3-phase rectifier circuit with push-pull transformers and reduced transistor effort

Abstract

The invention relates to a transistor-effective circuit (1) having • a primary side (P) for three phases (L1, L2, L3), having at least two semiconductor switches (T1, T2), • wherein on the primary side (P) during operation, a first switched-on state (a) and a second switched-on state (c) are provided in addition to a switched-off state (b), wherein during operation, a further switched-off state follows the first switched-on state (a), wherein during operation, a switched-off state follows the second switched-on state (c), • a secondary side (S) for a controlled voltage output having at least one semiconductor switch (T3…T8), • wherein switching phases on the secondary side (S) are dependent on there being a switched-on state on the primary side (P), wherein during operation, an input-side alternating voltage (Uin) is converted into a settable output voltage (Uout).

Description

[0001] 3-PHASE RECTIFIER CIRCUIT WITH PUSH-PULL TRANSFORMERS AND REDUCED TRANSISTOR EFFORT

[0002] background

[0003] Direct current is required in many electrical energy applications. However, the majority of transmission grids are based on alternating current (AC) networks. Three-phase AC networks are particularly popular.

[0004] However, DC voltage is often required by electrical consumers. Examples of DC voltage consumers include electrolyzers, battery storage systems, LED lighting, etc.

[0005] This DC voltage usually has a different voltage level than the voltage provided by the AC grid. The required voltage often also varies.

[0006] With regard to safety, there is often a desire and sometimes a requirement to provide galvanic isolation.

[0007] In the past, a single-phase alternating current was typically provided with a rectifier. A variety of circuits exist for this purpose.

[0008] However, if a three-phase current network, i.e. a three-phase alternating current network, is used as the source, an adjustable output voltage - and in particular an adjustable direct voltage - is only possible in the prior art with great effort using a large number of, for example, 14 or more semiconductor switches - see also EP 2 599 207 B1 by the inventor, or - with fewer semiconductor switches - only with poor properties, such as efficiency or available power. With the number of semiconductor switches, not only do the costs rise directly due to the comparatively expensive semiconductor switches, but the complexity of the control system, the need for compensation networks, etc. also leads to an increase in the costs for the development, construction and operation of such devices. Furthermore, circuits with a large number of components tend to be unreliable.

[0009] Based on this, it is an object of the invention to provide a transistor-effective circuit which allows an adjustable output voltage to be provided when supplied from a three-phase AC voltage network.

[0010] The object is achieved by a transistor-effective circuit according to claim 1. Further advantageous embodiments are the subject matter in particular of the dependent claims, the description and the figures.

[0011] The invention is explained in more detail below with reference to the figures, which show:

[0012] Fig. 1: a schematic rough representation of a circuit according to an embodiment of the invention, indicating the time course of the current of an input phase on the mains side i ac , primary side i, secondary side i ou t and output side idc,

[0013] Fig. 2: a schematic rough representation of the primary side according to embodiments of the

[0014] Invention,

[0015] Fig. 3a-c schematic representations of possible configurations of primary-side semiconductor switches according to embodiments of the invention, and

[0016] Fig. 4a-e schematic representations of possible configurations of secondary sides according to embodiments of the invention.

[0017] Detailed Description of the Invention The invention will be described in more detail below with reference to the figures. It should be noted that various aspects are described, each of which can be used individually or in combination. This means that any aspect can be used with different embodiments of the invention, unless explicitly presented as a mere alternative.

[0018] Furthermore, for the sake of simplicity, reference will generally be made to only one entity in the following. Unless explicitly stated, the invention may also comprise several of the entities in question. Therefore, the use of the words "a," "an," and "another" is to be understood merely as an indication that at least one entity is used in a simple embodiment.

[0019] Where procedures are described below, the individual steps of a procedure can be arranged and / or combined in any order, unless the context explicitly indicates otherwise. Furthermore, the procedures can be combined with one another, unless expressly indicated otherwise.

[0020] Numerical values ​​are generally not to be understood as exact values, but also include a tolerance of + / - 1% to + / - 10%.

[0021] References to standards or specifications are to be understood as references to standards or specifications that are / were in effect at the time of the application and / or, if priority is claimed, at the time of the priority application. However, this does not imply a general exclusion of applicability to subsequent or replacing standards or specifications.

[0022] Embodiments of the invention are explained below with reference to the figures. It should be noted in advance that, within the scope of the invention, any configuration of a primary side configured according to Figures 2 and 3a-c can be combined with any configuration of a secondary side configured according to Figures 4a-e.

[0023] In all embodiments of the invention, a transistor-effective circuit 1 is provided.

[0024] Each of these embodiments of the invention has a primary side P for three phases LI, L2, L3 of a three-phase AC voltage network.

[0025] Each of these primary sides P has - as shown in Figure 2 - at least two semiconductor switches TI, T2.

[0026] During operation, in addition to an off state b, a first on state a and a second on state c are provided on the primary side P. The first on state a can be provided, for example, by the first semiconductor switch TI being switched on and conducting, while the second semiconductor switch T2 is switched off and correspondingly blocks. The second on state c can be provided, for example, by the second semiconductor switch T2 being switched on and conducting, while the first semiconductor switch TI is switched off and correspondingly blocks. The off state b can be provided, for example, by both the first semiconductor switch TI and the second semiconductor switch T2 being switched off and correspondingly blocks.

[0027] During operation, a first switched-on state—e.g., state a—is followed by an off state—e.g., state b. The off state can then be followed by another switched-on state; e.g., the second switched-on state c follows the off state b. This means that a switching state in which both semiconductor switches T1, T2 are switched on is not provided.

[0028] Each of these embodiments of the invention has a secondary side S for a regulated voltage output. For example, each of the secondary sides S has at least one semiconductor switch T3,...T8. However, as can be seen from Figures 4a-4e, more or fewer semiconductor switches T3...T8 can also be present.

[0029] In all embodiments of the invention, the primary side P and the secondary side S can be galvanically separated.

[0030] In all embodiments of the invention, ie in particular all circuits of the secondary side according to Figures 4a-4e, the switching phases of the semiconductor switch T3 or the semiconductor switches T3....T8 on the secondary side S are dependent on the fact that on the primary side P a switched-on state, ie a switched-on state a or a switched-on state c, is present, wherein then during operation an input-side alternating voltage U into an adjustable output voltage U ou t is transferred.

[0031] This means that the invention enables the provision of a pulse rectifier which provides a (galvanically isolated) DC output voltage of selectable magnitude while simultaneously providing a sinusoidal mains current consumption.

[0032] Unlike many previously used circuits, frequency components of both the mains frequency and the switching frequency of the primary side are present in the transformers Trl...Tr3.

[0033] For this purpose, at least two turn-off semiconductor switches TI and T2 are required on the primary side and at least one turn-off semiconductor switch T3 on the secondary side.

[0034] Thus, a transistor-effective circuit can be provided in a particularly cost-effective manner, which allows an adjustable output voltage to be provided when supplied from a three-phase supply network using only a few semiconductor switches and a simple control system.

[0035] To illustrate the functional principle, reference is made to Figure 1, which shows a circuit configuration of the primary side according to Figures 2 and 3a, and the secondary side according to Figure 4c. In general, a pulse rectifier based on the invention can be provided by a three-phase, symmetrical circuit comprising two semiconductor switches TI and T2 on the primary side, three transformers Tri, Tr2, and Tr3, each with a split primary winding, and one secondary part per phase (a secondary part can also have multiple windings).

[0036] As already known from Japanese patent application JP-A-2000 014 157, the two primary-side switches TI, T2 serve to connect the corresponding outputs of the primary windings of the three transformers Tri, Tr2, Tr3. This creates a three-phase voltage system across the corresponding primary windings, which then appears on the secondary side. The primary-side switches TI, T2 are switched alternately - as already described - so that the switching states a, b, and c are realized.

[0037] However, in the Japanese laid-open specification JP JP-A- 2000 014 157, the uncontrolled bridge connected on the secondary side and the smoothing inductance do not result in a sinusoidal current waveform.

[0038] In the present invention, this is different. Here, the secondary-side, pulsed, and polarity-alternating transformer voltages per phase can be fed via two diodes each to a secondary-side component, which in Figures 1 and 5c is designed, for example, as a boost converter in continuous operation. Furthermore, the three secondary-side components can, for example, have a common ground, so that they can operate via the three boost diodes D13, D23, and D33 on a common capacitor C (Fig. 4c).

[0039] The secondary-side switching frequency of T3 to T8 can be selected to be much higher than the primary-side switching frequency of T1 and T2. Unlike in the prior art, switching / switching occurs depending on the switching state of the primary side. Thus, switching / switching of the semiconductor switches T3...T8 of the secondary side S can be performed in such a way that this preferably only occurs while the primary side is switched on, i.e., switching states a and c. The semiconductor switches T3...T8 of the secondary side S should not be switched on while the primary side is switched off, and ideally, this is completely avoided.

[0040] In front of the coil LI, U is now created T3 a sequence of nearly rectangular voltage blocks with a rectified mains-frequency sine wave as the envelope. Within these voltage blocks, the current through coil LI can be controlled with the help of the boost converter formed by LI, T3, and D13 so that it is also nearly block-shaped and proportional to the currently applied mains voltage (i.e., corresponding to one of the switched phases LI, L2, L3). The two other secondary-side sections belonging to the other phases can be controlled in the same way.

[0041] In this way, the mains current i is designed and controlled on the input side according to the invention. ac almost sinusoidal and on the output side an adjustable DC voltage Ua is provided, the level of which can be selected by the transformation ratio of the transformer.

[0042] According to one embodiment of the invention, the switching frequency of the primary side P relating to the semiconductor switches TI, T2 is more than 9 times a mains frequency applied on the primary side.

[0043] According to a further embodiment of the invention, the switching frequency of the secondary side S concerning the semiconductor switches T3...T8 is more than 4 times the switching frequency of the primary side P.

[0044] In one embodiment of the invention - see for example Figure 1 - the circuit has fewer than 14 transistors.

[0045] It is particularly advantageous that, in embodiments of the invention, it is possible for the circuit to provide currentless switching on the primary side P. Furthermore, in embodiments of the invention, it is possible for the transistors T1...T8 to comprise silicon carbide transistors or gallium nitride transistors or super junction MOSFET transistors or IGBT transistors.

[0046] As can be seen from Figures 4a-4d, in embodiments of the invention, the output voltage can be a regulated direct current voltage. However, in alternative embodiments of the invention—as can be seen from Figure 4e—the output voltage can also be a regulated alternating current voltage.

[0047] topology

[0048] The transistor-effective circuit 1 can be divided into a primary side P and a secondary side S, as can be seen from the combined view of the figures. Optionally, a low-pass filter can also be arranged on the primary side facing the mains.

[0049] Below, different exemplary options for the primary side P and the secondary side S are described, which can be operated together in all variants without restriction.

[0050] Primary page

[0051] The primary side P in its various exemplary and non-limiting embodiments is the subject of Figures 2 and 3a-3c.

[0052] Figure 2 shows the primary sides of the transformers Tri, Tr2, and Tr3. The windings are counter-rotating, as indicated in Figure 2. The transformer windings are controlled by the three phases LI, L2, L3. Two semiconductor switches TI, T2 are arranged on the primary side. The other sides of the primary windings of the transformers Tri, Tr2, and Tr3 are each connected to one of the two semiconductor switches TI, T2. The semiconductor switches TI, T2 can be designed as shown in Figures 3a-3c by way of example but not by way of limitation. The semiconductor switches TI, T2 have a dielectric strength that corresponds to at least twice the peak voltage of a phase LI, L2, L3.

[0053] Figure 3a shows an example of a semiconductor switch TI, T2. If this is installed as shown in Figure 2, the three outputs A1, A2, A3 of the primary windings each form the inputs of an uncontrolled bridge, the DC taps of which can be bridged using semiconductor switches. This circuit represents a cost-effective variant, as only two semiconductor switches are required (one each in TI and T2). Figure 3b shows a further example of a semiconductor switch TI, T2. Direct short-circuiting can be achieved using a turn-off and reverse-conducting semiconductor switch connected between each phase. This circuit combines cost-effectiveness with improved efficiency, as the conduction losses are lower than in the circuit shown in Figure 3a.It should be noted that the semiconductor switches shown in Figure 3b in a star arrangement can also be connected analogously as a delta (with appropriate selection of the semiconductor switches).

[0054] Figure 3c shows another example of a semiconductor switch T1, T2. The three outputs of the primary windings form the inputs A1, A2, and A3 of a fully controlled three-phase bridge. Unlike the variant shown in Figure 3b, this circuit allows for a reduced load per semiconductor switch. This allows for the use of more cost-effective semiconductor switches.

[0055] Secondary side The secondary side S in its various exemplary and non-limiting configurations is the subject of Figures 5a-e. Unlike on the primary side P, no corresponding requirements apply to the dielectric strength of the semiconductor switches T3...T8 on the secondary side S.

[0056] In the secondary side shown in Figure 4a, only one of the three phases is shown. The other phases can be configured similarly. This circuit is particularly efficient when using GaN transistors as semiconductor switches T3...T6.

[0057] In the secondary side shown in Figure 4b, unlike the circuit in Figure 4a, only a single-phase output voltage U a This circuit is also particularly efficient.

[0058] The circuit shown in Figure 4c requires only 3 semiconductor switches T3...T5 to generate a single-phase output voltage U a If the circuit is implemented this way, the efficiency is slightly lower than that of the circuits in Figures 4a and 4b. However, the efficiency can be improved by replacing the diodes with synchronous rectification using (GaN) transistors.

[0059] The variant shown in Figure 4d generates the single-phase output voltage U a with only a single semiconductor switch T3. This represents the most cost-effective variant in terms of the number of transistors, while at the same time offering good efficiency. Even if harmonics of the input current can occur in this circuit variant, their contribution can be limited by the ratio of the secondary voltage to the actual single-phase output voltage U a so that even high power levels up to the kW range can be drawn from the supply network without violating standards.

[0060] In the secondary side shown in Figure 4e, only one of the three phases is shown. The other phases can be designed in the same way. The bipolar semiconductor switches shown there can switch the output pulses in such a way that an alternating voltage can be made available on the output side. Typical mains voltage-optimized transformers can be dispensed with, so that significantly smaller sizes can be realized. Such a circuit makes it possible to exchange active power between different grid levels, e.g. from the low-voltage level (400 V) to the medium-voltage level (~ 1 kV ... 30 kV) with a small design (e.g. due to the reduced requirements for the transformers). Although the invention is shown as non-interleaved in the figures, it is perfectly possible to provide interleaving of the primary side and / or the secondary side without deviating from the invention.

[0061] The invention enables particularly inexpensive but also highly efficient circuits.

[0062] In particular, the invention allows the use of a transistor-effective circuit according to embodiments of the invention for an electrolyzer and / or for a battery charger, but in particular also for an on-board charger.

Claims

Claims 1. Transistor-effective circuit (1) comprising • a primary side (P) for three phases (LI, L2, L3), comprising at least two semiconductor switches (TI, T2), • wherein on the primary side (P) in operation, in addition to a switched-off state (b), a first switched-on state (a) and a second switched-on state (c) are provided, wherein in operation the first switched-on state (a) is followed by a further switched-off state, wherein in operation the second switched-on state (c) is followed by a switched-off state, • a secondary side (S) for a regulated voltage output comprising at least one semiconductor switch (T3...T8), • where switching phases on the secondary side (S) depend on the primary side (P) being switched on, where during operation an input-side alternating voltage (U ) is converted into an adjustable output voltage (U out) is transferred.

2. Transistor-effective circuit according to claim 1, characterized in that the switching frequency of the primary side is more than 9 times a mains frequency applied to the primary side.

3. Transistor-effective circuit according to claim 1 or 2, characterized in that the switching frequency of the secondary side is more than 4 times the switching frequency of the primary side.

4. Transistor-effective circuit according to one of the preceding claims, characterized in that the circuit has fewer than 14 transistors.

5. Transistor-effective circuit according to one of the preceding claims, characterized in that the circuit provides currentless switching on the primary side.

6. Transistor-effective circuit according to one of the preceding claims, characterized in that the transistors comprise silicon carbide transistors or gallium nitride transistors or super junction MOSFET transistors or IGBT transistors.

7. Transistor-effective circuit according to one of the preceding claims, characterized in that the output voltage is a regulated DC voltage.

8. Transistor-effective circuit according to one of the preceding claims, characterized in that the output voltage is a regulated alternating voltage.

9. Use of a transistor-effective circuit according to one of the preceding claims for an electrolyzer.

10. Use of a transistor-effective circuit according to one of the preceding claims for a battery charger, in particular for an on-board charger.

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