or S6 is open. A control signal of -1 means that the corresponding lower switch S2, S4, or S6 is closed, and the corresponding upper switch S1, S3, or S5 of the respective half-bridge 10, 12, or 14 is open. Any dead times to prevent potential voltage or current spikes, where both switches of a half-bridge are open or closed, are not considered here.

[0032] The lower diagrams of the Fig. Figure 2 shows the corresponding voltages U1, U2, and U3, which are generated by the respective switch positions. On the vertical axis, +2 corresponds to a voltage of +Uin and -2 to a voltage of -Uin.

[0033] The two diagrams on the right of the Fig. Figure 2 shows the control signal and the voltage waveforms of U1, U2, and U3 at full output of the DC-DC converter. The control signals a, b, and c form a step function, with one step in each 180° increment, thus representing a change in the position of the corresponding switches from open to closed and vice versa.

[0034] The individual control signals a, b, and c are phase-shifted by 120° relative to each other. This means that they overlap for different fractions of the 360° of a period, and that the plateaus where the control signals assume a constant value are also phase-shifted by 120°.

[0035] Assuming constant switching of switches S1 to S6, for example, the control signals a and b both have the value 1 between 0° and 60°. This means that switches S1 and S3 are closed and switches S2 and S4 are open. Therefore, the voltage at both contacts of the switch is 1. Fig. The coil shown as the uppermost coil of the transformer has the same potential, and therefore the voltage U1 is zero.

[0036] At 60°, the control signal b changes from +1 to -1, thus opening switch S3 and closing switch S4. Now the potential Uin is present at the upper contact of the top coil, and the lower contact is grounded via the closed switch S4. This results in a voltage U1 equal to Uin.

[0037] The other voltage states arise in a corresponding manner. When the polarity is reversed, i.e., for example, with U1's lower contact at potential Uin and the upper contact grounded, the voltage -Uin is then generated across the corresponding coil.

[0038] To control the DC-DC converter, as in the sequence in Fig. The diagrams shown from right to left show that, within each half-period, the control state is changed symmetrically in the middle of that half-period for a portion of that half-period. For example, for the control signal a in the second diagram from the right... Fig. 2. The switch state changes between 80° and 100° and thus symmetrically by 90° from +1 to -1. The proportion in this example is 20°.

[0039] This results in the voltage U1 becoming zero for this period. The same thing happens with the opposite sign of the control signal during the second half-period of the control signal, shifted by 270°. The same occurs with control signals b and c, only with a phase shift of 120° and 240°, respectively.

[0040] The time or period for changing the switching state is phase-shifted accordingly, so that the change is made in the middle of a plateau of the respective control signal and symmetrically to it.

[0041] This controls the voltage-time area of ​​the voltages and thus the output of the DC-DC converter.

[0042] At a slope of 60°, all control signals are superimposed, meaning switches S1 to S6 are switched synchronously. With a slope between 60° and 0°, the output voltage Uout can be regulated to a setpoint between 0V and a maximum voltage value. Surprisingly, there is a linear relationship between the slope as the controlled variable and the voltage-time area applied to the transformer input, which is the variable being controlled. This is particularly advantageous in digital control systems.

[0043] Advantageously, a control system will only change the voltage component after a full 360° cycle, thus avoiding a DC component. This could otherwise lead to saturation of the transformer and therefore at least weaken power transmission.

[0044] The voltages U1, U2, and U3 generated by inverter 1 at the primary windings of transformer 16 are transferred by transformer 16 to its three secondary windings. Each of the three secondary windings is connected to a rectifier. The outputs of the rectifiers are connected in a star configuration to the output of the DC-DC converter, thus forming the output voltage Uout.

[0045] Advantageously, the rectifiers are designed as center-tap rectifiers. With a center-tap on each of the three secondary windings, only two switching elements or diodes are required to rectify the voltage.

[0046] At the in Fig. In the embodiment shown in 1, the center-tap rectifiers each have two switches S7 to S12. These are controlled accordingly to rectify the alternating voltage provided by the secondary windings.

[0047] The use of switches has the advantage that it also allows energy to be fed back from the output side of the DC-DC converter to the input side. For this purpose, switches S7 to S8 are controlled synchronously in conjunction with the inverter switches on the primary side of the transformer.

[0048] The center tap of each secondary winding is connected to the output of the DC-DC converter via an inductor 28. For further smoothing of the output voltage, the following applies to the Fig. 1 shown embodiment of each

[0049] The rectifier includes a capacitor 26 arranged in parallel to the output of the DC-DC converter.

[0050] In another embodiment, the switches are replaced by diodes, with the anodes of the diodes being connected to an external tap of the respective secondary coil and the cathodes being grounded.

[0051] The three-phase DC-DC converter allows the windings of transformer 16 to be wound onto a three-legged core of the transformer. This ensures optimal utilization of the core material.

[0052] The DC-DC converter according to the invention allows for simple and rapid control of the output voltage to compensate for fluctuations in the input voltages or load changes on the output side. A simple setpoint of the component is sufficient for this purpose. By using a three-phase system with a three-phase transformer as transformer 16, the output voltage, or rather the ripple of the output voltage, has a frequency close to the clock frequency.

[0053] The DC / DC converter is preferably designed as a forward-flow converter. Reference symbol list 1 inverter 10 first half-bridge 12 second half-bridge 14 third half-bridge 16 Transformer 18 first rectifier 20 second rectifier 22 third rectifier 24 Input capacitor 26 Capacitor 28 Inductance

Claims

[1] Method for operating a controlled three-phase DC-DC converter, wherein three AC voltage phases are generated from an input voltage of the DC voltage converter by means of an inverter (1) with three half-bridges (10, 12, 14), wherein the three half-bridges (10, 12, 14) are controlled by a respective periodic control signal, in particular to generate a desired control output, which alternates between two control states, wherein the periodic control signals are each phase-shifted by 1 / 3 of a period relative to each other and, when the DC-DC converter is fully driven, the periodic control signals within each period correspond to a step function with one step after each half-period, wherein, to change the output of the DC-DC converter for each input phase within a respective half-period, the control state is switched symmetrically in the middle of the respective half-period for a portion of the respective half-period, in particular, where, therefore, the proportion disappears when the control is fully activated. where a transformer (16) in a delta connection is connected to the three half-bridges (10, 12, 14), wherein the AC voltage phases are connected to a respective phase of a transformer in a delta connection and the transformer converts the three AC voltage phases into three output phases, wherein a rectifier rectifies the converted alternating voltage, the rectified, converted alternating voltage then forms the output voltage of the DC-DC converter. [2] Method according to claim 1 characterized bythat the proportion of the half-period is the same for each input phase. [3] Method according to claim 1 or 2, characterized by , that the proportion of the half-period of 180 degrees lies between 0 degrees and 60 degrees. [4] Method according to any one of claims 1 to 3 characterized by , that the voltage of the alternating voltage phases is generated by switching two switches of the half-bridges (10, 12, 14), In particular, the half-bridges (10, 12, 14) feature a range circuit which is supplied by the input voltage, with two switches each. [5] Method according to claim 4 characterized by , that the voltage states are changed by either closing an upper switch of a half-bridge (10, 12, 14) and opening a lower switch or vice versa. [6] Method according to any of the preceding claims characterized by that the initial phases are each aligned. [7] Method according to any of the preceding claims characterized by , that the three output phases are each rectified by a rectifier circuit and combined in parallel as one output voltage of the DC-DC converter. [8] Method according to claim 7, characterized by , that each rectifier circuit has two switches which are timed accordingly to rectify the output phases. [9] Method according to claim 8 or 7, characterized by , that the voltages of the rectified output phases are smoothed with a capacitor (26) each. [10] Method according to any of the preceding claims characterized by , that the switches of the rectifier circuits are operated in such a synchronized manner with the switches of the inverter (1) that a feedback, i.e. an energy flow from the output side to the input side of the DC voltage converter, is carried out. [11] Arrangement with an electrical circuit, characterized by that the electrical circuit for carrying out the steps of the method of one of the preceding claims is set up. [12] Arrangement according to claim 11, characterized by , that the primary windings and secondary windings of the transformer (16) are wound on a three-legged core of the transformer (16). [13] Arrangement according to claim 12 or 11, characterized by , that a center-point rectifier is arranged on the secondary side at the secondary winding, which rectifies the transformer output voltage. [14] Arrangement according to claim 12, 13 or 11, characterized by , that an inductor (28) is connected in series and / or a capacitor is connected in parallel to the output before the output of the DC voltage converter.

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