DE102014217269A1 - Circuit arrangement for feeding a load and method for its operation - Google Patents

Abstract

In order to provide a star-delta switch for an asynchronous machine without torque, circuitry (100, 200, 300) for feeding a load (110) forming an open multiphase system having a predetermined number of phases is provided to substantially provide a first one DC voltage-configured first energy source (101) or from the first and a substantially provided for supplying a second DC voltage second energy source (201) proposed with the predetermined phase number polyphase voltage, comprising a first converter stage (114) for supplying a matching with the predetermined phase number Number of first terminals (U, V, W) of the load from the first energy source and a second converter stage (115) for supplying a number of second terminals (X, Y, Z) corresponding to the predetermined number of phases of the load from the first or the second energy source , where the first and the second converter stage are adapted to connect the first and second terminals of the load optionally to a star connection or a ring circuit for feeding the load.

Description

The invention relates to a circuit arrangement for feeding a load. The invention further relates to a method for operating such a circuit arrangement.

State of the art

In drive trains modern electric and hybrid vehicles today permanent magnet synchronous machines are preferred due to their high achievable torques and efficiencies and small space requirements compared with asynchronous machines. However, constant and sudden price fluctuations for the production of rare earth raw materials used therein permanent magnets limit a long-term development strategy of mass production of these machines. It is therefore desirable to use the simpler and less expensive asynchronous machines instead of the permanent magnet synchronous machines.

In order to exploit torques that can be achieved with asynchronous machines in all speed ranges, a star-delta changeover is necessary during operation, since an asynchronous machine has a higher torque at lower speeds because of its higher currents in star connection than in delta connection. However, in the star connection the torque requirements for higher speeds are not achieved. In the delta circuit, on the other hand, there is not enough torque in the constant flux range at low speeds.

This operating behavior of the asynchronous machine is in 8th illustrated by an example. Torques M are plotted along the abscissa along the rotational speed D of the asynchronous machine along the ordinate. For a star-connected operation, there is a characteristic of the torque designated by MS, and for operation in delta connection, a curve of the torque denoted by MD is obtained. Suitably takes place in the operation of the asynchronous a star-delta switching at a speed value DU.

From the publication WO 2012/163433 A2 is an asynchronous motor with load-dependent star or delta wiring known. In particular, this document describes a device for the power supply of an asynchronous motor and a method for driving a star contactor and a delta contactor of an asynchronous motor, which are intended to operate asynchronous motors over a large load range with improved efficiency.

For this purpose, it is proposed in the cited document that the device comprises a star contactor and a delta contactor for the asynchronous motor and a logic unit, wherein the logic unit is adapted to control the star contactor and / or delta contactor for the asynchronous motor based on the present motor load of the asynchronous motor. The switching between a star connection at an engine load in the range of 0% -50% of the rated motor load and a delta connection at an engine load in the range of 30% -100% of the rated motor load takes place dynamically and self-recognizing based on the present motor load of the asynchronous motor, in particular by the Detection of the motor current with the aid of the logic module, which activates and / or switches off the star or delta contactor. The asynchronous motor is connected to the delta contactor and the star contactor in such a way that switching the triangular contactor or star contactor results in a modified network topology for the motor windings and thus lowering or increasing the supply voltage to the motor windings of the asynchronous motor. In contrast to conventional star-delta starters with automatic time-dependent switching from the star contactor to the delta contactor, the motor load-dependent control of the triangular contactor and the star contactor is carried out via the logic unit, which analyzes the present motor load of the asynchronous motor as an input variable.

Furthermore, it is stated that the switching operations with the triangular contactor and the star contactor can also be realized by other suitable switching devices, such as soft starters, thyristor switches, relays, etc. It is further stated that the logic unit can be integrated into an existing controller, such as an overload relay, more generally in monitoring devices, e.g. Simocode of the company SIEMENS, or superordinate controls, e.g. PLC, Simocode from SIEMENS, can be integrated.

It turns out, however, that star-delta switchings like those in the document WO 2012/163433 A2 described require a relatively long switching time in one of T. Kume, T. Iwakane, T. Sawa, T. Yoshida and I. Nagai in the paper "A wide constant power range vector controlled AC motor drive using a winding changeover technique", published in IEEE Transactions on Industry Applications, vol. 27, no. 5, pp. 934-939, 1991 100 to 150 milliseconds described example. During this time, the supply current of the engine must be turned off, and you get a corresponding, noticeable torque or power interruption, which prevents use in electric and hybrid vehicles.

DESCRIPTION OF THE INVENTION: Problem, Solution, Advantages

The invention has the object to provide a torque or power interruption-free star-delta switching for an asynchronous machine.

This object is achieved by a circuit arrangement for feeding a load forming an open polyphase system having a predetermined number of phases from a first energy source essentially configured to provide a first DC voltage or from the first and a second energy source essentially configured to provide a second DC voltage the predetermined phase number having multiphase voltage, comprising a first converter stage for supplying a number of first terminals of the load from the first energy source corresponding to the predetermined phase number and a second converter stage for supplying a number of second terminals of the load from the first or the second corresponding to the predetermined phase number Power source, wherein the first and the second converter stage are adapted to supply the load, the first and second terminals of the load optionally to a star connection or a ring switching to connect.

In this case, according to the terms of the general teaching of the multiphase alternating currents, which conform to the definitions of Textbook of Moeller: Guide of Electrical Engineering, Volume I, Fundamentals of Electrical Engineering, 14th Edition 1971, BG Teubner Stuttgart, ISBN 3-519-06400-6, Verl.-Nr. 6400, chapter 11 multiphase alternating currents, pages 420 ff. , are ajar and are used here for both continuous and pulsed AC voltages or currents, referred to as multiphase voltage, a number of AC voltages having mutually evenly distributed over a period intervals phase angles; in the vector diagram, the hands of the alternating voltages are distributed with mutually equal phase angles. Strictly speaking, this is a symmetrical polyphase voltage. The number of alternating voltages is the number of phases.

A load to be fed with such a multiphase voltage has a number of phases or strings which match the number of phases and thus forms a multiphase system. Are these strands of the load not connected to each other, i. isolated from each other, and thus can be fed independently, the load forms an open multi-phase system. Each of the strands has a first terminal and a second terminal. Thus, both the number of first terminals of the load and the number of second terminals of the load coincide with the predetermined number of phases. The order in which the phase positions of the alternating voltages of the polyphase voltage follow one another along a time axis or the vectors of the alternating voltages in the vector diagram is referred to here as phase sequence. Each of the alternating voltages can be fed to a specific one of the strings of the load. Thus, the phase sequence also indicates an order of the strings of the load, in which order the strings are fed. In particular, the first and the second terminals are each to feed themselves in this particular, matching phase sequence. In other words, between each one of the first terminals and one of the same location of the phase sequence associated with the second terminals one strand of the load, which can also be referred to as a current path, arranged.

Under a star connection, the terms from the general teaching of multiphase alternating currents are now referred to as an interconnection of the individual strings of the load, in which all second terminals are combined with a common star point and one of the alternating voltages of the polyphase voltage is supplied to one of the first terminals , On the other hand, a ring circuit is an interconnection of the individual strings of the load, in which the second terminal of each of the strings of the load is connected in each branch point to the first terminal of the string of the load which follows the former string in the phase sequence. In each case one of the alternating voltages of the polyphase voltage is supplied to one of the branch points. In the star connection, therefore, the assigned AC voltage of the polyphase voltage is applied to each string of the load. In the case of the ring circuit, the vectorial difference of the voltage phasors of each of two alternating voltages of the multiphase voltage that follow one another in the phase sequence is applied to each strand of the load.

The converter stages, which are set up to be selectively controlled to form a star connection and a ring circuit, are preferably designed with half bridges each consisting of two electronic switch elements, preferably semiconductor switch elements, particularly preferably transistors or so-called IGBTs. The electronic switching elements of each of the half-bridges are arranged with their main current paths in series, wherein one of the end points of the series circuit is electrically conductively connected to one of two terminals of one of the energy sources. The connection point of the series connection each one of the half bridges, also referred to as a tap of this half-bridge is connected to one of the first or the second terminals of the load. All half bridges, whose Taps are connected to one of the first terminals of the load are combined to the first inverter stage. All half-bridges whose taps are connected to one of the second terminals of the load are combined to form the second converter stage. Thus, the taps and thus the half-bridges within each of the converter stages are also arranged in the phase sequence described or assigned to this phase sequence.

In order to form a star connection, the second converter stage is preferably controllable such that the taps of all half bridges of the second converter stage are conductively connected to one another in a star point. For this purpose, all the electronic switch elements of these half bridges of the second converter stage, which are electrically conductively connected to the same connection of one of the energy sources, or to switch all electronic switch elements of these half bridges of the second converter stage at all. This circuit is to be made in such a way that no current can flow from the energy sources into the half-bridges or the neutral point, for which purpose the energy sources are at least half-sided, i. unipolar, must be separated from this star point.

In order to form a ring circuit, the first and the second converter stage are controlled synchronously such that in each case a half-bridge of the first converter stage is connected to the preceding or following half-bridge in the phase sequence of the second converter stage, i. whose electronic switch elements are switched synchronously. Thus, an interconnection of the individual strings of the load, in which the second terminal of each of the strings of the load is connected in each branch point to the first terminal of that strand of the load following in the phase sequence to the former strand, is given.

Depending on the specification of the phase number of the alternating voltages and thus the strings of the load their interconnection to the ring circuit in three phases as a delta connection, in four phases as a quadrilateral circuit, in six phases as hexagonal circuit, etc., referred to. A particularly preferred case is the three-phase system with three alternating voltages and three strings, as it is widespread as a three-phase system in the electrical power supply. Accordingly, in a preferred embodiment of the circuit arrangement according to the invention, the load is designed as an open three-phase system, and the converter stages each have three half-bridges, one half-bridge for each of the phases.

At this point it should be mentioned that from the document DE 10 2006 003 398 A1 a double ended inverter system for a vehicle for driving an engine or other load of the vehicle is known: The dual ended inverter system includes a first power source and a first power converter system coupled to the first power source and configured to drive the load. The dual ended inverter system further includes a secondary power source, a second capacitor connected in parallel with the secondary power source, and a second power converter system coupled to the secondary power source and configured to drive the load. A controller includes an output coupled to the first inverter system and the second inverter system to provide the first inverter system and the second inverter system with at least one pulse width modulated signal. In this double-ended inverter system, there is an important operating condition in which the primary source of energy provides the load with the full power. In this case, the secondary power source will not deliver power and will not be in a state of charge. One way to do this is simply to close the three upper or the three lower semiconductor switches in the second inverter system to create an artificial star connection in the windings of the motor. While creating an artificial star circuit eliminates any switching losses in the second inverter system, it also restricts the voltage that can be applied to the motor to that which the first inverter system itself could produce. As a result, the motor reaches the limit where field weakening must occur at a lower speed. It is possible to further increase the available motor voltage by generating a voltage through the second inverter system that is 90 degrees out of phase with the current of the motor.

Furthermore, in the document DE 10 2006 003 398 A1 indicates that when the output voltage of the second inverter system is out of phase with that of the phase current by 90 °, the second inverter system does not process active power. However, the voltage generated by the second inverter system contributes to the available voltage of the first inverter system, so that the maximum available voltage of the system has been increased. In essence, the second inverter system provides a portion (less than or equal to 100%) of the reactive power consumed by the load while the first inverter system provides the total active power and remaining reactive power.

However, star-delta switching as in the present invention is not obtained therewith.

The invention enables an increase in the power and the efficiency of the load by using a star-ring switching, in particular a star-delta switching in a three-phase system. In particular, the invention makes it possible to perform this switching power interruption free, since during operation of the circuit arrangement according to the invention no Umschaltzeitintervalle or blanking intervals must be provided, in which the energy supply from the energy sources should be interrupted. This is achieved by using the second converter stage in addition to the first converter stage. The described control of the half bridges of the converter stages, a formation of either a star point for a star connection by at least half-sided Leitend switching all half bridges of the second converter stages or a formation of virtual and / or real Abzweigpunkte for a ring circuit by synchronization of the half bridges is obtained in the manner described without transition , In this case, the formation of a real branch point denotes an electrically conductive interconnection of a first and a second terminal of the load in the manner described; such a real branch point is fed in particular from the first energy source. With the formation of a virtual branch point, the electrically separate but synchronous feeding of this first terminal of the load from the first power source and the second terminal of the load from the second power source is indicated, wherein the designated terminals are supplied at the same time matching voltages, ie AC voltages, so that these connections are always at the same electrical potential.

Advantageous embodiments of the invention are characterized in the subclaims.

According to a preferred embodiment, the circuit arrangement according to the invention is characterized by a training for feeding the load exclusively from the first power source, for which at least one switch element is provided for selectively obtaining the second DC voltage from the first DC voltage of the first power source and for supplying these from the first DC voltage first power source obtained second DC voltage to the second converter stage. The at least one switch element, also referred to as a connection switch, is also advantageously designed as an electronic switch element, preferably with one or more transistors or IGBTs and serves to selectively supply the first DC voltage from the first power source as a second DC voltage to the second converter stage, the circuit arrangement only having the first energy source, a separate second energy source can be omitted. Preferably, the converter stages and the at least one connection switch are combined to form a common power electronics module, for which purpose different integration techniques known per se can be used. As a result, although two converter stages are provided, overall a compact and inexpensive construction is obtained.

In a further preferred embodiment, the circuit arrangement according to the invention is characterized by a design of the first and / or the second energy source with at least one accumulator and / or at least one fuel cell. This embodiment is preferably used in electrically powered vehicles, in particular road vehicles, or in hybrid vehicles. Advantageously, the first and / or the second energy source is formed by a traction battery of such a vehicle. Thus, a very efficient operation of the load with high efficiency in such a vehicle with the energy sources available therein is possible.

According to a further preferred embodiment, the circuit arrangement according to the invention is characterized by a design of the first and / or the second energy source with at least one capacitor, in particular with at least one supercapacitor.

• • aus der statischen Speicherung elektrischer Energie durch Ladungstrennung in Helmholtz-Doppelschichten in einer Doppelschichtkapazität und
• • aus der elektrochemischen Speicherung elektrischer Energie durch faradayschen Ladungstausch mit Hilfe von Redoxreaktionen in einer Pseudokapazität.

As can be seen from the internet encyclopedia "Wikipedia" - cf. the internet appearance " http://de.wikipedia.org/wiki/Superkondensator ", Posted on 06/05/2014 at 11:35 AM - As can be seen, supercapacitors, also called ultracapacitors, are electrochemical capacitors and, as such, a further development of double-layer capacitors, unlike ceramic, foil and electrolytic capacitors, they have no dielectric in the conventional one The capacitance values of these capacitors result from the sum of two high-capacitive storage principles:

• • from the static storage of electrical energy by charge separation in Helmholtz double layers in a double-layer capacitance and
• • from the electrochemical storage of electrical energy by faradaic charge exchange by means of redox reactions in a pseudo-capacitance.

Double-layer and pseudo-capacitance add up to a total capacity in all electrochemical capacitors.

• • Doppelschichtkondensatoren besitzen Kohlenstoffelektroden oder deren Derivate mit einer sehr hohen statischen Doppelschichtkapazität. Der Anteil an faradayscher Pseudokapazität an der Gesamtkapazität ist nur gering.
• • Pseudokondensatoren besitzen Elektroden aus Metalloxiden oder aus leitfähigen Polymeren und haben einen sehr hohen Anteil an faradayscher Pseudokapazität.
• • Hybridkondensatoren besitzen asymmetrische Elektroden, eine mit einer hohen Doppelschicht-, die zweite mit einer hohen Pseudokapazität. Zu den Hybridkondensatoren gehören Lithium-Ionen-Kondensatoren.

Due to the design of their electrodes, supercapacitors are divided into three different capacitor families:

• • Double-layer capacitors have carbon electrodes or their derivatives with a very high static double-layer capacity. The proportion of Faraday pseudo capacity in the total capacity is small.
• • Pseudo-capacitors have electrodes made of metal oxides or of conductive polymers and have a very high proportion of Faraday pseudo-capacitance.
• • Hybrid capacitors have asymmetric electrodes, one with a high bilayer, the second with a high pseudo capacitance. The hybrid capacitors include lithium-ion capacitors.

In supercapacitors, the electrolyte is the conductive connection between two electrodes. This distinguishes them from electrolytic capacitors, in which the electrolyte is the cathode and thus forms the second electrode. Supercapacitors are passive electronic devices that bridge the gap between capacitors and accumulators. Among the capacitors, they have the highest capacitance per component, which is 10,000 times greater than that of electrolytic capacitors at up to 10,000 F / 1.2V. In comparison to accumulators of the same weight, supercapacitors have only about 10% of their energy density, but their power density is about 10 to 100 times greater. Supercapacitors can therefore be charged and discharged much faster. They also withstand much more switching cycles than rechargeable batteries and are therefore suitable as their replacement or supplement when a large switching stress is required.

The field of application of supercapacitors ranges from the provision of smallest streams for data retention from static memories (SRAM) in electronic devices to the field of power electronics, e.g. as a storage of electrical energy in the so-called KERS system of Formula 1 racing cars or in the recovery of braking energy, the so-called recuperation, in vehicles such as buses and trains.

Also from the essay "Supercapacitors - Electrochemical Double Layer Capacitors", published in MTZ - Motortechnische Zeitschrift, Issue 02/2013, pages 158-163, authors: Dr.-Ing. Julia Kowal, Dipl.-Ing. Julia Drillkens, Univ.-Prof. Dr. rer. nat. Dirk Uwe Sauer, published by Springer Automotive Media Wiesbaden GmbH (2013) , It can be seen that as an alternative to batteries for the storage of electrical energy and a capacitor technology is available, which is referred to as electrochemical double-layer capacitors, also called supercaps, ultracaps or supercapacitors. Systematically, electrochemical double-layer capacitors belong to the group of capacitors. They have a structure with porous electrodes and dissolved ions in an organic electrolyte.

Furthermore, it is described in this article that these supercaps store the energy in the electric field between a carbon surface on one side and a Helmholtz layer of ions on the other side. Due to the porous surface structure of the electrodes and the small distance of the Helmholtz layer in the range of a few nanometers, they can save much more energy per volume compared to conventional capacitors. They have a fast response time and the ability to deliver very high currents. This results in a similar performance. At the same time, the supercaps reach two to three orders of magnitude higher cycle lifetimes, since the energy storage essentially proceeds electrostatically and without electrochemical reaction. The electrode materials are therefore not subjected to structural changes in the crystal structure, which makes the electrodes very stable. Because of these characteristics, supercaps have an intermediate position between batteries and capacitors in terms of energy and power. They are thus ideal energy storage devices for all applications where high performance is required for a short time and large numbers of cycles.

Thus, such supercapacitors are advantageously used as energy storage for the circuit arrangement according to the invention. Is e.g. the second energy source is formed with at least one such supercapacitor, energy is preferably supplied to this supercapacitor in a so-called recuperation mode. Such a Rekuperationsmodus is advantageously carried out when braking vehicles, with the kinetic energy of the vehicle electrical energy is recovered. Such recovered energy can be supplied to the supercapacitor and stored therein. In the case of the circuit arrangement according to the invention, electrical and / or mechanical stored in the load, i. potential and / or kinetic energy, which was taken in particular from the first energy source, are passed in recuperation in the supercapacitor. Preferably, such a recuperation mode can also be carried out with specific control of the converter stages, for example by half-side conduction switching and half-side blocking of the half bridges of the first converter stage, whereby this forms a star point separated from the first energy source for the first terminals of the load. The energy is then supplied to the supercapacitor via the second converter stage.

In variations of this embodiment, at least one capacitor and / or at least one supercapacitor may be provided in addition to the first and / or the second energy source disposed parallel thereto, the at least one Capacitor and / or supercapacitor, for example, parallel to at least one fuel cell and / or at least one accumulator of the energy storage to compensate for load fluctuations and / or peaks and / or voltage smoothing and / or suppression serves.

According to a preferred development of the circuit arrangement according to the invention, the first energy source is coupled to the first converter stage via at least one first DC-DC converter and / or the second energy source is coupled to the second converter stage via at least one second DC-DC converter. If only a first energy source is provided, only one DC-DC converter is needed. These DC-DC converters, also designed and designated as so-called "boost / buck converters", are designed to keep constant the voltages to be supplied to the load during the star-ring switching by certain control, since otherwise undesirable oscillations in the transient behavior of the circuit arrangement may occur. In particular, this control is effected by an appropriate change of a modulation index in the voltage conversion.

In a preferred embodiment of the circuit arrangement according to the invention, the load is formed with an electric machine with open windings. Particularly preferably, the load is formed with an asynchronous machine with open windings. Thus, the circuit arrangement according to the invention can advantageously be used for drives. It allows a power or torque interruption-free operation of such an electric machine, in particular a force or torque interruption-free star-ring switching this electric machine. In a particularly preferred embodiment, the load is designed as a three-phase asynchronous machine. Thus, the circuit arrangement according to the invention enables a power or torque interruption-free operation of the three-phase asynchronous machine, in particular a force or torque interruption-free star-delta switching of the three-phase asynchronous machine. Since such an asynchronous machine is constructed very inexpensively and simply without the use of expensive permanent magnets, can be realized with the invention, a very simple and inexpensive constructed drive, which is also and preferably used for electrically powered vehicles and there especially for a traction drive. The invention improves the efficiency and torque of this drive by using an asynchronous machine to the extent that they approach, as much as possible, the respective values of a permanent magnet synchronous machine. Using an asynchronous machine, a comparable performance is achieved with the same installation space as for a permanent magnet synchronous machine. In addition, the circuit arrangement according to the invention can optionally also be used for operating a permanent-magnet-excited synchronous machine instead of the asynchronous machine.

According to a further preferred embodiment, the circuit arrangement according to the invention is characterized by a control stage for controlling the converter stages and / or the at least one switch element and / or the DC-DC converter. By jointly controlling all optionally used in the circuit arrangement according to the invention electronic switch elements, preferably that of the half bridges of the converter stages and additionally the at least one connection switch and optionally also the at least one DC-DC converter, i. "Boost / Buck Converters", by means of a common control stage, a simple and compact construction of the circuit arrangement according to the invention is obtained, with which a synchronization of the type described is achieved simply, precisely and without errors. In particular, the avoidance of synchronization errors between the converter stages is significant.

The above object is further achieved by a method of operating a circuit arrangement of the type described above, wherein for feeding the load from the first or the first and the second energy source, the first and second terminals of the load by controlling at least the inverter stages optionally to a star connection or a ring circuit can be connected. In particular, in a design of the load with an electric machine, preferably an asynchronous machine, the connection to the star connection at low speeds and the connection to the ring circuit at high speeds.

To form the star connection, the electronic switching elements of the half bridges in the second converter stage are switched such that a star point is formed in the second converter stage and at the same time a separation of this star point from the first or the first and the second energy source is effected. When feeding both converter stages from the first energy source provided as the first energy source, in particular the at least one connection switch is switched non-conducting and the half-bridges of the second converter stage at least switched on one side conductive. In the case of separate feeding of the second converter stage from the separate second energy source, the half bridges of the second converter stage are preferably connected in a semi-conducting and half-conducting non-conducting manner, so that over connected to a first terminal of the second power source, the conductive switch elements of the half-bridges of the second inverter stage of the star point is formed and prevented by the connected to a second terminal of the second power source, non-conductive switch elements of the half-bridges of the second converter stage, a current flow from the second energy source.

To form the delta connection, a synchronization of the half bridges of the first and the second converter stage is carried out such that one of the first terminals of the load with the in the phase sequence by a certain number of points in the phase sequence, in particular by one point, adjacent the second terminals the load is fed synchronously, preferably conductively connected, is. As already explained above, as for forming a ring circuit, the first and the second converter stage are synchronously controlled so that in each case a half-bridge of the first converter stage is connected to the preceding or subsequent half-bridge in the phase sequence of the second converter stage, i. whose electronic switch elements are switched synchronously. Thus, an interconnection of the individual strings of the load, in which the second terminal of each of the strings of the load is connected in each branch point to the first terminal of that strand of the load following in the phase sequence to the former strand, is given. Thereby, a connection forming an actual electrical branch point or a match of the voltages applied to these terminals is achieved, which acts as an actual electrical branch point and is also referred to above as a virtual branch point.

The inventive method allows in a simple way the desired, power or torque or torque interruption-free star-ring switching. Preferably, the inventive method for controlling traction drives in electrically operated vehicles can be used.

In an advantageous embodiment of the method according to the invention, the converter stages are controlled pulse width modulated. Thus, the star-ring switching invention is very simple and effective combined with a power control by pulse width modulation, without having to use other circuit components, especially complex and expensive power semiconductors. This development of the method according to the invention thus makes it possible to provide and operate a simply constructed, compact and powerful drive.

Brief description of the drawings

In the drawing, in which matching elements in all figures are given the same reference numerals and to which a repeated description of these elements is omitted, show:

1 a first example of a circuit arrangement according to the invention in block schematic representation,

2 the first example of the circuit arrangement according to the invention 1 in a block diagram in an operating state with a star connection,

3 the first example of the circuit arrangement according to the invention 1 in a block diagram in an operating state with formation of a first branch point of a delta connection,

4 the first example of the circuit arrangement according to the invention 1 in block schematic representation in a further operating state with the formation of a second branch point of a delta connection,

5 Diagrams with switching profiles for the converter stages and the connection switches in star and delta connection and at the changeover time,

6 a second example of a circuit arrangement according to the invention in block schematic representation,

7 a third example of a circuit arrangement according to the invention in block schematic representation, and

8th a diagram showing an example of a curve of a torque M of an asynchronous machine over the speed to illustrate the performance.

The embodiments of the invention shown in the drawing will be described in more detail below.

Preferred embodiment of the invention

In 1 is with the reference numeral 100 a first, reproduced in block schematic representation example of a circuit arrangement according to the invention. The circuit arrangement 100 includes a first energy source 101 , which is arranged to supply substantially a first DC voltage and, for example, with a Accumulator and / or a fuel cell is formed. The first energy source is preferred 101 formed in the present example with a traction battery, also referred to as high-voltage or HV battery, an electrically driven vehicle. A plus pole 102 and a negative pole 103 the first energy source 101 are with a first and a second input terminal 104 respectively. 105 a first DC-DC converter 106 connected via a control input 107 a control signal for controlling a voltage or power which can be output via a positive terminal P and a negative terminal N can be supplied by a suitable change of a modulation index in the voltage conversion. A smoothing capacitor 109 is between the output terminals P, N of the first DC-DC converter 106 arranged. Another smoothing capacitor can be placed between the input terminals 104 . 105 of the first DC-DC converter 106 However, it is encompassed by this and thus in 1 not explicitly shown. Between the positive pole P and the negative pole N of the first DC-DC converter 106 is thus a smoothed DC voltage for feeding a load available.

This load is in 1 designed as an asynchronous machine and with the reference numeral 110 designated. The asynchronous machine 110 forms an open three-phase system with three strands, which are designed here as winding strands, and therefore has the number of phases 3 on. From these strands is a first strand 111 disposed between a first terminal U and a second terminal X; a second strand 112 is disposed between a first terminal V and a second terminal Y, and a third strand 113 is disposed between a first terminal W and a second terminal Z. About the connections U, V, W, X, Y, Z are the strands 111 . 112 . 113 the asynchronous machine 110 fed with a three-phase voltage. This includes the circuit arrangement 110 a first inverter stage 114 through which the first terminals U, V, W of the strands 111 . 112 . 113 the asynchronous machine 110 be fed, and a second inverter stage 115 through which the second terminals X, Y, Z of the strands 111 . 112 . 113 the asynchronous machine 110 be fed.

The first inverter stage 114 has a first, a second and a third half-bridge 116 . 117 respectively. 118 on. This includes the first half bridge 116 a first electronic switch element Q11 and a second electronic switch element Q14, arranged in series connection, the second half-bridge 117 a first electronic switch element Q12 and a second electronic switch element Q15 arranged in series therewith and the third half-bridge 118 a first electronic switch element Q13 and a second electronic switch element Q16 arranged in series therewith. Endpoints of the half-bridges 116 . 117 . 118 , which are formed by their first switching elements Q11, Q12, Q13, are connected to the positive pole P of the first DC-DC converter 106 connected. Opposing endpoints of the half bridges 116 . 117 . 118 , which are formed by the second switching elements Q14, Q15, Q16, are connected to the negative pole N of the first DC-DC converter 106 connected. A connection point of the series connection, ie a tap, between the switching elements Q11, Q14 of the first half-bridge 116 is with the first port U of the first strand 111 the asynchronous machine 110 connected. Similarly, there is a tap between the switching elements Q12, Q15 of the second half-bridge 117 with the first terminal V of the second strand 112 and is a tap between the switching elements Q13, Q16 of the third half-bridge 118 with the first terminal W of the third strand 113 the asynchronous machine 110 connected.

The second converter stage 115 also has a first, a second and a third half-bridge 119 . 120 respectively. 121 on. This includes the first half bridge 119 a first electronic switch element Q21 and a second electronic switch element Q24 arranged in series connection therewith, the second half-bridge 120 a first electronic switch element Q22 and a second electronic switch element Q25 arranged in series therewith and the third half-bridge 121 a first electronic switch element Q23 and a second electronic switch element Q26 arranged in series therewith. Endpoints of the half-bridges 119 . 120 . 121 , which are formed by their first switching elements Q21, Q22, Q23, are in a first node 122 connected with each other. Opposing endpoints of the half bridges 119 . 120 . 121 that are formed by their second switch elements Q24, Q25, Q26 are in a second node 123 connected with each other. A connection point of the series connection, ie a tap, between the switching elements Q21, Q24 of the first half-bridge 119 is to the second terminal X of the first strand 111 the asynchronous machine 110 connected. Similarly, there is a tap between the switch elements Q22, Q25 of the second half-bridge 120 with the second terminal Y of the second strand 112 and is a tap between the switching elements Q23, Q26 of the third half-bridge 121 with the second terminal Z of the third strand 113 the asynchronous machine 110 connected.

In contrast to the first inverter stage 114 are the end points of the half bridges for the second inverter stage 119 . 120 . 121 not directly to the positive pole P or the negative pole N of the first DC-DC converter 106 connected, but to the nodes 122 respectively. 123 , The first node 122 is via a first connection switch V1 to the positive pole P of the first DC-DC converter 106 connected. The second node 123 is via a second connection switch V2 with the negative terminal N of the first DC-DC converter 106 connected. By means of the connection switch V1, V2, the second inverter can thus optionally with the first DC-DC converter 106 connected or disconnected from this. This is the food of the strands 111 . 112 . 113 the asynchronous machine 110 at the second terminals X, Y, Z from the first power source 101 via the second converter stage 115 optionally switched on or off.

The switch elements Q11, Q12, Q13, Q14, Q15, Q16, Q21, Q22, Q23, Q24, Q25 and Q26 of the inverter stages 114 . 115 and the connection switches V1, V2 are formed with bipolar transistors whose collector-emitter paths, ie main current paths, are bridged with free-wheeling diodes.

In 2 is schematically a first operating state of the circuit according to 1 shown in which the strands 111 . 112 . 113 the asynchronous machine 110 through the inverter stages 114 . 115 and the connection switches V1, V2 are operated in a star connection, ie in this first operating state, the first and second terminals U, V, W and X, Y, Z of the asynchronous machine 110 connected to a star connection. This is done by the switching elements Q11, Q12, Q13, Q14, Q15, Q16, Q21, Q22, Q23, Q24, Q25 and Q26 of the inverter stages 114 . 115 and the connection switches V1, V2 assumed switching states are printed by the respective switch elements crosses 124 for symbolizing a non-conducting state and bars printed over the respective switch elements 125 for symbolizing a conductive state indicated. Here are in 2 only the switching states of the switching elements Q21, Q22, Q23, Q24, Q25 and Q26 of the second converter stage 115 and the connection switch V1, V2 explicitly shown, since these are preferably taken statically, so do not change during operation of the asynchronous machine in star connection, whereas the switch elements Q11, Q12, Q13, Q14, Q15 and Q16 of the first inverter stage 114 for feeding the asynchronous machine 110 preferably be controlled pulse width modulated.

In the illustrated first operating state of the star connection, all the switch elements Q21, Q22, Q23, Q24, Q25 and Q26 are the second converter stage 115 permanently, ie continuously for the entire period in which this first operating state persists, switched to the conducting state, so that the second terminals X, Y, Z of the asynchronous machine 110 permanently connected to each other to the star point. The connection switches V1, V2 are permanently in the non-conducting state and thus permanently disconnect the neutral point from the first energy source.

In a modification of this first operating state not shown, the second connection switch V2 may remain in the conducting state and instead the second switching elements Q24, Q25, Q26 of the half bridges 119 . 120 . 121 the second converter stage 115 switched to the non-conducting state, whereas the first switching elements Q21, Q22, Q23 of the half-bridges 119 . 120 . 121 the second converter stage 115 continue to remain in the conductive state and the first connection switch V1 in the non-conductive state. In a modification of the circuit arrangement 100 This modification of the operating state of the star connection can be exploited to the effect that the second connection switch is completely dispensed with and this by an immediate, fixed conductive connection between the second node 123 and the negative terminal N of the first DC-DC converter 106 is replaced. As a result, a switch element can be saved. Since, as shown below, in the operating state of the ring. or delta connection of the second connection switch V2 is operated permanently in the conductive state anyway, have these modifications of the circuit arrangement 100 and the first operating state to the operation in delta connection no influence.

In 3 is schematically a second operating state of the circuit according to 1 shown in which the strands 111 . 112 . 113 the asynchronous machine 110 through the inverter stages 114 . 115 and the connection switches V1, V2 are operated in delta connection, that is, in this first operating state, the first and second terminals U, V, W and X, Y, Z of the asynchronous machine 110 connected to a delta connection.

To form this delta connection, the half-bridges become 116 . 117 . 118 the first inverter stage 114 and the half-bridges 119 . 120 . 121 the second converter stage 115 controlled so synchronously that each one of the first terminals U, V, W of the asynchronous machine 110 with the adjacent in the phase sequence by a point of the second terminals X, Y, Z of the asynchronous machine 110 is conductively connected, ie there will be a half bridge 116 . 117 respectively. 118 the first inverter stage 114 with the preceding or following in the phase sequence half-bridge 119 . 120 respectively. 121 the second converter stage 115 , ie their electronic switch elements Q11, Q12, Q13, Q14, Q15, Q16, Q21, Q22, Q23, Q24, Q25 and Q26, synchronized. This is a connection or interconnection the individual strands 111 . 112 . 113 the asynchronous machine 110 in which the second port X, Y, Z of each of the strands 111 . 112 . 113 the asynchronous machine 110 in each case a branch point with the first port U, V, W of that strand 111 . 112 respectively. 113 the asynchronous machine 110 connected in the phase sequence on the former strand 111 . 112 . 113 follows, given.

• • Die erste Halbbrücke 116 der ersten Umrichterstufe 114 wird mit der dritten Halbbrücke 121 der zweiten Umrichterstufe 115 synchron gesteuert;
• – dazu werden insbesondere das erste Schalterelement Q11 der ersten Halbbrücke 116 der ersten Umrichterstufe 114 und das erste Schalterelement Q23 der dritten Halbbrücke 121 der zweiten Umrichterstufe 115 zueinander synchron geschaltet
• – sowie das zweite Schalterelement Q14 der ersten Halbbrücke 116 der ersten Umrichterstufe 114 und das zweite Schalterelement Q26 der dritten Halbbrücke 121 der zweiten Umrichterstufe 115 zueinander synchron geschaltet.
• • Die zweite Halbbrücke 117 der ersten Umrichterstufe 114 wird mit der ersten Halbbrücke 119 der zweiten Umrichterstufe 115 synchron gesteuert;
• – dazu werden insbesondere das erste Schalterelement Q12 der zweiten Halbbrücke 117 der ersten Umrichterstufe 114 und das erste Schalterelement Q21 der ersten Halbbrücke 119 der zweiten Umrichterstufe 115 zueinander synchron geschaltet
• – sowie das zweite Schalterelement Q15 der zweiten Halbbrücke 117 der ersten Umrichterstufe 114 und das zweite Schalterelement Q24 der ersten Halbbrücke 119 der zweiten Umrichterstufe 115 zueinander synchron geschaltet.
• • Die dritte Halbbrücke 118 der ersten Umrichterstufe 114 wird mit der zweiten Halbbrücke 120 der zweiten Umrichterstufe 115 synchron gesteuert;
• – dazu werden insbesondere das erste Schalterelement Q13 der dritten Halbbrücke 118 der ersten Umrichterstufe 114 und das erste Schalterelement Q22 der zweiten Halbbrücke 120 der zweiten Umrichterstufe 115 zueinander synchron geschaltet
• – sowie das zweite Schalterelement Q16 der dritten Halbbrücke 118 der ersten Umrichterstufe 114 und das zweite Schalterelement Q25 der zweiten Halbbrücke 120 der zweiten Umrichterstufe 115 zueinander synchron geschaltet.

In detail, this means for the formation of a delta connection in the circuit arrangement 100 of the first embodiment according to 1 :

• • The first half bridge 116 the first inverter stage 114 becomes with the third half-bridge 121 the second converter stage 115 synchronously controlled;
• - In particular, the first switch element Q11 of the first half-bridge 116 the first inverter stage 114 and the first switch element Q23 of the third half-bridge 121 the second converter stage 115 synchronized with each other
• - And the second switch element Q14 of the first half-bridge 116 the first inverter stage 114 and the second switch element Q26 of the third half-bridge 121 the second converter stage 115 synchronized with each other.
• • The second half bridge 117 the first inverter stage 114 becomes with the first half bridge 119 the second converter stage 115 synchronously controlled;
• - In particular, the first switch element Q12 of the second half-bridge 117 the first inverter stage 114 and the first switch element Q21 of the first half-bridge 119 the second converter stage 115 synchronized with each other
• - And the second switch element Q15 of the second half-bridge 117 the first inverter stage 114 and the second switch element Q24 of the first half-bridge 119 the second converter stage 115 synchronized with each other.
• • The third half bridge 118 the first inverter stage 114 becomes with the second half bridge 120 the second converter stage 115 synchronously controlled;
• - In particular, the first switch element Q13 of the third half-bridge 118 the first inverter stage 114 and the first switch element Q22 of the second half-bridge 120 the second converter stage 115 synchronized with each other
• - And the second switch element Q16 of the third half-bridge 118 the first inverter stage 114 and the second switch element Q25 of the second half-bridge 120 the second converter stage 115 synchronized with each other.

The two connection switches V1 and V2 remain permanently conductive for the formation of the delta connection.

In 3 is symbolized by way of example a switching state in which in the context of synchronous control of the first half-bridge 116 the first inverter stage 114 with the third half bridge 121 the second converter stage 115 the first switch element Q11 of the first half-bridge 116 the first inverter stage 114 and the first switch element Q23 of the third half-bridge 121 the second converter stage 115 conductive and the second switch element Q14 of the first half-bridge 116 the first inverter stage 114 and the second switch element Q26 of the third half-bridge 121 the second converter stage 115 are switched non-conductive. The conductive first connection switch V1 then provides a conductive connection between the first connection U of the first strand 111 and the second terminal Z of the third strand 113 the asynchronous machine 110 , in the 3 highlighted and with the reference numeral 126 is designated. The connection 126 represents a branch point of the delta connection, here with the positive pole P of the first DC-DC converter 106 connected is.

In 4 is in modification of the in 3 shown switching state as a third operating state of the circuit according to 1 exemplifies a switching state, in which in the context of the synchronous control of the first half-bridge 116 the first inverter stage 114 with the third half bridge 121 the second converter stage 115 now the first switch element Q11 of the first half-bridge 116 the first inverter stage 114 and the first switch element Q23 of the third half-bridge 121 the second converter stage 115 nonconductive and the second switch element Q14 of the first half-bridge 116 the first inverter stage 114 and the second switch element Q26 of the third half-bridge 121 the second converter stage 115 are switched on. Due to the conductively connected second connection switch V2, there continues to be a conductive connection between the first connection U of the first strand 111 and the second terminal Z of the third strand 113 the asynchronous machine 110 , in the 4 highlighted and with the reference numeral 127 is designated. The connection 127 sets the same branch point of the delta connection as in 3 group; However, this branch point is now with the negative terminal N of the first DC-DC converter 106 connected.

For controlling the inverter stages 114 . 115 and the connection switch V1, V2 in the above-described manner includes the circuit arrangement 100 to 1 a tax step 128 , This is via control lines 129 with the converter stages 114 . 115 and the connection switches V1, V2 connected. Via another control line 130 will also be the first DC-DC converter 106 at its control input 107 controlled.

5 shows exemplary diagrams with switching curves for the switching elements Q11 to Q16 and Q21 to Q26 of the inverter stages 114 . 115 and the connection switches V1, V2 in star and delta connection and in the switching time tu between star and delta connection, plotted as a signal value along the ordinate over time t along the abscissa. In this case, with a signal value "0" of the switching waveforms a non-switched state and with a signal value "1" a conductive state of the respective switch element Q11 to Q16 and Q21 to Q26 or the respective connection switch V1, V2 respectively. To the left of the switching time tu, ie for times t less than tu, are in the diagram after 5 Switching curves for star operation reproduced. Right of the switching time tu, ie for times t greater than tu, switching characteristics for the triangular operation are reproduced. With t1 a first time is designated at which the circuit arrangement after 1 the in 2 shown and described to first operating state or switching state occupies. With t2 is designated a second time at which the circuit arrangement after 1 the in 3 illustrated and described second operating state or switching state occupies, and with t3 is a third time designated at which the circuit arrangement according to 1 the in 4 illustrated and described to third operating state or switching state occupies. At the switching time tu, the switching from star connection to delta connection takes place. In the 5 shown switching waveforms form a kind of "undershoot", also referred to as "carrier-based pulse width modulation".

Out 5 is clearly seen that in the circuit arrangement according to the invention between star operation and triangular operation no switching time, ie no business interruption, occurs, but rather pass these two modes when switching directly into each other. Thus, a torque or power interruption-free switching between star and delta operation is achieved.

6 shows a second example of a circuit arrangement according to the invention in block-schematic representation, designated by the reference numeral 200 , In a modification of the circuit arrangement 100 to 1 are the connection switch V1, V2 omitted in this example. Instead, the circuitry includes 200 a second energy source 201 from the still existing first source of energy 101 is arranged independently and electrically separated. The second energy source is preferably designed as an accumulator, eg traction battery, or fuel cell. In the circuit arrangement 200 are the first terminals U, V, W of the strands of the load, which in turn here by an asynchronous machine 110 is formed, again from the first source of energy 101 over the first DC-DC converter 106 and the first inverter stage 114 fed in 6 for the sake of simplicity in a common circuit block 202 are shown. In a practical construction, the components of the first DC-DC converter 106 and the first inverter stage 114 also be summarized in a common power electronics module. In a corresponding manner, a second DC-DC converter is provided, via which the second terminals X, Y, Z of the strings of the load, ie the asynchronous machine 110 , now from the second energy source 201 via the second converter stage 115 be fed. In the presentation of the 6 These are the second DC-DC converter and the second converter stage 115 simplified in another common circuit block 203 summarized. In a practical construction, the components of the second DC-DC converter and the second converter stage 115 be summarized again in a common power electronics module, and particularly preferably form the components of the first DC-DC converter 106 , the first inverter stage 114 , the second DC-DC converter and the second converter stage 115 all together a single common power electronics module. A smoothing capacitor 204 is parallel to the second energy source 201 arranged.

7 shows in a further advantageous modification of the circuit arrangement 200 to 6 a third example of a circuit arrangement according to the invention in block schematic representation, designated by the reference numeral 300 , In the circuit arrangement 300 is the second energy source with a capacitor, preferably a so-called supercapacitor 301 , educated. This is via the second converter stage 115 to the second terminals X, Y, Z of the strings of the asynchronous machine 110 connected. The supercapacitor is preferred 301 in a Rekuperationsmodus, ie at a made with the help of the asynchronous braking process of a vehicle chosen here by way of example, in which the circuit arrangement 300 is used, supplied by the asynchronous machine from the kinetic energy of the vehicle recovered electrical energy and stored therein. Advantageous for this purpose, the converter stages 114 . 115 and the first DC-DC converter 106 or the circuit block 202 controlled accordingly; For example, by half-side non-conductive switching of the half-bridges 116 . 117 . 118 first inverter stage 114 the first energy source 101 from the asynchronous machine 110 disconnected and by conducting the other halves of the half-bridges 116 . 117 . 118 first inverter stage 114 the asynchronous machine 110 when Generator operated in star connection, via the second converter stage 115 the supercapacitor 301 invites.

The circuit arrangements 200 and 300 after the 6 and 7 also have a tax level 128 on, which is not shown for the sake of simplicity. On the other hand, it is already played 1 mentioned another smoothing capacitor between the input terminals 104 . 105 of the first DC-DC converter 106 , the input terminals of the common circuit block 202 form. This smoothing capacitor is denoted by the reference numeral 108 and parallel to the first energy source 101 arranged.

LIST OF REFERENCE NUMBERS

100

Circuit arrangement, first example

101

First energy source of 100 (Traction battery)

102

Positive pole of 101

103

Negative pole of 101

104

First input terminal of 106

105

Second input connection of 106

106

First DC-DC converter

107

Control input from 106

108

Another smoothing capacitor between 104 and 105 or parallel to 101

109

Smoothing capacitor between P and N.

110

Asynchronous machine: load

111

First strand of 110

112

Second strand of 110

113

Third strand of 110

114

First inverter stage

115

Second converter stage

116

First half bridge of 114

117

Second half bridge of 114

118

Third half bridge of 114

119

First half bridge of 115

120

Second half bridge of 115

121

Third half bridge of 115

122

First node of 115

123

Second node of 115

124

Cross symbolizing non-conducting state of Q11-Q26, V1, V2

125

Bar symbolizing the conductive state of Q11-Q26, V1, V2

126

Branch point, connection of U and Z with P

127

Branch point, connection of U and Z to N

128

control stage

129

Control cables from 128 at 114 . 115 , V1, V2

130

Further control line from 128 at 107

200

Circuitry, second example

201

Second energy source

202

Circuit block; e.g. Power electronics module

203

Another circuit block; e.g. Power electronics module

204

smoothing capacitor

300

Circuitry, third example

301

Capacitor; prefers supercapacitor

D

Speed of the asynchronous machine

YOU

Speed value of the asynchronous machine with star-delta changeover

M

Torque of the asynchronous machine

MD

Course of M during operation of the asynchronous machine in delta connection

MS

Course of M during operation of the asynchronous machine in star connection

N

Negative pole of 106

P

Positive pole of 106

Q11

First switch element of 116 in 114

Q12

First switch element of 117 in 114

Q13

First switch element of 118 in 114

Q14

Second switch element of 116 in 114

Q15

Second switch element of 117 in 114

Q16

Second switch element of 118 in 114

Q21

First switch element of 119 in 115

Q22

First switch element of 120 in 115

Q23

First switch element of 121 in 115

Q24

Second switch element of 119 in 115

Q25

Second switch element of 120 in 115

Q26

Second switch element of 121 in 115

t

Time

t1

First time: first operating state

t2

Second time: second operating state

t3

Third time: third operating state

tu

switchover

V1

First connection switch

V2

Second connection switch

U

First connection of 111

V

First connection of 112

W

First connection of 113

X

Second connection of 111

Y

Second connection of 112

Z

Second connection of 113

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2012/163433 A2 [0005, 0008]
• DE 102006003398 A1 [0018, 0019]

Cited non-patent literature

• T. Kume, T. Iwakane, T. Sawa, T. Yoshida and I. Nagai in the paper "A wide constant power range vector controlled AC motor drive using a winding changeover technique", published in IEEE Transactions on Industry Applications, vol. 27, no. 5, pp. 934-939, 1991 [0008]
• Textbook of Moeller: Guide of Electrical Engineering, Volume I, Fundamentals of Electrical Engineering, 14th Edition 1971, BG Teubner Stuttgart, ISBN 3-519-06400-6, Verl.-Nr. 6400, chapter 11 multiphase alternating currents, pages 420 ff. [0011]
• http://en.wikipedia.org/wiki/Superkondensator [0026]
• "Supercapacitors - Electrochemical Double Layer Capacitors", published in MTZ - Motortechnische Zeitschrift, Issue 02/2013, pages 158-163, authors: Dr.-Ing. Julia Kowal, Dipl.-Ing. Julia Drillkens, Univ.-Prof. Dr. rer. nat. Dirk Uwe Sauer, published by Springer Automotive Media Wiesbaden GmbH (2013) [0031]

Claims (10)

Circuit arrangement ( 100 ; 200 ; 300 ) for feeding a load forming an open multiphase system having a predetermined number of phases ( 110 ) of a first energy source, essentially configured to provide a first DC voltage ( 101 ) or from the first ( 101 ) and a second energy source substantially configured to provide a second DC voltage ( 201 ) having a predetermined phase number having multi-phase voltage, comprising a first converter stage ( 114 ) for feeding a number of first terminals (U, V, W) of the load which coincide with the predetermined number of phases ( 110 ) from the first energy source ( 101 ) and a second converter stage ( 115 ) for feeding a number of second terminals (X, Y, Z) of the load which coincide with the predetermined number of phases ( 110 ) from the first ( 101 ) or the second energy source ( 201 ), the first ( 114 ) and the second converter stage ( 115 ) are adapted to feed the load ( 110 ) the first (U, V, W) and second (X, Y, Z) connections of the load ( 110 ) optionally to connect to a star connection or a ring circuit. Circuit arrangement ( 100 ) according to claim 1, characterized by a training for feeding the load ( 110 ) exclusively from the first energy source ( 101 ), for which at least one switch element (V1, V2) is provided for optionally obtaining the second DC voltage from the first DC voltage of the first energy source ( 101 ) and for supplying them from the first DC voltage of the first energy source ( 101 ) obtained second DC voltage to the second converter stage ( 115 ). Circuit arrangement ( 100 ; 200 ) according to claim 1 or 2, characterized by a design of the first ( 101 ) and / or the second energy source ( 201 ) with at least one accumulator and / or at least one fuel cell. Circuit arrangement ( 300 ) according to claim 1, 2 or 3, characterized by a design of the first ( 101 ) and / or the second energy source ( 201 ) with at least one capacitor, in particular with at least one supercapacitor ( 301 ). Circuit arrangement ( 100 ; 200 ; 300 ) according to at least one of the preceding claims, characterized in that the first energy source ( 101 ) via at least one first DC-DC converter ( 106 ) with the first converter stage ( 114 ) and / or that the second energy source ( 201 ) via at least one second DC-DC converter with the second converter stage ( 115 ) is coupled. Circuit arrangement ( 100 ; 200 ; 300 ) according to at least one of the preceding claims, characterized in that the load ( 110 ) is formed with an electric machine with open windings. Circuit arrangement ( 100 ; 200 ; 300 ) according to claim 6, characterized in that the load ( 110 ) is formed with an asynchronous machine with open windings. Circuit arrangement ( 100 ; 200 ; 300 ) according to at least one of the preceding claims, characterized by a control stage ( 128 ) for controlling the converter stages ( 114 . 115 ) and / or the at least one switch element (V1, V2) and / or the DC-DC converter ( 106 ). Method for operating a circuit arrangement (according to at least one of the preceding claims) ( 100 ; 200 ; 300 ), characterized in that for feeding the load ( 110 ) from the first ( 101 ) or the first ( 101 ) and the second energy source ( 201 ) the first (U, V, W) and second (X, Y, Z) connections of the load ( 110 ) by controlling at least the converter stages ( 114 ; 115 ) are selectively connected to a star connection or a ring circuit. Method according to Claim 9, characterized in that the converter stages ( 114 ; 115 ) are controlled pulse width modulated.

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