Method, circuit arrangement and energy supply system for generating polyphase alternating current

Abstract

The invention relates to a method for generating polyphase alternating current, in particular three-phase alternating current, by interconnecting a plurality of DC voltage sources (3), the method having at least the following method steps: - providing a configurable DC voltage string (5) for each phase (L1, L2, L3) of the polyphase alternating current, wherein each configurable DC voltage string (5) is formed by a plurality of DC voltage sources (3), which can be interconnected in a configurable series circuit; - arranging the configurable DC voltage strings (5) in a polygon circuit, in particular a triangular circuit; - providing a neutral earthing transformer (10) for realizing a common neutral point (N) of all configurable DC voltage strings (5); and - configuring the configurable DC voltage strings (5) such that polyphase alternating current is provided and a zero-phase-sequence system current is also formed for charge balancing between the configurable DC voltage strings (5).

Description

Field of the Invention

[0001] The present invention relates to a method for generating polyphase alternating current, in particular three-phase alternating current, by interconnecting a plurality of DC voltage sources. The present invention also relates to a computer program for performing the method.

[0002] The present invention also relates to a circuit arrangement for generating polyphase alternating current, in particular three-phase alternating current, from a plurality of DC voltage sources, the circuit arrangement comprising configurable DC voltage strings for each phase of the polyphase alternating current, wherein each configurable DC voltage string is configured to interconnect a plurality of DC voltage sources in a configurable series circuit, and these voltage sources can be connected to the configurable DC voltage string.

[0003] The present invention also relates to an energy supply system having a circuit arrangement for generating polyphase alternating current and a plurality of DC voltage sources. Background Art

[0004] Battery storage systems are sometimes used in energy supply systems, such as photovoltaic home storage devices ("solar batteries") for storing surplus production from photovoltaic systems or power batteries ("high-voltage storage devices") for powering the electric motors or drive units of electric vehicles. Such battery storage systems sometimes require battery voltages of several hundred volts. However, since the cell voltage of a single battery cell is only a few volts (for example, the voltage of a lithium-ion battery is 3.7 V), many single battery cells need to be connected in series to form a battery pack or rechargeable battery pack (hereinafter also simply referred to as a "battery").

[0005] Due to manufacturing reasons, each battery cell of a battery has different characteristics, such as battery capacity, self-discharge rate, and temperature characteristics. Over time, these differences are further exacerbated by aging effects. Therefore, some battery cells have not reached their maximum charge level during the charging process, while other battery cells are already fully charged. Overcharging the already fully charged battery will ultimately lead to battery damage or even destruction. To prevent this, the charging process must be aborted prematurely.

[0006] The discharging process is similar to the charging process. For example, while some battery cells have been fully discharged, other battery cells sometimes still store enough energy to continue driving an electric vehicle. In the example of an electric vehicle, the driving operation will ultimately have to abort the discharging process prematurely, otherwise the weaker battery cells will be deeply discharged, which, like overcharging, may cause battery damage.

[0007] To ensure a smooth charging and discharging process, a battery management system ("BMS") is used to equalize the charge among individual battery cells. See J. Qi, D. Lu., "Review of Battery Cell Balancing Techniques", Australasian Universities Power Engineering Conference, AUPEC 2014, Curtin University, Perth, Australia, 28 Sept.-1 Oct. 2014.

[0008] The most commonly used method in the prior art is the so-called passive charge equalization. In this case, the fully charged battery cells are discharged again through resistors, while the other battery cells are further charged. An obvious disadvantage of this method is that valuable electrical energy is lost in this case, and this method also does not provide a solution for the discharging process.

[0009] With the help of active charge equalization, the passive charge equalization problem can be solved. However, this technology requires complex circuits with power electronic components and complex open-loop control. For example, each battery cell in an inductive equalization circuit may require two metal-oxide-semiconductor field-effect transistors (MOSFETs); usually even four in a capacitive equalization circuit. Inductors, transformers or capacitors are also required as energy storage devices.

[0010] Self-commutated inverters are usually used to generate three-phase voltages, for example, for motors or electric motors in electric vehicles. Usually, such an inverter consists of six power electronic valves, which are interconnected to form a three-phase bridge. In this "two-point inverter", a sinusoidal alternating voltage is generated by a pulsed voltage with three voltage levels (0, ±U DC ). The level of the voltage pulse depends on the battery voltage U DC , so the level of the voltage pulse is constant. To generate an alternating voltage, the duration of the voltage pulse can vary with the actuator. Usually, the pulse-width modulation (PWM) method is used for calculation. However, in this case, high interference voltages will appear in the alternating voltage of the superimposed frequency. To reduce voltage harmonics, it is known to increase the clock frequency of the inverter. Therefore, the clock frequency of modern converters is usually in the range of several kHz to 100 kHz. However, the switching losses of the inverter increase proportionally with its clock frequency.

[0011] To avoid these problems, as suggested, for example, in DE 10 2011 004 248 A1, modular inverters can be used. Using this technology, individual battery cells are not directly connected in series, but rather via a power electronic H-bridge circuit to increase the number of voltage levels. In this way, for a specified voltage quality, the clock frequency can be reduced, thereby reducing the switching losses of the inverter. Thus, the single-phase sinusoidal output voltage is not generated here by a pulsed voltage, but rather by a voltage with a stepped pattern having small steps. In such a "multi-level inverter", the level of the lowest voltage level typically corresponds to the battery voltage of the battery used (e.g., 3.7 V).

[0012] Since individual battery cells can be connected via separate H-bridges, charge equalization of the battery cells is possible. If an individual battery cell fails, the inverter with the "healthy" battery cells can continue to operate safely. The defective battery cell can be switched off and bypassed, and thus the defective battery can be replaced safely. Therefore, the availability is significantly higher than that of a direct series connection of battery cells.

[0013] The described circuit essentially represents a combination of a multi-level inverter, active charge equalization, and distributed battery management. In the case of a circuit fault, only one battery cell can be short-circuited, which is also advantageous for safety. The residual current and the released energy are significantly lower than those of a conventional series connection. In addition, after the inverter is switched off, only the voltage of a single battery exists. This makes maintenance work easier. Battery cells of different ages and types can be used in the battery block. This makes it possible to replace defective battery cells and thus significantly increases the service life of the battery block.

[0014] The described principle may be applicable to single-phase loads and even to three-phase loads. For example, as described in DE 102011086 545A1, a three-phase modular inverter can be implemented by three modularly configurable DC voltage strings or multi-level inverters interconnected in a star circuit.

[0015] However, the main advantage of the active charge equalization of modular inverter technology can only be applied to a limited extent in this circuit. Because direct charge equalization between battery cells in different phases is not possible. The charge equalization between phases is only affected by the different active powers of the three phases. The resulting excess or deficit electrical energy in each phase must be compensated by the supply network. However, the standards in many countries do not allow such charge equalization based on the supply network, and in the case of island operation, i.e., when there is no supply network at all, such charge equalization is simply impossible. Summary of the Invention

[0016] In view of the known prior art, the object of the present invention is to provide a method for generating polyphase alternating current, in particular three-phase alternating current, by interconnecting a plurality of DC voltage sources, which method improves the charge balance between the DC voltage sources.

[0017] The present invention is also based on the object of providing an advantageous computer program for performing such a method.

[0018] Furthermore, the object of the present invention is to provide a circuit arrangement for generating polyphase alternating current, in particular three-phase alternating current, from a plurality of DC voltage sources while improving the charge balance between the DC voltage sources.

[0019] Another object of the present invention is to provide a polyphase energy supply system based on a plurality of DC voltage sources, which has an improved charge balance between the DC voltage sources.

[0020] The present invention provides a method for generating polyphase alternating current by interconnecting a plurality of DC voltage sources.

[0021] The polyphase alternating current to be generated may preferably be three-phase alternating current or "three-phase current". However, in principle, any number of phases may be provided, for example, only two phases or more than three phases, such as four phases or five phases. The present invention will be mainly described below by means of three-phase alternating current, however, this should be understood as being merely an example and not a limitation.

[0022] The phases of the polyphase alternating current may be set together or individually in terms of amplitude, phase and / or frequency.

[0023] The DC voltage source may in particular be a single cell of a battery or a group of a plurality of interconnected cells of a battery ("battery module"). However, the DC voltage source may also be a complete battery or a group of a plurality of batteries.

[0024] In this case, "battery" may be understood to refer both to a rechargeable storage device (i.e., "rechargeable battery" / "rechargeable battery pack"), the individual cells of which are also referred to as "energy storage cells", and to a non-rechargeable storage device. A battery or battery pack may also have only one cell. Therefore, the present invention should not be understood as being limited to a battery having a plurality of interconnected cells. Furthermore, in the context of the present specification, a battery may also be used to denote a device for storing electrical energy, the electrical energy of which is not or not only generated electrochemically (e.g., a capacitor).

[0025] However, basically, the DC voltage source can be any DC voltage source, that is to say, for example, it can also be a DC voltage provided by electronic components, such as a DC voltage provided by a rectifier and / or a DC-DC converter on the output side. In particular, the DC voltage source can also be a DC voltage energy source, such as a solar cell or a photovoltaic cell. For the sake of simplicity, the DC voltage source is sometimes referred to as a battery cell of a common battery in the following and above texts. However, this should not be construed as a limitation, but only as an example.

[0026] In the context of this method, the present invention provides configurable DC voltage strings for each phase of a polyphase alternating current. Each configurable DC voltage string is formed by a plurality of DC voltage sources, which can be interconnected in a configurable series circuit. The configurable DC voltage string is configured (for example, by a common open-loop control device or by corresponding open-loop control devices) to provide the desired polyphase alternating current.

[0027] The present invention provides configurable DC voltage strings arranged in a polygon circuit. In the case of providing three-phase alternating current, this can especially be a triangular circuit.

[0028] Therefore, the polyphase alternating current can be provided by a plurality of individual configurable DC voltage strings corresponding to the number of phases provided, and each of these DC voltage strings individually generates only single-phase alternating current.

[0029] Compared with the traditional star circuit in a modular inverter, the proposed polygon circuit allows the formation of balanced currents in three phases for charge balancing between phases. This balanced current is hereinafter referred to as the "zero-phase sequence system current". The polygon circuit (for example, a triangular circuit in the case of three-phase alternating current) can ensure that the circuit does not supply zero-phase sequence system current to the outside, that is, does not supply zero-phase sequence system current in the expected load current. Therefore, the balanced current or zero-phase sequence system current is not obvious in the user network. Therefore, charge balancing between individual phases, that is, charge balancing between individual configurable DC voltage strings in the current case, can be achieved without affecting the external supply network, even in a pure island network.

[0030] Therefore, the present invention provides configurable DC voltage strings to be configured (for example, by a common open-loop control device or corresponding open-loop control devices) such that a zero-phase sequence system current for charge balancing between configurable DC voltage strings is formed.

[0031] This means that charge balancing can be performed with maximum flexibility between all relevant DC voltage sources, regardless of the phase in which the DC voltage source is located or the DC voltage string.

[0032] The present invention also provides a neutral-grounded transformer, the purpose of which is to achieve a common neutral point for all configurable DC voltage strings.

[0033] Since the polygonal circuit (e.g., triangular circuit) proposed above has no neutral point, it cannot be loaded in a single phase. Therefore, it is recommended to provide a separate neutral grounding transformer.

[0034] Therefore, modular inverter technology with all the main advantages can be used, and this technology can provide comprehensive and direct charge balancing between phases and combine the possibility of single-phase loads of the provided power supply system.

[0035] For charge balancing between DC voltage sources (especially also between DC voltage sources in the same phase), the charge difference of the DC voltage sources can be detected, and the detected charge difference is considered when interconnecting the DC voltage sources to perform charge balancing.

[0036] Preferably, charge balancing (especially charge balancing of DC voltage sources within the same phase) can be achieved by affecting the load duration of the corresponding DC voltage sources when generating the AC voltage. This means that the DC voltage source with a higher remaining charge bears the load for a longer time than the DC voltage source with a lower remaining charge. Therefore, the current conduction duration of the DC voltage source is preferably used as an open-loop control parameter for charge balancing. For example, this method can be called "Rotating Balancing". However, in principle, within the scope of the present invention (especially in charge balancing between phases), passive charge balancing or active charge balancing can also be provided.

[0037] To detect the charge difference, a corresponding sensor unit can be used, which detects the voltage and / or current of, for example, individual DC voltage sources, groups of DC voltage sources, and / or common DC voltage strings or DC voltage sources of a common phase.

[0038] Preferably, the interconnection of the DC voltage sources for generating the AC voltage is defined or modified according to charge balancing.

[0039] For example, charge balancing between phases can be achieved by the phase with the least charge receiving charge from the other (two) phases or by the phase with the most charge providing charge to the other (two) phases.

[0040] In an advantageous configuration of the present invention, it can be stipulated that the AC voltage or polyphase alternating current is preferably generated in an approximately stepped shape.

[0041] The AC voltage in each phase can be generated by summing the voltages of the respective DC voltage sources of a common DC voltage string, the respective voltages being in a stepped pattern with small steps. The level of the lowest voltage level can correspond to the output voltage of the respective DC voltage source (e.g., the cell voltage of a battery cell, e.g., 3.7 V). In this way, the high clock frequencies normally required for the pulse-width modulated output voltage and the associated switching losses can be greatly reduced.

[0042] The described principle is particularly advantageously applicable in the context of configurable series circuits, since the series circuit can be conveniently and flexibly adapted to charge equalization. However, this does not exclude, for example, the fact that in the context of the present invention, the DC voltage sources can also optionally be interconnected with fixed wiring, for example in series and / or parallel circuits. For example, a battery module can be formed by two, three, four, five, six, seven, eight, nine, ten or even more permanently interconnected battery cells, which can then be interconnected with other battery modules or battery cells in a configurable manner. The fixed wiring of the DC voltage sources or battery pack cells can be achieved by, for example, a bus bar or other suitable electrical conductor.

[0043] In an advantageous refinement of the invention, a symmetric three-phase alternating current can be provided by appropriately configuring the interconnection of the respective DC voltage sources of the respective configurable DC voltage strings, with the following relationship preferably existing between the AC voltages of the respective phases: and where the peak value is and the network frequency is f.

[0044] If required, a person skilled in the art can also easily establish similar relationships for polyphase alternating currents with only two phases or more than three phases.

[0045] For example, for a 400 V three-phase network, the peak value of the AC voltage can be 566 V and the network frequency is 50 Hz (e.g., for applications in Germany).

[0046] According to an improvement of the invention, it can be stipulated that the zero-sequence system currents in each configurable DC voltage string are the same in magnitude and phase.

[0047] In particular, it can be stipulated that the zero-sequence system currents are formed by appropriately configuring the interconnection of the respective DC voltage sources of the respective configurable DC voltage strings, and the zero-sequence system voltages according to are added to the AC voltages of the respective phases, where the magnitude of the zero-sequence system voltage and the phase angle

[0048] Therefore, considering the zero-sequence system current, the following definitions may apply to a single AC voltage:

[0049]

[0050] and

[0051]

[0052] Optionally, considering the relationship of the zero-sequence system voltage as

[0053]

[0054] where, is the d-component, is the q-component, and each AC voltage can also be determined as:

[0055]

[0056] and

[0057]

[0058] The d-component and the q-component have a phase shift of 90° with respect to each other and are orthogonal (perpendicular) to each other as phasors. The d-component can be in phase with one of the hybrid system voltages (e.g., in phase with u L1 (t), i.e., in phase with phase L1).

[0059] An additional voltage component or the zero-sequence system voltage u0(t) can be used to generate a zero-sequence system current I0 with a specific RMS value I0 and phase angle I0 = I d0 + I q0 where I 0 can be decomposed into the d-component I d0 and the q-component I q0 . Similar to the voltage, the two current components I d0 and I q0 are also orthogonal as phasors and have a phase shift of 90° with respect to each other. In this example, the d-component is in phase with the positive-sequence system voltage u of phase L1 L1 (t). Therefore, the following relationships apply:

[0060]

[0061] and

[0062]

[0063] where I is the magnitude of the positive phase sequence system current of each phase, and is the phase angle.

[0064] In an improvement of the present invention, one or more closed-loop control methods can be provided for determining the zero-phase sequence system current.

[0065] The zero-phase sequence system voltage can be used as the manipulated variable of the closed-loop control, the target value of the zero-phase sequence system current can be used as the reference variable, and the captured actual value of the zero-phase sequence system current can be used as the closed-loop control variable.

[0066] In an improvement of the present invention, it can be set that the q-component of the zero-phase sequence system current is minimized. Preferably, the target value of the q-component is zero, or the q-component is controlled to zero in a closed-loop manner.

[0067] This makes it possible to minimize the losses caused by charge balancing. Preferably, no reactive power (reactive power = zero) is provided in the zero-phase sequence system.

[0068] In an advantageous improvement of the present invention, it can be stipulated that the target value of the d-component of the zero-phase sequence system current is determined in consideration of the charge difference between the DC voltage sources of the DC voltage string.

[0069] Preferably, the target value of the d-component of the zero-phase sequence system current is determined according to its proportional relationship with the charge difference between the DC voltage sources of the DC voltage string.

[0070] The d-component of the zero-phase sequence system current can advantageously be controlled in a closed-loop manner to a value determined according to the level of the charge difference, for example, 1 A for a 1% charge difference.

[0071] At this point, it should be emphasized that the above method steps do not have to be executed in the order first described or mentioned in the specification or claims. For example, if not excluded technically, individual method steps or groups of method steps can thus be interchanged. The method steps can also be combined with each other, divided into separate intermediate steps or supplemented with intermediate steps. The method is not necessarily described decisively by the listed method steps and can be supplemented with other method steps not mentioned either.

[0072] The present invention also relates to a computer program including control instructions, which, when executed by an open-loop control device, cause the open-loop control device to execute the methods according to the above and following embodiments.

[0073] The open-loop control device can be designed as a microprocessor. Instead of a microprocessor, any other device for implementing the open-loop control device can also be provided, such as a device of one or more discrete electronic components on a printed circuit board, a programmable logic controller (PLC), an application-specific integrated circuit (ASIC), or another programmable circuit, such as a field-programmable gate array (FPGA), a programmable logic device (PLA), and / or a commercial computer. The open-loop control device can also be produced by a combination of multiple electronic components, which are distributed and arranged dispersedly within the circuit device, and will also be mentioned hereinafter.

[0074] The open-loop control device can also be a functional module of a higher-level open-loop control unit, such as a functional module of a battery management system of a DC voltage source or an open-loop control unit of an energy supply system (such as a vehicle) also mentioned below.

[0075] The present invention also relates to a circuit device for generating polyphase alternating current, in particular three-phase alternating current, from multiple DC voltage sources. The circuit device has configurable DC voltage strings for each phase of the polyphase alternating current, where each configurable DC voltage string is configured to interconnect multiple DC voltage sources in a configurable series circuit, multiple voltage sources can be connected to the configurable DC voltage strings, and where the configurable DC voltage strings are arranged in a polygon circuit, in particular a triangular circuit. The circuit device also has a neutral earthing transformer for realizing a common neutral point of all configurable DC voltage strings, and has an open-loop control device, which is configured to configure the configurable DC voltage strings such that polyphase alternating current is provided and a zero-phase-sequence system current is also formed for charge balancing between the configurable DC voltage strings.

[0076] Preferably, at least one DC voltage source should not be understood as a component of the circuit device.

[0077] The proposed new circuit device is very particularly suitable for a three-phase modular inverter with a battery as an energy storage device. The specific advantage of the proposed circuit device is the possibility of achieving cross-phase charge balancing and simultaneously the possibility of single-phase loading by separately forming a neutral point that can be normally loaded by the load.

[0078] In an improvement of the present invention, it can be provided that each configurable DC voltage string has an output-side interface for providing the generated AC voltage, and has a cascade of multiple inverter units, which together can provide the AC voltage at the output-side interface.

[0079] Each inverter unit is preferably configured to include at least one DC voltage source that can be connected to the corresponding inverter unit during the generation of the AC voltage, or does not include a DC voltage source during the generation of the AC voltage.

[0080] The connection between the inverter unit and the DC voltage source can be realized, for example, by appropriate power supply lines and / or busbars.

[0081] An inverter based on the cascading of multiple inverter units is also called a "modular inverter". Using this technology, individual DC voltage sources are not directly connected in series, but are connected through individual inverter units, such as the power electronic H-bridge mentioned below.

[0082] Since each DC voltage source can be switched on or off through a separate inverter unit, charge equalization between the DC voltage sources, i.e., charge equalization between multiple battery cells, is possible. In the event of a fault in a DC voltage source, the inverter can also continue to operate using the DC voltage sources that are still operational. The availability of the energy supply system can thus be much higher than that of the traditional technology of directly connecting DC voltage sources in series. A defective DC voltage source (such as a defective battery cell) can be cut off and bypassed. More importantly, this also enables these DC voltage sources to be safely replaced even during operation.

[0083] In an advantageous manner, DC voltage sources with different usage times or states and different types can be used in the same energy supply system. For example, this can significantly extend the service life of the battery block.

[0084] In an advantageous refinement of the present invention, it can be stipulated that each inverter unit has an H-bridge circuit composed of four configurable power electronic switching elements.

[0085] Such an H-bridge circuit is basically known (see also "cascaded H-bridge"). For example, in this regard, reference should be made to DE 10 2018 003 642 A1, the disclosure of which is incorporated herein by reference in its entirety. The present invention is particularly advantageously applicable to inverters based on cascaded H-bridges. This is because in this way, the interconnection of the DC voltage sources can be advantageously adapted to charge equalization.

[0086] For example, two of the above-mentioned power electronic switching elements can each form a series circuit through their output connections and can each form a common connection branch of the H-bridge circuit. Two such connection branches can be provided. In the two connection branches, an output of the inverter unit can be respectively connected between the power electronic switching elements. The ends of the connection branches can be connected to each other, and the input of the inverter unit is connected to the ends; thus, the two connection branches can be connected in parallel.

[0087] It can be stipulated that the configurable power electronic switching element is designed as a bipolar transistor or, preferably, as a MOSFET. However, in principle, any switching element can be used, especially semiconductor elements. The configurable power electronic switching element can also be designed as a relay. The design of the configurable power electronic switching element basically does not limit the present invention.

[0088] The power electronic switching element can be configured, for example, by the aforementioned open-loop control device and / or open-loop control module. It can be set that the open-loop control device is configured to include a separate DC voltage source in the generation of the AC voltage or at least temporarily exclude the separate DC voltage source according to the status information transmitted by the open-loop control module to the DC voltage source.

[0089] The DC voltage source can be temporarily excluded, especially during charge equalization or for other reasons. For example, it can also be configured to permanently exclude a faulty or overheated DC voltage source. In particular, a deeply discharged battery can also be excluded in the long term.

[0090] In an advantageous refinement of the present invention, it can be stipulated that the neutral earthing transformer has a transformer.

[0091] The transformer can have, for example, a star-delta circuit, a zigzag circuit or other suitable interconnections to form a neutral point.

[0092] In an advantageous refinement of the present invention, it can be stipulated that the neutral earthing transformer is designed for a maximum load of less than 10 kW, preferably less than 8 kW, and particularly preferably less than 5 kW.

[0093] It may be sufficient to dimension the neutral earthing transformer (e.g., the transformer) only for a limited power limit value. The technical and economic requirements for providing the neutral earthing transformer can be adapted to, for example, the standards of individual countries or the intended applications. For example, in any case, the sum of all single-phase loads in the customer network usually must not exceed a certain limit value - for example, 4.6 kW in Germany and 3.7 kW in Austria.

[0094] If the nominal power of the DC voltage source or the energy storage device is much higher than these limit values, it may be particularly advantageous to dimension the neutral earthing transformer with respect to these limit values (i.e., for example, the limit values of 4.6 kW or 3.7 kW).

[0095] The present invention also relates to an energy supply system having a circuit device according to the above embodiments and the following embodiments and a DC voltage source. The DC voltage source is connected to the corresponding configurable DC voltage string.

[0096] In the proposed energy supply system, the DC voltage sources in the corresponding DC voltage strings can thus be distributed among the phases in the delta circuit. For example, a transformer in a star-delta circuit or a zigzag circuit can be used to implement the "missing" neutral point. Thus, the three-phase loads (i.e., the current components in the so-called positive phase sequence system and negative phase sequence system) are automatically taken over by the DC voltage sources (i.e., for example, taken over by an energy storage device containing DC voltage sources). The single-phase loads (i.e., the current in the so-called zero phase sequence system) can be automatically taken over by a neutral-grounded transformer or a transformer, since this current component can flow through the neutral-grounded transformer and its neutral point.

[0097] A particularly advantageous application of the proposed energy supply system relates to the power supply of electrical loads in electric vehicles, especially electric cars.

[0098] In an improvement of the present invention, it can be provided that the DC voltage source is designed as a battery cell of a battery.

[0099] The present invention also relates to an electrical load device, especially an electric vehicle, which has an energy supply system according to the above and following embodiments and at least one electrical load.

[0100] One load or multiple loads can be connected or connected to the output-side interface of the energy supply system. The load can be any electrical load to a group of multiple electrical loads. Preferably, the load is a motor, a drive unit, and / or at least one electrical load within a low-voltage network (especially a domestic power supply system).

[0101] In principle, the electrical load device can be any load device having at least one electrical load. For example, the load configuration can be an electromechanical tool, which can channel a building that requires electrical energy supply.

[0102] Particularly preferably, the electrical load device is an electric vehicle. The term "electric vehicle" refers to any electric means of transportation, especially vehicles for land, water, or air, including spacecraft. However, preferably, the electric vehicle or load device is an electric car.

[0103] However, the present invention is also particularly applicable to the power supply of households or factories.

[0104] The features described in connection with one of the subjects of the present invention, especially the features given by the method according to the present invention, the circuit device according to the present invention, the energy supply system according to the present invention, the load device according to the present invention, and the computer program according to the present invention, can also be advantageously implemented for other subjects of the present invention. Similarly, the advantages described in connection with one subject of the present invention can also be understood in connection with other subjects of the present invention.

[0105] In addition, it should be noted that expressions such as "comprising", "having" or "including" do not exclude any other features or steps. Further, expressions such as "a" or "the" referring to a step or feature in the singular do not exclude a plurality of features or steps, and vice versa.

[0106] However, in a pure embodiment of the present invention, it may also be stipulated that the features introduced in the present invention by the expressions "comprising", "having" or "including" constitute an exhaustive list. Thus, in the context of the present invention, one or more lists of features may be considered in an independent form, for example, respectively for each claim. For example, the present invention may include only the features specified in the claims.

[0107] Note that terms such as "first" or "second" are mainly used to distinguish between individual device or method features and do not necessarily imply that these features are interdependent or related to each other.

[0108] In this regard, it should be noted that the expressions "connected" or "connection" used in this specification and the claims may describe a direct electrical connection of the components or an indirect electrical connection of the components (i.e., for example, via additional wires or electronic components such as resistors, inductors and / or capacitors, etc.). On the other hand, the term "attached" generally represents a direct connection of the components.

[0109] Furthermore, it should be emphasized that the values and parameters described in the present case also include deviations or fluctuations of ±10% or less, preferably ±5% or less, more preferably ±1% or less, very particularly preferably ±0.1% or less of the respectively stated values or parameters, provided that these deviations are not excluded in practice when implementing the present invention. The specification of a range by a starting value and an end value also includes all values and fractions included by the respective range, in particular the starting value and the end value and the respective average value.

[0110] Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0111] Each drawing shows a preferred exemplary embodiment in which the various features of the present invention are shown in combination with each other. The features of an exemplary embodiment can also be implemented separately from other features of the same exemplary embodiment and can thus be easily combined by those skilled in the art to form further useful combinations and sub - combinations with the features of other exemplary embodiments.

[0112] In the drawings, elements having the same function are denoted by the same reference numerals. Description of the Drawings

[0113] In the drawings, in each case schematically:

[0114] Figure 1 Shows an energy supply system according to a first exemplary embodiment of the present invention, the energy supply system having a circuit device for generating three-phase alternating current from three configurable DC voltage strings connected in a delta circuit, wherein the transformer is a separate neutral-grounded transformer;

[0115] Figure 2 Shows an energy supply system according to a second exemplary embodiment of the present invention, the energy supply system having a circuit device for generating three-phase alternating current from three configurable DC voltage strings connected in a delta circuit, wherein the transformer is a separate neutral-grounded transformer;

[0116] Figure 3 Shows the H-bridge circuit of an exemplary inverter unit of a configurable DC voltage string;

[0117] Figure 4 Shows a closed-loop control method according to a first variant;

[0118] Figure 5 Shows a closed-loop control method according to a second variant;

[0119] Figure 6 Shows a closed-loop control method according to a third variant; and

[0120] Figure 7 Shows a closed-loop control method according to a fourth variant. Detailed Description of the Invention

[0121] Figure 1 and Figure 2 Shows two exemplary embodiments of the proposed energy supply system 1. The energy supply system 1 provides three-phase alternating current and thus has three phases L1, L2 and L3 and a neutral wire or neutral point N. The energy supply system 1 can be part of, for example, an electric vehicle (in particular part of an electric car) in order to supply electrical loads of the electric vehicle (in particular an electric motor, more precisely an AC or three-phase motor). However, in principle, it can be any energy supply system 1 for supplying electrical energy to any electrical load, i.e. for example also a domestic power supply system.

[0122] The energy supply system 1 has a circuit device 2 and a plurality of DC voltage sources 3. In the exemplary embodiment, the DC voltage sources 3 are part of a common energy storage component not shown in detail. The energy storage component is preferably a battery or rechargeable battery pack, wherein the individual DC voltage sources 3 can be designed as battery cells of the battery pack or rechargeable battery cells of the rechargeable battery pack. In particular, the DC voltage source 3 can be a battery cell of a high-voltage storage device of an electric vehicle or a domestic storage device.

[0123] The energy supply system 1 or the circuit arrangement 2 can have one or preferably a plurality of open-loop control units for determining status information relating to the battery cells 3. The status information can in particular be information about the current battery cell voltage, the current temperature, the current state of charge or the current "state of health" of the respective battery cell 3. Exemplary embodiments show a single central open-loop control device 4, which, however, should only be understood as an example.

[0124] The DC voltage source 3 or the battery cells are divided into three configurable DC voltage strings 5 such that for each DC voltage string 5 there is a configurable series circuit of the DC voltage source 3 or the battery cells. Each DC voltage string 5 is assigned to one of the three phases L1, L2, L3 and has an output-side interface 6 to which the respective AC voltages u L1 (t), u L2 (t), u L3 (t) are applied. The DC voltage strings 5 are arranged in a common delta circuit.

[0125] Each configurable DC voltage string 5 has a cascade of a plurality of inverter units 7 which together can provide the respective AC voltages u L1 (t), u L2 (t), u L3 (t) at the output-side interface 6. Each of these inverter units 7 is configured to include the DC voltage source 3 which can be connected to the respective inverter unit 7 during the generation of the AC voltages u L1 (t), u L2 (t), u L3 (t), or not to include the DC voltage source 3 during the generation of the AC voltages u L1 (t), u L2 (t), u L3 (t).

[0126] The open-loop control device 4 can accordingly be configured to configure the inverter units 7 such that the output-side AC voltages u L1 (t), u L2 (t), u L3 (t) correspond to the desired specifications in terms of amplitude, phase and / or frequency. Thus, by appropriately configuring the interconnection of the respective DC voltage sources 3 of the individual configurable DC voltage strings 5, a symmetric three-phase alternating current can generally be provided.

[0127] It is possible to provide a computer program including open-loop control instructions which, when executed by the open-loop control device 4, cause the open-loop control device 4 to perform the generation of the AC voltages u L1 (t), u L2(t), u L3 (t) or a corresponding method for polyphase alternating current.

[0128] As an example, Figure 3 the possible structure of a single inverter unit 7 is shown. The inverter unit 7 can particularly have an H-bridge circuit respectively, which includes four power electronic switching elements 8, and these switching elements can be configured by an open-loop control device 4. The open-loop control device 4 is also shown as an example in Figure 3 . The power electronic switching elements 8 can be particularly designed as semiconductor components, such as Figure 3 the MOSFET shown. The open-loop control device 4 can be designed to control the switching elements 8. The inverter unit 7 can ultimately be connected to a specified DC voltage source 3 through a corresponding power supply line 9. Those skilled in the art should know the corresponding H-bridge circuit, and more details will not be discussed in detail here.

[0129] The circuit device 2 or the energy supply system 1 also has a neutral grounding transformer 10, which is used to realize the common neutral point N of all configurable DC voltage strings 5. A (small) transformer with a star-delta circuit (see Figure 1 ) or a zigzag circuit (see Figure 2 ) can be advantageously used for this purpose. For a maximum load of less than 10 kW, preferably less than 8 kW, and particularly preferably less than 5 kW, designing the neutral grounding transformer 10 (i.e., for example, the transformer) may be sufficient.

[0130] The open-loop control device 4 is set to configure the DC voltage string 5 so that on the one hand, the charge of the DC voltage sources 3 in the same DC voltage string 5 is balanced as much as possible, and on the other hand, a desired RMS value I0 and a phase angle of the zero-sequence system current between the DC voltage strings 5 with different phases L1, L2, L3 are formed I 0 = I d0 + I q0 , so as to also be able to achieve cross-phase charge balance. The zero-sequence system current is the same in amplitude and phase in each configurable DC voltage string 5, and can be generated by a zero-sequence system voltage with an amplitude and a phase angle according to . In addition to the individual AC voltages u L1 (t), u L2 (t), u L3 (t), the zero-sequence system voltage can be set by appropriately interconnecting the DC voltage sources 3. In this case, the following relationship can be provided:

[0131]

[0132] and

[0133]

[0134] wherein, is the d component of the zero-sequence system voltage, is the q component.

[0135] Therefore, the following formulas can be applied to the alternating current of each phase L1, L2, L3:

[0136]

[0137] and

[0138]

[0139] wherein, the d component of the zero-sequence system current I d0 and the q component I q0 , and I which is the amplitude of the positive-sequence system current of phases L1, L2 and L3 and

[0140] Preferably, charge balancing can be achieved by one of the following two variants:

[0141] a) The phase with the lowest charge receives charge from the other two phases. In this case, the power of the phase with the lowest charge in the load reference arrow system is positive, that is, this phase consumes active power. The current component I d0 is positive; or

[0142] b) The phase with the highest charge supplies charge to the other two phases. In this case, the power of the phase with the highest charge in the load reference arrow system is negative, that is, this phase supplies active power. The current component I d0 is negative.

[0143] One or more closed-loop control methods can be used to determine the zero-sequence system current, wherein the zero-sequence system voltage is used as the manipulated variable, the target value of the zero-sequence system current is used as the reference variable, and the captured actual value of the zero-sequence system current is used as the closed-loop control variable. For example, the closed-loop control can be implemented as shown in Figure 4 or Figure 5. In the figure, I d0 * corresponds to the target value of the d current component I d0 , and I q0 * corresponds to the target value of the q current component I q0 .

[0144] The q-component I of the zero-sequence system current q0 It is preferably controlled to zero in a closed-loop manner to avoid reactive power loss. The target value of the d-component of the zero-sequence system current can also be determined considering the charge difference between the DC voltage sources 3 of the DC voltage string 5, preferably determined according to the proportional relationship with the charge difference.

[0145] Preferably, the closed-loop control structure to be used can be selected according to the ratio of the resistance and reactance of phases L1, L2, and L3. If the resistance R is greater than or equal to the reactance X, according to Figure 4 the closed-loop control may be more advantageous. On the contrary, if the reactance X is greater than the resistance R, then according to Figure 5 the closed-loop control may be more advantageous. In the battery storage device, due to the high ohmic internal resistance of the battery cells 3, the resistance R (far) is greater than the reactance X, and as a result R / X > 1, then according to Figure 4 the closed-loop control is preferred.

[0146] However, other alternatives for closed-loop control are also possible, such as closed-loop control according to the Figure 6 state or closed-loop control as shown in Figure 7 ​

Claims

1. A method for generating polyphase alternating current by interconnecting a plurality of DC voltage sources (3), the method having at least the following method steps: - Providing a configurable DC voltage string (5) for each phase (L1, L2, L3) of the polyphase alternating current, wherein each configurable DC voltage string (5) is formed by a plurality of DC voltage sources (3), and the DC voltage sources can be interconnected in a configurable series circuit; - Arranging the configurable DC voltage strings (5) in a polygon circuit; - Configuring the configurable DC voltage strings (5) such that polyphase alternating current is provided and a zero-sequence system current is also formed for charge balancing between the configurable DC voltage strings (5); Characterized in that the method further has at least the following method steps: - Providing a neutral grounding transformer (10) for realizing a common neutral point (N) of all configurable DC voltage strings (5); wherein, taking into account the charge difference between the DC voltage sources (3) of the DC voltage string (5), the q-component of the zero-sequence system current is minimized and / or the target value of the d-component of the zero-sequence system current is determined.

2. The method according to claim 1, wherein The polyphase alternating current is three-phase alternating current, and the polygon circuit is a triangle circuit.

3. The method according to claim 1, wherein Symmetrical three-phase alternating current is provided by appropriately configuring the interconnection of the respective DC voltage sources (3) of each configurable DC voltage string (5), and the following relationship applies to the AC voltage of each phase: Among them, the peak value is The network frequency is f.

4. The method according to any one of claims 1 to 3, characterized in that The zero-sequence system current in each configurable DC voltage string (5) is the same in magnitude and phase.

5. The method according to any one of claims 1 to 3, characterized in that, By appropriately configuring the interconnection of each DC voltage source (3) of each configurable DC voltage string (5) to form a zero-sequence system current and a zero-sequence system voltage, wherein according to the zero-sequence system voltage is applied to the AC voltage (u L1 (t), u L2 (t), u L3 (t)) of each phase (L1, L2, L3), wherein the amplitude of the zero-sequence system voltage is and the phase angle is 6. The method according to claim 5, characterized in that, One or more closed-loop control methods are used to determine the zero-sequence system current, wherein the zero-sequence system voltage is used as the manipulated variable, the target value of the zero-sequence system current is used as the reference variable, and the captured actual value of the zero-sequence system current is used as the closed-loop control variable.

7. The method according to any one of claims 1 to 3, characterized in that, The q-component of the zero-sequence system current is controlled to zero in a closed-loop manner.

8. The method according to any one of claims 1 to 3, characterized in that The target value of the d-component of the zero-sequence system current is determined according to the proportional relationship of the charge difference between the DC voltage sources (3) of the DC voltage string (5).

9. A computer program product comprising a computer program, the computer program comprising control instructions, which, when the computer program is executed by a control device (4), execute the method according to any one of claims 1 to 8.

10. A circuit device (2) for generating polyphase alternating current from a plurality of DC voltage sources (3), the circuit device (2) comprising - Configurable DC voltage strings (5) for each phase (L1, L2, L3) of the polyphase alternating current, wherein each configurable DC voltage string (5) is configured to interconnect a plurality of DC voltage sources (3) in a configurable series circuit, the DC voltage sources being connectable to the configurable DC voltage strings (5), and wherein the configurable DC voltage strings (5) are arranged in a polygon circuit; and - A control device (4) for configuring the configurable DC voltage strings (5) to provide polyphase alternating current and form a zero-sequence system current for charge balancing between the configurable DC voltage strings (5); Characterized in that A neutral earthing transformer (10) for implementing a common neutral point (N) of all configurable DC voltage strings (5), wherein the control device (4) is configured to minimize the q-component of the zero-sequence system current and / or determine a target value of the d-component of the zero-sequence system current taking into account the charge difference between the DC voltage sources (3) of the DC voltage strings (5).

11. The circuit device (2) according to claim 10, characterized in that, The polyphase alternating current is three-phase alternating current, and the polygonal circuit is a triangular circuit.

12. The circuit device (2) according to claim 10 or 11, characterized in that, Each configurable DC voltage string (5) has an output-side interface (6) for providing the generated AC voltage (u L1 (t), u L2 (t), u L3 (t)), and has a cascade of a plurality of inverter units (7), the plurality of inverter units (7) together being able to provide an AC voltage (u L1 (t), u L2 (t), u L3 (t)) at the output-side interface (6), wherein each inverter unit (7) is configured to include at least one DC voltage source (3) during the generation of the AC voltage (u L1 (t), u L2 (t), u L3 (t)), the DC voltage source being connectable to the corresponding inverter unit (7), or not including a DC voltage source during the generation of the AC voltage (u L1 (t), u L2 (t), u L3 (t)).

13. The circuit device (2) according to claim 12, characterized in that, Each inverter unit (7) has an H-bridge circuit composed of four configurable power electronic switching elements (8).

14. The circuit device (2) according to claim 10 or 11, characterized in that, The neutral earthing transformer (10) has a transformer with a star-delta or zigzag circuit.

15. The circuit device (2) according to claim 10 or 11, characterized in that, The neutral earthing transformer (10) is designed for a maximum load of less than 10 kW.

16. The circuit arrangement (2) according to claim 10 or 11, characterized in that, The neutral earthing transformer (10) is designed for a maximum load of less than 8 kW.

17. The circuit arrangement (2) according to claim 10 or 11, characterized in that The neutral earthing transformer (10) is designed for a maximum load of less than 5 kW.

18. An energy supply system (1) having a circuit arrangement (2) according to any one of claims 10 to 17 and a DC voltage source (3), wherein the DC voltage source (3) is connected to a respective configurable DC voltage string (5).

19. The energy supply system (1) according to claim 18, characterized in that, The DC voltage source (3) is designed as a battery cell of a battery.

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