WO2017028988A1

WO2017028988A1 - Three-phase dc converter

Info

Publication number: WO2017028988A1
Application number: PCT/EP2016/063979
Authority: WO
Inventors: Emiliano GUDINO CARRIZALES
Original assignee: Robert Bosch Gmbh
Priority date: 2015-08-20
Filing date: 2016-06-17
Publication date: 2017-02-23
Also published as: DE102015215869A1

Abstract

The invention relates to a three-phase D,C converter comprising a pair of input terminals (U₁) for an input DC voltage, a pair of output terminals (U₂ for an output DC voltage, a three-phase transformer (1) comprising at least three limbs, each of the limbs being surrounded by at least one primary winding (U, V, W) and a secondary winding (u, v, w), which are led in planar technology as conductor tracks on the substrate around the associated limb, and wherein common yokes complete the magnetic circuits via the respective other limbs, an electronic control device (5), which is designed to activate a multiplicity of electronic switches periodically, depending on the electric power output on the output terminals (U₂), three pairs of electronic input switches (11, 11'; 12, 12'; 13, 13'), which connect the input terminals (U₁) to the primary windings (U, V, W) in such a way that, controlled by the control device (5), respectively one connection of each of the three primary windings (U, V, W) can be connected to the positive pole or to the negative pole of the input connections (U₁), three pairs of output switches (14, 14'; 15, 15'; 16, 16'), which connect the output terminals (U₂) via a filter (6, 6') to the secondary windings (U, V, W), in such a way that, controlled by the control device (5), respectively one terminal of each of the three secondary windings (u, v, w) can be connected to the positive pole or to the negative pole of the output terminals (U₂), wherein the filter (6,6') is designed to smooth ripple of the power output on the output terminal (U₂).

Description

description

title

Three-phase DC-DC converter

The invention relates to a three-phase DC-DC converter with a three-phase transformer and electronic switches, which are switched by an electronic control device.

State of the art

DC-DC converters serve to transfer current from a DC voltage source having a voltage at input terminals Ui to a level having another - higher, equal to or lower - voltage at output terminals U ₂ and to operate loads at that voltage. The design of such a converter depends on the requirements that are addressed to it. In addition to the height of the voltages at the terminals Ui and U ₂ , these include, in particular, the type and magnitude of the load, in particular the maximum permissible load, the time profile of the load and the desired efficiency in partial and full load operation. There are more besides

Requirements, e.g. the dissipation of heat loss, the electromagnetic radiation to the environment and the mechanical robustness.

Especially for use in electric and hybrid vehicles, there is a need for converters that transform from a high-voltage network (typically: 400 V) to a low-voltage network (typically: 12 V). Often, a converter with a single-phase transformer is used, which ensures the galvanic isolation between high and low voltage network, which is important for the safety of the user. The transformer is on the primary side with electronic Switches equipped in bridge circuits, ie each of the two terminals of the primary coil can be connected via a switch to the positive terminal or to the negative terminal of the input terminals Ui. With these switches, the primary coil of the transformer can be periodically applied with the voltage at the input terminals Ui with alternating polarity, ie with rectangular voltage pulses. This results in the duration of such a pulse, a constant increase in current in the transformer, which changes its direction depending on the polarity. According to the law of induction thereby a constant during the pulse voltage is generated in the secondary circuit, ie there are also there rectangular voltage pulses. The amount of voltage is determined by the ratio of the turns of the primary and secondary windings. If switches are used on the secondary side, the secondary winding is reversed by means of these switches with the same timing as the primary current, whereby the same constant voltage is always output on the output side.

In the partial load range, such a converter for a part of the period

are switched off, so that at the input terminals Ui no power is removed. There are various ways of switching the switches. In a phase-shifted switching ("Phase Shifted") for the two junctions of the transformer primary coil are not exactly in push-pull (180 ° phase shift) simultaneously connected to the other pole of the battery, but the polarity reversal of the second connection takes place only with a predetermined Phase shift with respect to the first terminal, thereby shorting the primary coil of the transformer for a portion of the period while simultaneously having one pole of the input voltage

is disconnected, so that at this time the primary network no performance

is removed. The magnitude of the phase shift requires control by measuring the power dissipated in the secondary network and the

Phase shift is adjusted accordingly, so that exactly the required power is delivered to the output terminals U ₂ . Because of the

Bridge switching of the switch, this type of control is referred to as "Fill Bridge Phase Shifted" (FBPS). On the secondary side, diodes can be used as rectifiers, or electronic switches, which can then be synchronized with the switches in the

Primary circuit can be switched. An alternative power control is that the time within each period during which the input terminals Ui are connected to the primary winding is less than the maximum possible duration (each half a period). Also in this case are the

Primary windings for the remainder of the period separated from the DC voltage source, so that no power is delivered. This type of control is referred to as pulse width modulation (PWM).

In such a converter, the operating frequency can be chosen so that the losses are minimized at full load. Part of the losses, especially in the transformer, are the higher, the lower the clock frequency. For the longer the current increases until the next polarity change, and the higher the current and thus the magnetic flux in the transformer, since both sizes are lossy. Other contributions to the losses, especially the switching losses at the electronic switches, increase with increasing switching frequency. Because the switches have both in the open state because of the current zero through the switch, as well as in the closed state because of the voltage drop zero at the switch, only small losses. However, at the moment of switching, which takes a finite time, the losses may become non-zero, if at this time the power at turn-off or the voltage at power up is not equal to zero. This switching is also called "hard switching." To minimize these losses, low-loss "soft switching" is sought, that is, at a moment when the current or voltage is near zero. The resulting optimum switching frequency can be from a few 10 kHz up to several 100 kHz and must be optimized for each individual case of the design of the converter.

The transformers that are used for DC-DC converters can be conventionally designed as a wound component or in planar technology. In the latter case, the coils can be applied as printed conductors on a circuit board, which are around recesses in the board around run. The transformer cores with the yokes are then attached to the

Cutouts - one part each from both sides - mounted on the board. This planar technology has not only cost advantages in mass production, but at high frequencies also benefits in terms of skin effect.

If the requirements for DC-DC converters increase with regard to the power delivered, several of them can be connected in parallel. If these are phase shifted to each other ("interleaved"), then a higher efficiency can be achieved than with a single converter, which is designed for the higher power.However, with the number of converters and the number of components for the circuit.

In this context, EP 1 589 648 A2 proposes a

To use three-phase converter, which uses a transformer that is constructed like a three-phase transformer with three primary and three secondary windings. This reduces the losses and also the emission of harmonics.

WO 2006/027744 A2 proposes in addition to this, two such

Transformers in parallel and out of phase with each other

To operate ("interleaved").

DISCLOSURE OF THE INVENTION The invention has a three-phase DC-DC converter for

An article having a pair of input terminals for an input DC voltage and a pair of output terminals for an output DC voltage, and a three-phase transformer comprising at least three legs, each of the legs being surrounded by at least one primary winding and one secondary winding. These windings can be designed in planar technology as conductor tracks on a substrate. For example, the one winding may be guided on the upper side and the other on the underside of the substrate about the associated leg. Common yokes can close the magnetic circles over the other thighs. The advantage of using a three-phase transformer is that, with the same output power, fewer components are required in comparison with several parallel-operated single-phase converters, and the magnetic load on the transformer legs is lower. It will be advantageous way, in particular less switch, transformer windings and -schenke! and output inductors, as well as MOSFET and IGBT drivers and their components needed.

The three-phase DC-DC converter has three pairs of electronic input switches, which are connected to the input terminals and - possibly via an inductance - to the primary windings, that in each case a connection of each of the three primary windings of the transformer, depending on

Switch position, can be connected to the positive pole or to the negative pole of the input voltage.

In addition, the three-phase DC-DC converter can use three pairs of

Output switches having, in such a way with the secondary windings and - possibly via a screen member - are connected to the output terminals, that in each case one terminal of each of the three secondary windings can be connected to the positive pole or to the negative terminal of the output voltage.

In addition, the three-phase DC-DC converter may comprise an electronic control device, which is designed to periodically control a plurality of electronic switches in dependence on the electrical power to be output at the output terminals.

The screen member is designed to smooth ripples of the power delivered to the output terminal due to the fact that the converter outputs power to the output only part of each period depending on the load. For example, it consists of a coil and a

Capacitor.

The wiring of the respective other ends of the three primary windings and the three secondary windings is possible in different embodiments of the invention and is referred to as the architecture of the circuit. The three connections of the three primary windings can be connected together to form a neutral point. Alternatively, each of these terminals may be connected to the terminal connected to a pair of the input switches of one of the other two primary windings, such that the

Primary windings are interconnected to form a triangular arrangement.

Likewise, the three terminals of the secondary windings can become one

Star point can be interconnected. Alternatively, each of these terminals may be connected to the one connected to a pair of the output switches

Connection of one of the other two secondary windings be connected, such that the secondary windings are interconnected to form a triangular arrangement.

The star-shaped circuit is denoted by Y, the triangular by D. Accordingly, embodiments of the invention may have a YD, a DY, a YY or a DD architecture.

In the star connection (Y-circuit) is advantageous that each reduces the winding voltage of the transformer, while the advantage of the delta connection (D circuit) in reducing the current through the

Transformer windings lies. Both reduce the magnetic load of the legs compared to a combination of three single-phase transducers of the same transmittable power and thus leads to a higher efficiency.

The control device can also be realized in different embodiments of the invention. In a first embodiment, it may e.g. be designed to be periodically operated at a frequency such that the steady state resonant circuits formed by the inductances in the primary circuit and the parasitic capacitances of the electronic input switches have current and voltage resonant circuits and then connecting and disconnecting the primary windings

Input terminals resonantly takes place at these zeros. This advantageously reduces the switching losses of the electronic switches. That's it Furthermore, it is advantageous if the design of the transformer is such that no additional resonant inductances are required as additional components, but if these are integrated in the transformer windings. In this embodiment of the invention, the control device may be designed such that the connection of the secondary windings with the

Output terminals are made at the same times as connecting the primary windings to the input terminals, and that the separation of the secondary windings from the output terminals is determined by a signal for the level of the load. As a result, the switching losses are limited in an advantageous manner to the turn-off of the switches in the secondary circuit.

In a further embodiment of the invention but also the time of disconnecting the connection of the primary windings of the

Input voltage to be determined by the height of the load, wherein connecting and disconnecting the connection of the secondary windings with the

Output terminals simultaneously with connecting and disconnecting the

Connection of the primary windings with the input voltage takes place. As a result, the switching losses are limited in an advantageous manner to the turn-off of the switches in the primary circuit.

In a further embodiment of the invention, the electronic control device has a microprocessor and is designed such that the actuation of the electronic switch is predetermined by the software controlling the microprocessor. This advantageously allows a simple adaptation of the converter as the requirements change.

In a further embodiment variant of the invention, the control device can be designed in such a way that the transformer frequency is threefold

Switching frequency of the input switch is and which is connected to the

Output terminals forming ripples have six times the frequency. This advantageously reduces the maximum current in the transformer and the size of the ripple.

Another advantage of the invention is that the converter because of its symmetrical structure when needed and appropriate control of Switch can also transmit electrical power in the reverse direction, ie from the output terminals to the input terminals Ui.

Brief description of the drawings

The invention will be explained in more detail with reference to the drawings. FIG. 1

shows the basic circuit of a three-phase DC-DC converter according to an embodiment of the invention.

FIG. 2

shows the basic structure of a three-phase transformer, as it can be used in an embodiment of the invention.

FIG. 3

shows the wiring of a three-phase transformer, as it can be used in an embodiment of the invention with DY architecture.

FIG. 4

shows the wiring of a three-phase transformer, as it can be used in an embodiment of the invention with YD architecture.

FIG. 5

shows the wiring of a three-phase transformer, as it can be used in an embodiment of the invention with DD architecture.

FIG. 6

shows the wiring of a three-phase transformer, as it can be used in an embodiment of the invention with YY architecture.

Figure 1 shows the basic structure of a three-phase

DC-DC converter, which receives at the input terminals Ui electrical power from an input DC voltage source, such as a battery, and this electrical power to output terminals U ₂ as Output DC voltage to an output network. Often, the voltage at the output is smaller than that at the input, but it can also be greater than or equal to the voltage at the input.

In the center of the circuit is a three-phase transformer 1, for the figure 2 shows an embodiment. It comprises at least three legs 2, 2 'and 2 ", each of the legs being surrounded by at least one primary winding U, V and W and a secondary winding u, v and W. These windings are in the figure in planar technology as printed conductors on a substrate 3, which are guided around the associated limb, wherein the figure shows only a single turn for the sake of clarity, the ratio of the number of turns from primary turns to secondary turns determines the ratio of the output voltage to the input voltage The magnetic flux circuits of the three limbs 2, 2 ' and 2 "are closed via the respective other legs by common yokes 4 and 4 '.

As FIG. 1 shows, the DC-DC converter can have twelve electronic switches, which are actuated by an electronic control device 5. Of these switches, two are each connected to one end of the six windings of the transformer. Via the switches 11, 11 ', 12, 12', 13 and 13 ', these winding ends of the primary windings - in each case via a resonance inductance 17, 17' and 17 "- can be connected to the positive pole or to the negative pole of the input terminals Ui, and Via the switches 14, 14 ', 15, 15', 16 and 16 ', the winding ends of the secondary windings can be connected via a common filter element - eg with an inductor 6 and a capacitor 6' to the positive pole or to the negative pole of the output terminals U ₂ become.

The control device 5 is designed to periodically switch these switches on and off as a function of the electrical power output at the output terminals U ₂ such that each of the three primary windings U, V and W has its one end temporarily connected to the positive pole or to the negative pole the input terminals Ui is connected, without that in the meantime the

Input voltage is shorted, and also that each of the three secondary windings u, v and w with its one end temporarily with the positive pole or is connected to the negative pole of the output terminals U ₂ , without in the meantime the output terminals are short-circuited.

The wiring of the respective other ends of the three primary windings U, V and W and the three secondary windings u, v and w is in different

Embodiments of the invention illustrated in Figures 3 to 6 and is referred to as the architecture of the circuit.

The three terminals of the three primary windings U, V and W can be interconnected to form a neutral point 17 (compare FIGS. 4 and 6). Alternatively, each of these terminals may be connected to the terminal connected to a pair of the input switches of one of the other two primary windings, such that the three primary windings are connected together in a triangular arrangement (see Figures 3 and 5).

Likewise, the three terminals of the three secondary windings u, v and w can be connected together to form a neutral point 18 (compare FIGS. 3 and 6). Alternatively, each of these connections with the - with a pair of

Output switch connected - be connected connection of one of the other two secondary windings, such that the three secondary windings are interconnected to form a triangular arrangement (see Figures 4 and 5).

The primary circuit, in one embodiment, includes inductors, which may include particular resonant inductances 17, 17 'and 17 "that are supplemented for matching purposes, and parasitic capacitances such as the input switches 11, 11', 12, 12 ', 13 and 13 The control means 5 may then be designed and periodically operated at a frequency such that these steady state resonant circuits have zero current and voltage, and connecting and disconnecting Primary windings U, V, W with the input terminals Ui are resonant at these zeroes, namely the zero voltage connection and the zero current isolation. The primary circuit is thus "soft" switched on and off in this type of control.

In this embodiment, connecting the secondary windings u, v and w to the output terminals U ₂ at the same times as that

Only the secondary windings u, v, w are disconnected from the output terminals U ₂ as a function of a signal 7 for the height of the load and is therefore "hard". In this case, this signal 7 by the averaged product of

Output voltage with the voltage drop across a measuring resistor (as a measure of the given current) are formed.

In another embodiment of the invention, the control device 5 is designed such that the time of disconnecting the connection of the primary windings U, V, W from the input terminals Ui is determined by the height of the load corresponding to the signal 7 and therefore "hard" occurs, and wherein the connection and disconnection of the connection of the secondary windings u, v and w with the output terminals U _{2 can take place} simultaneously with the connection and disconnection of the primary windings U, V and W with the input terminals Ui and thus "soft". This mode is referred to as PWM (Pulse Width Modulation).

The control device 5 may have a microprocessor and be designed such that the actuation of the electronic switches is predetermined by the software controlling the microprocessor.

The control device 5 can be designed so that the

Transformer frequency of the transformer 1, the triple switching frequency of the input switches 11, 11 '; 12, 12 '; 13, 13 'amounts to and to the

Output terminals U ₂ forming ripples have six times the frequency. With the level of this frequency, the length of the time duration during which, given a given load, the transformer does not give off any current and the output must be supplied from the energy stored in the sieve member 6 and 6 ', the output voltage drops slightly. This also reduces the amplitude of the ripples.

Claims

Expectations

1. Three-phase DC-DC converter, comprising:

• a pair of input terminals (Ui) for an input DC voltage,

• a pair of output connections (U ₂ ) for an output direct voltage,

• a three-phase transformer (1), comprising at least three legs (2, 2',

2"), each of the legs being surrounded by at least one primary winding (U, V, W) and one secondary winding (u, v, w), which are used in planar technology as conductor tracks on a substrate

(3) are guided around the associated leg, and with common yokes (4,

4') close the magnetic circuits over the other legs,

• an electronic control device (5) which is designed to control a plurality of electronic switches (11, 11'; 12, 12'; 13, 13'; 14, 14'; 15, 15'; 16, 16'). Dependence on the

to periodically control the electrical power delivered from the output connections (U ₂ ),

• three pairs of electronic input switches (11, 11'; 12, 12'; 13, 13'), which connect the input connections (Ui) with the

Connect primary windings (U, V, W) so that, controlled by the control device (5), one connection of each of the three primary windings (U, V, W) can be connected to the positive pole or to the negative pole of the input connections (Ui),

• three pairs of output switches (14, 14'; 15, 15'; 16, 16'), which thus connect the output connections (U ₂ ) to the secondary windings (u, v, w) via a filter element (6, 6'). that, controlled by the control device

(5), one connection of each of the three secondary windings (u, v, w) can be connected to the positive pole or to the negative pole of the output connections (U ₂ ),

• where the sieve element (6,

6') is designed to have ripples on the

Output connection (U ₂ ) to smooth output power. Three-phase DC-DC converter according to claim 1, wherein the other ends of the three primary windings (U, V, W) are connected together to form a star point (17).

A three-phase DC-DC converter according to claim 1, wherein the other ends of the three primary windings (U, V, W) are connected to the terminal of another winding connected to a pair of the input switches (11, 11'; 12, 12'; 13, 13'). is, such that the primary windings (U, V, W) are connected together to form a triangular arrangement.

Three-phase DC-DC converter according to claim 2 or 3, wherein the other ends of the three secondary windings (u, v, w) are connected together to form a star point (18) (YY or DY circuit).

A three-phase DC-DC converter according to claim 2 or 3, wherein the other ends of the three secondary windings (u, v, w) are each connected to the terminal connected to a pair of the output switches (14, 14'; 15, 15'; 16, 16'). is connected to another winding, such that the

Secondary windings (u, v, w) are connected together to form a triangular arrangement (YD or DD circuit).

Three-phase DC-DC converter according to one of claims 2 to 5, wherein the control device (5) is designed and is periodically operated at such a frequency,

• that the resonance circuits formed from the inductances (U, V, W, 17, 17', 17") in the primary circuit and from the parasitic capacitances of the input switches (11, 11'; 12, 12'; 13, 13') in the stationary circuit Operation have zero points for current and voltage and the connection and disconnection of the primary windings (U, V, W) with the input connections (Ui) takes place resonantly at these zero points,

• that connecting the secondary windings (u, v, w) to the

Output connections (U ₂ ) occur at the same times, • and that the separation of the secondary windings (u, v, w) from the output connections (U ₂ ) is determined by a signal (7) for the height of the load.

7. Three-phase DC-DC converter according to one of claims 1 to 5, wherein the control device (5) is designed such that the time of disconnection of the primary windings (U, V, W) with the

Input connections (Ui) is determined by the level of the load, and the connection and disconnection of the secondary windings (u, v, w) with the output connections (U ₂ ) simultaneously with the connection and disconnection of the primary windings (U, V , W) with the

input connections (Ui).

8. Three-phase DC-DC converter according to one of claims 1 to 7, wherein the control device (5) has a microprocessor and is designed such that the actuation of the electronic switches (11, 11 '; 12, 12'; 13, 13'; 14, 14'; 15, 15'; 16, 16') is specified by the software controlling the microprocessor.

9. Three-phase DC-DC converter according to one of claims 1 to 8, wherein the control device (5) is designed so that the

Transformer frequency is three times the switching frequency of the input switches (11, 11'; 12, 12'; 13, 13') and the ripples forming at the output connections (U ₂ ) have six times the frequency.