ENERGY SUPPLY SYSTEM AND METHOD FOR CHARGING A ENERGY SUPPLY SYSTEM

Description

[0001] The invention relates to an energy supply system and a method for charging an energy supply system.

[0002] Combustion engines are predominantly used today to power mobile, high-performance machines and vehicles, especially those with an output power of over 1 kW. To reduce environmental and health impacts from exhaust gases and noise, such energy supply systems are increasingly being replaced by battery-based energy storage systems.

[0003] For many applications, it is advantageous if such a power supply system can provide an alternating voltage. Examples include loads suitable for operation with standard AC mains voltage or electric motors such as three-phase asynchronous motors. Furthermore, for high-power loads, it is desirable to provide the highest possible supply voltage in order to minimize the required operating currents and thus also electrical losses.

[0004] To generate such an alternating voltage from the direct current of a battery storage system, an electrical converter is required. Today, so-called two- or three-level inverters are almost exclusively used for this purpose. These inverters generate a single- or three-phase, sinusoidal output voltage from an intermediate circuit voltage (battery voltage) by chopping and smoothing.

[0005] US 3867643 A describes an alternative electrical converter in which multi-level conversion occurs. A plurality of DC sources, such as batteries, are periodically connected in series to the current path or bridged by a bridge circuit, so that the resulting output voltage assumes an approximately sinusoidal waveform. US 5642275 A describes the implementation of this converter technology with battery modules, with each battery module having at least one DC source and a bridge circuit. Such converters are often referred to in the literature as "cascaded multilevel inverter / converter" or "modular multilevel inverter / converter." Converters of this type have proven advantageous over two- or three-level converters, particularly with regard to cost, thermal losses, and size.

[0006] EP 3 014 725 B1 describes a similar system with a battery direct converter. Since a battery direct converter is not available as a DC voltage source, for example, to supply a vehicle's electrical system, a module tap circuit is provided that selectively feeds a portion of the energy storage modules to a DC voltage collector. This circuit can also be used to charge the energy storage modules.

[0007] The maximum charging voltage that can be drawn from a power supply system with a corresponding design depends, among other things, on the number and size of the battery modules. Overvoltage can lead to damage to the battery modules.

[0008] US 7 589 499 B2 discloses a protection circuit for protecting a rechargeable battery from overvoltage transients, particularly in portable electronic devices such as laptops, PDAs or smartphones.

[0009] The invention is based on the object of providing a power supply system with a cascaded multilevel inverter / converter that can be charged from a supply grid that provides an alternating current with a peak voltage that is too high for the battery modules of the power supply system. The invention is further based on the object of providing a method for charging a power supply system with a cascaded multilevel inverter / converter that allows the power supply system to be charged from a supply grid that provides an alternating current with a peak voltage that is too high for the battery modules of the power supply system.

[0010] The objects are achieved by specifying the energy supply system according to claim 1 and the method for charging an energy supply system according to claim 13. The subclaims relate to various independent, advantageous developments of the present invention, the features of which can be freely combined with one another by the person skilled in the art within the scope of what is technically reasonable, in particular also across the different claim categories.

[0011] A first aspect of the invention relates to an energy supply system having a plurality of battery modules, wherein each battery module has a first electrical connection and a second electrical connection, via which the battery modules are arranged in series in a circuit branch of the energy supply system, wherein each battery module further has an accumulator which can be connected to the first electrical connection and the second electrical connection via a bridge circuit of the battery module, wherein the energy supply system has a switch arranged in series with the battery modules, which switch can be temporarily put into a blocking state so that during a charging process of the energy supply system with an alternating voltage from an external energy source, a load voltage in the circuit branch does not exceed a maximum permissible charging voltage.

[0012] If the energy supply system is thus subjected to a voltage that exceeds the maximum permissible charging voltage, the switch is put into the off state. This prevents the battery modules from being subjected to a voltage for which they may not be designed. The bridge circuit can basically be any type of bridge circuit. With the aid of the bridge circuit, it is preferably possible to connect the accumulator to the connection branch in different ways. For example, the invention provides for the battery module to be connected with different polarities, or for the battery module to be bridged by means of the bridge circuit. By suitable control of the bridge circuits, the energy supply system can provide an alternating voltage.According to one variant of the invention, the maximum permissible charging voltage can be a predefined, fixed voltage value; however, it is alternatively possible for it to be a variable value that is continuously adjusted during operation of the energy supply system. For example, the maximum permissible charging voltage can depend on the charge levels of the accumulators in the battery modules. For this purpose, the battery modules can, according to the invention, have voltage measuring devices that can monitor the charge levels of the accumulators. The energy supply system is preferably quite compact. Thus, it is preferably a portable / mobile energy supply system that can be used variably, for example, on construction sites, to provide electrical energy.

[0013] According to the invention, it is possible for the energy supply system to have a control unit configured to place the switch in the off state as soon as the load voltage exceeds the maximum permissible charging voltage. The control unit can be coupled to at least one voltmeter, at least one current meter, and / or other sensors. Based on a measured voltage and optionally based on other values, the control unit can decide whether the switch should be placed in the off state. According to the invention, the control unit can also be used to control the bridge circuits of the battery modules and / or other components of the energy supply system.

[0014] It is advantageous if the control unit is configured to switch the switch from the blocking state to a non-blocking state during the charging process as soon as the circuit branch is subjected to a voltage so high that the load voltage after the switch is placed in the non-blocking state is lower than the maximum permissible charging voltage of the energy supply system. According to the invention, the energy supply system can be charged with an alternating voltage. A supplied voltage will generally rise and fall again in a sinusoidal manner. After the maximum charging voltage is exceeded, the supplied voltage generally continues to rise, then reaches a peak and falls again.At a certain point, the voltage is so low again that, once the switch is set to the non-blocking state, the load voltage applied to the battery modules would be lower than the maximum permissible charging voltage of the power supply system. At this point, the switch is set back to the non-blocking state, so that the battery modules are supplied with voltage again and the accumulators in the battery modules are charged. The voltage in the circuit branch that can be measured for this purpose can, for example, be a voltage measured across the battery modules and the switch.This voltage or another measured value can alternatively be measured at another point in the circuit branch or at another point in the power supply system in order to determine whether the load voltage would actually be lower than the maximum permissible charging voltage after the switch is placed in the non-blocking state.

[0015] According to the invention, the load voltage is a voltage applied to the battery modules in the circuit branch or an amount of the voltage applied to the battery modules in the circuit branch. The load voltage is accordingly a voltage to which the battery modules in the circuit circuit are subjected in total. The load voltage is preferably determined with the aid of a voltmeter that measures a voltage in the circuit across both the battery modules and the switch. A voltage drop across the switch can be taken into account in a suitable manner in order to calculate the actual load voltage on the battery modules. For example, a voltage drop typically across the switch can be subtracted from a measured voltage to obtain the load voltage.If the voltage drop across the switch is very low, according to embodiments of the invention, this can also be completely neglected when determining the load voltage. According to the invention, a voltmeter can be connected directly upstream of the battery modules and the switch. However, it is also possible for the energy supply system to have means for measuring a voltage and / or a current elsewhere in the energy supply system and to be configured to derive the load voltage therefrom. It is understood that the load voltage can be an amount of voltage applied to the battery modules. Thus, it is irrelevant whether the battery modules are subjected to a positive or a negative voltage of a certain amount.

[0016] The switch is preferably designed so that it can block at least a voltage equal to the difference between an expected maximum load voltage in the circuit branch and a minimum maximum permissible charging voltage. The maximum permissible charging voltage can depend on the charge states of the accumulators in the battery modules, i.e., it can change during operation, which is why the minimum maximum charging voltage must be used in this case. The battery modules can be charged with a maximum of the minimum maximum charging voltage if their module voltages each assume a minimum expected value. At the minimum maximum charging voltage, the greatest possible voltage difference results, which must be blocked by the switch.For example, if it is expected that a power supply system could be connected to a power grid with a maximum peak voltage of V 1 , but the power supply system is only designed for a minimum maximum permissible loading voltage V 2 that is less than V 1 , then the switch must be able to block a voltage in the range of V 1 - V 2 . It is even better if the switch is designed to be able to block at least an expected maximum load voltage in the interconnection branch. For example, if it is expected that the power supply system could be connected to a power grid with a peak voltage of V 3 , then the switch should preferably be suitable for completely blocking the voltage V 3 .

[0017] It is advantageous if the power supply system has a voltmeter arranged on the input side of the switch for measuring the load voltage. The voltmeter is preferably coupled to the previously described control unit and is designed to measure the peak voltage. The voltmeter can be arranged directly in the circuit branch or further upstream of the switch within the power supply system.

[0018] According to the invention, it is possible for the switch to be designed such that it blocks current flow unidirectionally in the off state. Alternatively, however, the switch can also be designed such that it blocks current flow bidirectionally in the off state. The choice of a suitable switch is determined in particular by the intended charging mode and the expected peak voltage that the power supply system could be subjected to during a charging process.

[0019] It is preferred if the power supply system has a rectifier bridge arranged on the input side of the switch. The rectifier bridge ensures that current can only flow in one direction. Thus, a bidirectional blocking switch can be dispensed with. It is therefore particularly preferred if the power supply system has a unidirectional blocking switch, and the rectifier bridge is connected upstream of this switch on the input side.

[0020] According to the invention, it is possible for the switch to be a transistor. The transistor can be, for example, a MOSFET (metal oxide semiconductor field-effect transistor) or an IGBT (insulated gate bipolar transistor). Alternatively, the switch can also be designed as a TRIAC (bidirectional thyristor triode) or an SCR (controlled silicon rectifier). However, the switch can also be designed as a switching module of another type.

[0021] According to an advantageous embodiment of the invention, the switch in the circuit branch is arranged upstream of a first battery module of the battery modules or downstream of a last battery module of the battery modules. Thus, the switch is not arranged between two battery modules. It is further possible according to the invention for the circuit branch to have a resistor connected in parallel with the switch. Otherwise, when the switch is closed, an overvoltage could build up at the switch due to inductive effects. The resistor connected in parallel counteracts this, as a current can flow through it.

[0022] It is preferred if the energy supply system is configured to check electrical energy provided to the energy supply system by the external energy source for the presence of at least one fault characteristic and to switch itself off upon detection of the fault characteristic. By monitoring suitable parameters, fault conditions can be avoided, for example, an unintentional feeding of electrical energy back into a supply network. It is particularly preferred if the fault characteristic is selected from the group comprising the presence of an overcurrent, the presence of an overvoltage, the presence of an undervoltage, an interruption of a connection to an external energy source due to a plug being pulled out, an exceeding of a voltage rise rate, an exceeding of a voltage fall rate, and an exceeding or falling below of a voltage frequency.

[0023] It is advantageous if the bridge circuit is a full bridge. This allows for maximum flexibility in connecting the battery to the circuit branch. Alternatively, however, the bridge circuit can also be a half bridge or have a different configuration.

[0024] According to a preferred embodiment of the invention, the energy supply system has a switching means to which the circuit branch is connected, wherein the energy supply system further has a charging path and a discharging path, which are connected to the switching means and between which the switching means can switch, and wherein the switch is arranged in the charging path. Electrical energy can be supplied to the energy supply system via the charging path in order to charge the batteries. The energy supply system can provide electrical energy to a consumer via the discharging path. With the aid of the switching means, either the charging path or the discharging path can be electrically conductively connected to the circuit branch in a simple manner. The switching means preferably has one or more relays. The rectifier bridge described above can preferably also be arranged in the charging path.Furthermore, it is advantageous if the voltage measuring device described above is arranged in the charging path.

[0025] According to the invention, it is further possible for the power supply system to be configured to de-energize the switch before switching it into the off-state by having the bridge circuits assume suitable switching states for this purpose. In this way, overloading of the switch can be avoided if it is suddenly to be switched into the off-state. To ensure that the switch is actually de-energized, a current measuring device can be arranged in the circuit branch according to the invention. According to the invention, switching the switch into the off-state can be delayed until the switch is actually de-energized.Preferably, the power supply system is configured to continuously increase the current applied to the switch during and immediately after the switch is placed in a non-blocking state from a zero level to an operating level by having the bridge circuits assume suitable switching states. This prevents the current from rising too quickly or the dI / dt from becoming too high, which could lead to overloading of the switch. An excessively high dI / dt value could also lead to conducted interference, which could affect a supply network to which the power supply system is connected.

[0026] According to a further aspect of the invention, a method for charging an energy supply system with an alternating voltage is proposed, wherein the energy supply system has a plurality of battery modules, wherein each battery module has a first electrical connection and a second electrical connection, via which the battery modules are arranged in series in a circuit branch of the energy supply system, wherein each battery module further has an accumulator which can be connected to the first electrical connection and the second electrical connection via a bridge circuit of the battery module, and wherein the energy supply system temporarily puts a switch arranged in series with the battery modules into a blocking state so that a load voltage in the circuit branch does not exceed a maximum permissible charging voltage.This prevents the battery modules from being subjected to excessive voltage.

[0027] It is advantageous if, when carrying out the method, a control unit of the energy supply system sets the switch to the blocking state as soon as the load voltage exceeds the maximum permissible charging voltage. According to the invention, the control unit can monitor the load voltage using a voltage measuring device of the energy supply system. According to the invention, the method can further be carried out such that, during the charging process, the control unit sets the switch from the blocking state to a non-blocking state as soon as the circuit branch is subjected to a voltage that is so great that the load voltage, after setting the switch to the non-blocking state, is lower than the maximum permissible charging voltage of the energy supply system.If the voltage drops to such an extent that the load voltage would be below the maximum permissible charging voltage after the switch is placed in the non-blocking state, the batteries can therefore be charged again.

[0028] According to the invention, it is possible for the switch to be de-energized before being placed in the off-state by the bridge circuits assuming suitable switching states for this purpose. As described above, this can prevent overloading of the switch. Furthermore, a current applied to the switch during and immediately after the switch is placed in a non-off state is preferably continuously increased from a zero level to an operating level by the bridge circuits assuming suitable switching states for this purpose. This is advantageous because it can prevent an excessively rapid increase in the current in the power supply system. Otherwise, this could lead to overload effects and disruptions in a connected supply network.

[0029] Advantageous variants of the invention are illustrated by way of example in the drawings. Herein: Fig. 1 a schematic representation of an energy supply system according to the invention, Fig. 2 a schematic representation of a battery module of the battery arrangement according to Fig. 1 , Fig. 3 a schematic representation of a bridge circuit of the battery module according to Fig. 2 , Fig. 4 a schematic representation of a unidirectional blocking switch, Fig. 5 a schematic representation of a bidirectional blocking switch, Fig. 6 a diagram of a current and a voltage curve over time when carrying out the method according to the invention and Fig. 7 a schematic representation of a variant of the energy supply system according to the invention.

[0030] Fig. 1shows a schematic representation of an energy supply system 1 according to the invention. A plurality of battery modules 2 are arranged in the energy supply system 1. These are connected in series in a circuit branch 9. A first battery module 13 and a last battery module 14 are identified separately here. Each battery module 2 has a first electrical connection 3 and a second electrical connection 4, via which the respective battery module 2 is connected to the circuit branch 9. A control unit 11 controls the battery modules 2 in a suitable manner during a discharging process so that their voltages add up to an approximately sinusoidal alternating voltage. During a charging process, the control unit 11 controls the battery modules 2 such that the accumulators of the battery modules 2 are always connected to a voltage of the correct polarity and can thus be charged.

[0031] A coil 20, a voltmeter 18, and a current meter 19 are arranged in the circuit branch 9. Furthermore, a switch 10 is arranged in the circuit branch 9, which is connected upstream of the last battery module 14 on the input side. The voltmeter 18, in turn, is connected upstream of the switch 10 on the input side. The control unit 11 sets the switch 10 to a blocking state as soon as a load voltage determined by the voltmeter 18 exceeds a maximum permissible charging voltage. This prevents the battery modules 2 from being subjected to an impermissibly high voltage, which could damage them.

[0032] Fig. 2 shows a schematic representation of one of the battery modules 2 of the energy supply system according to Fig. 1The battery module 2 has an accumulator 5 that can be electrically charged and discharged. The battery module 2 further has a bridge circuit 6 that is connected to the first electrical terminal 3 and the second electrical terminal 4 of the battery module 2. The bridge circuit 6 can assume different switching states. For example, it can change the polarity with which the first electrical terminal 3 and the second electrical terminal 4 are connected to an inner branch 21 of the battery module 2. The bridge circuit 6 can also bridge the inner branch 21. By appropriately changing the switching states, a plurality of battery modules 2 arranged in series can thus provide an alternating voltage. Furthermore, it is possible to charge the accumulator 5. The battery module 2 also has an insulation device 22.This galvanically separates an interior of the battery module 2 from a control terminal 23 of the battery module 2 and contains an optocoupler for this purpose.

[0033] A bridge controller 24 receives a signal generated by the control device, which indicates a desired switching state. This signal is fed to the bridge controller 24 from the control terminal 23 via the isolation device 22. Depending on the signal, the bridge controller 24 controls the bridge circuit 6 such that the switching state specified by the signal is established. A capacitor 25 is arranged in the inner branch 21. A disconnecting device 26 in the inner branch 21 allows the accumulator 5 to be disconnected from the inner branch 21 if necessary. Furthermore, a fuse 27 is arranged in the inner branch 21, which disconnects the accumulator 5 from the inner branch 21 in the event of an overcurrent.

[0034] Fig. 3shows a schematic representation of the bridge circuit 6 of the battery module according to Fig. 2 This is a full bridge, allowing a wide variety of switching states. However, according to other embodiments of the invention, a half bridge can also be used.

[0035] Fig. 4 shows a schematic representation of a unidirectional blocking switch 10. This allows current to flow in one direction even when in a blocking state. The switch 10 is formed by a MOSFET with diode behavior. A resistor 15 is connected in parallel with the switch 10. The resistor 15 serves to prevent an overvoltage at the switch 10 when the switch 10 is switched from a non-blocking state to a blocking state.

[0036] Fig. 5shows a schematic representation of a bidirectionally blocking switch 10. In a blocking state, this switch does not allow current to flow in either direction. The switch 10 is formed by two MOSFETs arranged in series, but with different drain and source orientations. A resistor 15 is connected in parallel with the switch 10. The resistor 15 serves to prevent an overvoltage at the switch 10 when the switch 10 is switched from a non-blocking state to a blocking state.

[0037] Fig. 6shows a diagram of a current and a voltage curve over time when carrying out the method according to the invention. A current curve 28 and a voltage curve 29 represent a current and a voltage curve over time. A voltage underlying the voltage curve 29 is measured by a voltmeter in the interconnection circuit, which measures a voltage across the switch and the battery modules. This voltage approximately corresponds to the load voltage when the switch of the energy supply system is in a non-blocking state. When the switch is in a blocking state, the load voltage ideally has a value of 0 V, and the voltage curve 29 simply represents the voltage value that the load voltage would assume if the switch were to be immediately switched to the non-blocking state.

[0038] The energy supply system is connected to a supply network that supplies the energy supply system with a sinusoidal alternating voltage according to voltage curve 29. Current curve 28 describes a current in the circuit branch of the energy supply device. However, voltage curve 29 has peak values ​​that exceed a maximum permissible charging voltage 12 to which the battery modules of the energy supply system may be subjected. The energy supply system therefore ensures that the load voltage is limited. For this purpose, the load voltage in the circuit branch is continuously measured. At a first time 30, the load voltage exceeds the maximum permissible charging voltage 12. The switch of the energy supply system is placed in a blocking state, and current flow according to current curve 28 ceases. Overstressing of the battery modules is avoided.At a second point in time, however, voltage curve 29 falls below the maximum permissible charging voltage, so the switch is switched to a non-blocking state. Current can now flow again, and the battery modules of the power supply system can continue to be charged. The described process repeats cyclically.

[0039] Fig. 7 shows a schematic representation of a variant of the energy supply system 1 according to the invention. Components arranged in a circuit branch 9 of the energy supply system 1 are represented abstractly by a module block 32. The structure contained therein is similar to that of Fig. 1, wherein the switch 10 of the energy supply system 1 is not included in the module block 32. The energy supply system 1 has a switching means 16 to which the circuit branch 9 is connected. The energy supply system 1 further has a charging path 7 and a discharging path 8, which are connected to the switching means 16 and between which the switching means 16 can switch. The switching means 16 has several relays by means of which it can switch between the charging path 7 and the discharging path 8. The switch 10 is arranged in the charging path 7. This design allows battery modules of the energy supply system to be optionally charged via the charging path 7 or discharged via the discharging path 8, so that electrical energy can be provided to a connected consumer. Furthermore, a rectifier bridge 17 is arranged in the charging path 7, which ensures that a current can only flow into the switch 10 in one direction. List of reference symbols

[0040] 1. Power supply system 2. Battery module 3. First electrical connection 4. Second electrical connection 5. Accumulator 6. Bridge circuit 7. Charging path 8. Discharge path 9. Connection branch 10. Switch 11. Control unit 12. Maximum permissible charging voltage 13. First battery module 14. Last battery module 15. Resistor 16. Switching device 17. Rectifier bridge 18. Voltmeter 19. Ammeter 20. Coil 21. Inner branch 22. Insulation device 23. Control connection 24. Bridge control 25. Capacitor 26. Disconnecting device 27. Fuse 28. Current curve 29. Voltage curve 30. First time 31. Second time 32. Module block

Claims

1. Power supply system (1) with a multiplicity of battery modules (2), wherein each battery module (2) has a first electrical terminal (3) and a second electrical terminal (4), by way of which the battery modules (2) are arranged in series in a circuit branch (9) of the power supply system (1), wherein each battery module (2) further comprises an accumulator (5) which can be connected to the first electrical terminal (3) and the second electrical terminal (4), by way of a bridge circuit (6) of the battery module (2), wherein the bridge circuit (6) is designed to connect the accumulator (5) with different polarity with the first and the second electrical terminal (3, 4) or to connect the first electrical terminal (3) and the second electrical terminal (4) to each other, wherein the power supply system (1) has a switch (10), which is arranged in series with the battery modules (2), and can be temporarily moved into a blocking state so that, during a charging process of the power supply system (1) with an AC voltage from an external energy source, a load voltage in the circuit branch (9) does not exceed a maximum permissible charging voltage (12) and that the load voltage is a voltage applied to the battery modules (2) in the circuit branch (9), or a proportion of the voltage applied to the battery modules (2) in the circuit branch (9).

2. Power supply system (1) according to Claim 1, characterised in that, the power supply system (1) has a control unit (11) which is set up to put the switch (10) into the blocking state as soon as the load voltage exceeds the maximum permissible charging voltage (12).

3. Power supply system (1) according to Claim 2, characterised in that, the control unit (11) is set up to move the switch (10) from the blocking state to a non-blocking state during the charging process as soon as a voltage is applied to the circuit branch (9), which is of a level such that the load voltage after moving the switch (10) into the non-blocking state is lower than the maximum permissible charging voltage (12) of the power supply system (1).

4. Power supply system (1) according to one of the preceding claims characterised in that, the switch (10) is designed to block at least a voltage equal to a difference between an anticipated maximum voltage in the circuit branch (9) and a minimum maximum permissible charging voltage or that the switch (10) is designed to block at least one anticipated maximum load voltage in the circuit branch (9).

5. Power supply system (1) according to one of the preceding claims, characterised in that, the power supply system has a voltage measuring device (18) arranged on the input side of the switch (10) for measuring the load voltage.

6. Power supply system (1) according to one of the preceding claims, characterised in that, the power supply system (1) has a rectifier bridge (17) arranged on the input side of the switch (10).

7. Power supply system (1) according to one of the preceding claims, characterised in that, the switch (10) is a transistor, a TRIAC or an SCR.

8. Power supply system (1) according to one of the preceding claims, characterised in that, the switch (10) is arranged in the circuit branch (9) in front of a first battery module (13) of the battery modules (2), or behind a last battery module (14) of the battery modules (2).

9. Power supply system (1) according to one of the preceding claims, characterised in that, the power supply system (1) is arranged to check electrical power provided by the external power source to the power supply system (1) for the presence of at least one fault characteristic, and to switch off upon detection of the fault characteristic, wherein the fault characteristic is preferably selected from the group comprising a presence of an overcurrent, a presence of an overvoltage, a presence of an undervoltage, an interruption of a connection to an external power source due to a disconnection of a plug, an exceedance of a slew rate of a voltage, an exceedance of a fall rate of a voltage, and an exceedance of, or a falling below, a voltage frequency.

10. Power supply system (1) according to one of the preceding claims, characterised in that, the power supply system (1) has a switching means (16) to which the circuit branch (9) is connected, wherein the power supply system (1) furthermore comprises a charging path (7) and a discharging path (8), which are connected to the switching means (16), and between which the switching means (16) can switch, and wherein the switch (10) is arranged in the charging path (7).

11. Power supply system (1) according to one of the preceding claims, characterised in that, the power supply system (1) is set up to de-energise the switch (10) before it is placed in the blocking state by the bridge circuits (6) assuming switching states suitable for this purpose.

12. Power supply system (1) according to one of the preceding claims, characterised in that, the power supply system (1) is adapted to raise continuously a current applied to the switch (10) from a zero level to an operating level during, and immediately after placing the switch (10) in a non-blocking state by the bridge circuits (6) assuming switching states suitable for this purpose.

13. Method for charging a power supply system (1) with an AC voltage, wherein the power supply system (1) comprises a multiplicity of battery modules (2), wherein each battery module (2) has a first electrical terminal (3) and a second electrical terminal (4), by way of which the battery modules (2) are arranged in series in a circuit branch (9) of the power supply system (1), wherein each battery module (2) further comprises an accumulator (5) which can be connected to the first electrical terminal (3) and the second electrical terminal (4) by way of a bridge circuit (6) of the battery module (2), wherein the bridge circuit (6) is designed to connect the accumulator (5) with different polarity with the first and the second electrical terminal (3, 4) or to connect the first electrical terminal (3) and the second electrical terminal (4) to each other, wherein the power supply system (1) temporarily puts a switch (10) arranged in series with the battery modules (2) into a blocking state during the charging process, so that a load voltage in the circuit branch (9) does not exceed a maximum permissible charging voltage (12), and wherein the load voltage is a voltage applied to the battery modules (2) in the circuit branch (9), or a proportion of the voltage applied to the battery modules (2) in the circuit branch (9).

14. Method according to Claim 13, characterised in that, a control unit (11) of the power supply system (1) sets the switch (10) to the blocking state as soon as the load voltage exceeds the maximum permissible charging voltage (12).

15. Method according to Claim 14, characterised in that, the control unit (11) shifts the switch (10) from the blocking state to a non-blocking state during the charging process as soon as a voltage is applied to the circuit branch (9) which is so high that the load voltage after moving the switch (10) to the non-blocking state is lower than the maximum permissible charging voltage (12) of the power supply system (1).