Power supply system with parallel supply units and master-slave operation

Abstract

A power supply system (10) according to the invention comprises a first power supply (1) and at least a second power supply (2), which are interconnected at the output end to form a parallel circuit in order to jointly feed a load (3). The first power supply (1) is designed to provide a first regulated output voltage (U1) and a first output current (I1) at the output end. The second power supply (2) is designed to provide a second regulated output voltage (U2) and a second output current (I2) at the output end. The power supply system (10) is designed here to regulate the first output voltage (U1) at a predefined or predefinable value independently of the first output current (I1), and to regulate the second output voltage (U2) in such a way that a difference between the first output current (I1) and the second output current (I2) is at least reduced, preferably to zero. Very good balancing of the load currents can be achieved in this way and in the process it is possible to ensure that the predefined or predefinable supply voltage is always provided for a load.

Description

[0001] Description

[0002] POWER SUPPLY SYSTEM WITH PARALLEL SUPPLY UNITS AND MASTER-SLAVE OPERATION

[0003] The invention relates to a power supply system comprising a first power supply and at least one second power supply, which feed a common load on the output side in a parallel circuit. The invention further relates to a method for operating a power supply system and to a power supply for use in such a power supply system or method.

[0004] In industrial automation technology (e.g. in discrete manufacturing technology or process technology) or in building automation, electronic power supplies are used on a large scale to supply electrical loads, such as controllers, sensors, pumps, valves, etc., with electrical energy from a supply network.

[0005] The loads are supplied with a suitable, often predefined voltage from the power supply. Typically, a high voltage level on the input side of a single-phase or three-phase supply network, such as 230 V AC, is converted to a lower, usually constant voltage level predefined for the load (e.g., 24 V or 48 V DC as the nominal output voltage) on the output side of the power supply.

[0006] Such power supplies are usually designed as clocked power supplies or switched-mode power supplies (sometimes also referred to as switching power supplies) and are known, for example, from EP 3544166 A1 and EP 3451476 A1.

[0007] They usually have a housing and can be mounted on a DIN rail. Such a switch-mode power supply or such a switched-mode power supply generally comprises an input stage, for example in the form of a rectifier unit, an intermediate circuit and a switching converter, which converts the alternating voltage from the mains supply into a direct voltage for supplying energy to the load. The power supply then converts the usually unstabilized input voltage into a constant output voltage for the electrical load, with a constancy of the output voltage and / or output current being achieved by regulating the energy flow.

[0008] Such power supplies sometimes also offer the option of connecting the outputs of two power supplies in parallel. This allows for higher output power to be provided. However, with such a parallel connection, care must be taken to ensure that the parallel-connected power supplies are operated with approximately the same load current, i.e., the load currents are "balanced." If this is not balanced, there is a risk that one of the power supplies will always be operated at a very high load or full load, which results in significantly higher operating temperatures and increased component stress, which can lead to a shortened service life and premature failure.

[0009] In order to ensure that the power supplies connected in parallel have the same load and therefore the same ageing behavior, it is known to operate the power supplies for parallel operation in an operating mode with "inclined" output characteristics. In this operating mode, the voltage at the output terminals of the power supply is reduced slightly in linear dependence on the load current. The higher the load current, the more the output voltage is reduced. When idle without a load, there is no reduction in the output voltage; at nominal load, the voltage is reduced by 1.2V for 24V devices and by 2V for 48V devices. The load-dependent reduction in the output voltage symmetrizes the load currents of the power supplies connected in parallel, but the user has the disadvantage of a non-constant supply voltage at his load.

[0010] EP 2 009 777 A2 discloses a switch-mode power supply comprising a first power section and a controller for regulating an output voltage and / or an output current as a function of a load connected on the output side and an input voltage applied on the input side, wherein a second power section forms a parallel circuit with the first power section such that a total output current of the power supply is composed of a first output current of the first power section and a second output current of the second power section. A main controller is provided for generating a first pulse-width modulated signal for controlling the first power section.Furthermore, a sub-controller is provided, to which the first pulse-width-modulated signal and a difference signal proportional to the difference between the first and second output currents are fed, and at whose output a second pulse-width-modulated signal for controlling the second power section can be tapped. This enables continuous adjustment of the first and second output currents. The first and second pulse-width-modulated signals directly control the respective power sections, i.e., they directly intervene in the on / off switching of a switching element of the respective power section.

[0011] US Pat. No. 6,141,231 A discloses a circuit and method for power distribution between parallel power supplies using a master / slave scheme. Each of the power supplies converts an input voltage into a regulated output voltage using internal control signals. A power supply acting as the master transmits its internal control signals to the other power supplies via a current-sharing bus. The other power supplies then use the master's internal control signals as their own internal control signals to convert their input voltage into an output voltage. This ensures good current distribution between the power supplies.

[0012] For further information on the state of the art, reference is made to US 2015 / 0012151 A1 and US 5,675,480 A.

[0013] Based on this, the object of the present invention is to achieve an equal load on power supplies connected in parallel and at the same time to avoid a load-dependent reduction of the output voltage.

[0014] This object is achieved by a power supply system according to patent claim 1, a method for operating such a power supply system according to patent claim 8 and a power supply for use in such a power supply system or method according to patent claim 13. Advantageous embodiments are the subject matter of the dependent claims.

[0015] A power supply system according to the invention comprises a first power supply and at least one second power supply, which are connected together on the output side in a parallel circuit in order to jointly feed a load, wherein the first power supply is designed to provide a first regulated output voltage and a first output current on the output side, wherein the second power supply is designed to provide a second regulated output voltage and a second output current on the output side. The power supply system is designed to regulate the first output voltage to a predetermined or predeterminable value independently of the first output current, and to regulate the second output voltage in such a way that a difference between the first output current and the second output current is at least reduced, preferably reduced to zero.

[0016] The invention therefore provides for regulating the first output voltage to a predetermined or predeterminable value (e.g. a nominal voltage of the power supply) independently of the first output current and for reducing any differences between the output currents, preferably to zero, by means of the second output voltage. The output currents are thus adjusted to one another by regulating the second output voltage, preferably to the same size. In other words, a difference between the first output current and the second output current is regulated out with the aid of the second output voltage. The output currents can be fed to a controller which then changes the setpoint of the second output voltages in small steps so that any difference between the output currents is reduced, preferably to zero.

[0017] As it turns out, this allows very good balancing of the load currents and ensures that the specified or specifiable (constant) supply voltage is always provided for a load. This also makes it possible to compensate for uneven voltage drops due to poorly laid cables, which lead to uneven load distribution. It is also possible to compensate for uneven load distributions caused by unequal no-load voltages of the power supplies connected in parallel. Due to the good balancing of the output currents, equal utilization, equal aging behavior and thus easier handling of the power supplies for the user can be achieved.

[0018] The load can be a single load. However, it can also consist of several subloads, which are connected to the power system in parallel, for example, via a power bus.

[0019] The control of the second output voltage can be carried out by a central or higher-level control unit, but preferably the control is carried out decentrally by a control unit within the second power supply itself.

[0020] According to a particularly advantageous embodiment,

[0021] - the first power supply is arranged to regulate the first output voltage to the predetermined or predeterminable value independently of the first output current, and

[0022] - the second power supply is arranged to regulate the second output voltage such that the difference between the first output current and the second output current is at least reduced, preferably reduced to zero.

[0023] The first power supply can thus be regarded as the "primary" or "leading" power supply and the at least one second power supply can be regarded as the "secondary" or "following" power supply.

[0024] According to a further particularly advantageous embodiment, the first power supply is designed to detect a value for the first output current and to provide it to the at least one second power supply.

[0025] This can be achieved particularly easily by providing the value in the form of a pulse-width modulated signal (i.e. a PWM signal) whose duty cycle contains information about the value of the first output current. The duty cycle specifies the ratio of the pulse duration to the period duration for a periodic sequence of pulses. For example, a small duty cycle can signal a small output current and a large duty cycle a large output current. Such a signal can be fed from the first power supply to an output terminal, for example, and made available to the second power supply at an input terminal via a simple wire connection. The second power supply can then be set up to determine the first output current from the duty cycle and then compare this with its own output current.The pulse width modulated signal is used to transmit information about the value of the first output current and to derive setpoints for controlling the second power supply, but not for directly intervening in the switching on / off times of switching elements of the second power supply.

[0026] The value of the first output current or the duty cycle of the pulse-width modulated signal is preferably related to a nominal current of the first power supply. Thus, for example, a power supply with a nominal current of 20 A at an output current of 20 A and a power supply with a nominal current of 40 A at an output current of 40 A provide the same duty cycle. If a value of the duty cycle of the pulse-width modulated signal is related to the nominal current rather than the absolute current, power supplies with different output power can also be connected in parallel, for example a power supply with a nominal current of 20 A and a power supply with a nominal current of 40 A. Both power supplies then supply their respective nominal current at the “nominal duty cycle”.Furthermore, it is possible to change the characteristic of the duty cycle, so that, for example, the second power supply delivers a different current than its nominal current at "nominal duty cycle". This allows the load and aging behavior of the power supplies to be specifically adjusted.

[0027] The first power supply and the at least one second power supply are preferably designed as an electronic switching power supply and preferably provide a regulated DC voltage of 24 V or 48 V on the output side.

[0028] Furthermore, the first power supply and the at least one second power supply are preferably each designed as an independent device with its own housing.

[0029] A method according to the invention for operating a power supply system comprises a first power supply and at least one second power supply, which jointly feed a load on the output side in a parallel circuit, wherein the first power supply provides a first regulated output voltage and a first output current on the output side, and wherein the second power supply provides a second regulated output voltage and a second output current on the output side. The first output voltage is regulated to a predetermined or predeterminable value independently of the first output current, and the second output voltage is regulated such that a difference between the first output current and the second output current is at least reduced, preferably reduced to zero.

[0030] An advantageous embodiment of the method provides that

[0031] - the first power supply regulates the first output voltage to the specified or presettable value independently of the first output current,

[0032] - the second power supply regulates the second output voltage such that the difference between the first output current and the second output current is at least reduced, preferably reduced to zero.

[0033] According to a further advantageous embodiment, the first power supply detects a value for the first output current and makes this available to the second power supply.

[0034] The value is preferably provided in the form of a pulse-width modulated signal whose duty cycle contains information about the value of the first output current.

[0035] The value of the first output current or the duty cycle of the pulse-width-modulated signal is advantageously related to a nominal current of the first power supply. The first power supply and the at least one second power supply are preferably designed as an electronic switching power supply and preferably provide a regulated DC voltage of 24 V or 48 V on the output side.

[0036] Furthermore, the first power supply and the at least one second power supply are preferably each designed as an independent device with its own housing.

[0037] A power supply according to the invention for use in a power supply system or method as explained above is designed to provide a regulated output voltage and an output current for feeding a load. It has an interface for providing a value of the output current and for detecting a value of an output current of another power supply. Furthermore, it is designed to provide a first operating mode and a second operating mode, wherein it

[0038] - in the first operating mode, the output voltage is regulated to a predetermined or predeterminable value independently of the output current and the value of the output current is provided at the interface,

[0039] - in the second operating mode, the value of the output current of the other power supply is detected at the interface and the output voltage is regulated in such a way that a difference between the value of the output current and the detected value of the output current of the other power supply is at least reduced, preferably reduced to zero.

[0040] According to an advantageous embodiment, the first operating mode or the second operating mode for the operation of the power supply can be selectively set via the interface. For example, the power supply can be configured to monitor the interface for the presence of a signal containing information about an output current value of another power supply. If such a signal is present, the power supply automatically switches itself to the second operating mode. If no such signal is present, the power supply automatically switches itself to the first operating mode.

[0041] The provision of the value of the output current and the detection of the value of the output current of the other power supply at the interface are each preferably carried out in the form of a pulse-width modulated signal whose duty cycle contains information about the value of the output current.

[0042] According to a further advantageous embodiment, the value of the output current or the duty cycle of the pulse width modulated signal is related to a nominal current of the respective power supply.

[0043] The effects and advantages mentioned for the power supply system according to the invention and its advantageous embodiments apply accordingly to the method according to the invention and the power supply according to the invention and its or their corresponding advantageous embodiments.

[0044] The invention and further advantageous embodiments of the invention according to the features of the dependent claims are explained in more detail below with reference to an exemplary embodiment in the figures. They show:

[0045] FIG 1 shows a first embodiment of a power supply system according to the invention,

[0046] FIG 2 shows a second embodiment of a power supply system according to the invention,

[0047] FIG 3 shows an embodiment of a power supply according to the invention.

[0048] A power supply system 10 according to the invention, shown in FIG. 1 in a simplified, basic representation, comprises two power supplies 1, 2, each designed as a clocked power supply or as a switched-mode power supply (switching power supply). They each have a housing 4 and are designed to be mounted on a top-hat rail. They can thus be installed particularly easily in control cabinets.

[0049] As a rule, a switch-mode power supply comprises a power section and a control and / or regulating unit (hereinafter referred to as "controller") for controlling the power section. The power section essentially consists of a converter, with different types such as flyback converters, forward converters, push-pull converters, boost converters, buck converters, etc. being known. Depending on the current form occurring on the input and output sides, a further distinction is made between, for example, direct current-to-direct current converters (DCDC converters), alternating current-to-direct current converters (AC-DC converters) or direct current-to-alternating current converters (DC-AC converters).

[0050] In the exemplary embodiment according to FIG 1, it is assumed that a DC voltage load 3 is to be supplied from a supply network 11 in the form of an AC voltage network and thus an AC-DC converter W is used.

[0051] The power supplies 1, 2 are therefore supplied on the input side in a single-phase manner from the supply network 11 with an input voltage Ue, which is formed, for example, by a voltage difference between an outer conductor L and the neutral conductor N of the supply network 11. In principle, however, a three-phase supply from a supply network is also possible.

[0052] The AC-DC converter W comprises, for example, a rectifier unit G, an intermediate circuit Z and a switching converter S .

[0053] The input voltage Ue, which can be a 230V AC voltage, for example, is converted via the rectifier unit G as the input stage into a rectified intermediate circuit voltage UZ on an output side of the rectifier unit G or on an input side of the intermediate circuit Z. The intermediate circuit Z can, for example, comprise an intermediate circuit capacitor C. Further components can also be connected in the intermediate circuit Z, e.g. further capacitors to improve the EMC properties.

[0054] The switching converter S is arranged on an output side of the intermediate circuit Z and has at least one periodically operating electronic switching element. It can be designed, for example, as a potential-isolating switching converter with galvanic isolation (e.g., a transformer) or as a potential-bound (i.e., non-potential-isolating) switching converter S without galvanic isolation.

[0055] By regulating the energy flow through the converter W with the aid of a controller Kl or K2, the mostly unstabilized input voltage Ue is converted into a regulated output voltage Ul or U2 (e.g. a direct voltage of 24 V or 48 V) to supply the load 3.

[0056] The two power supplies 1, 2 are connected in parallel on the output side to jointly feed load 3. Load 3 can be a single load. However, the load can also consist of several partial loads, which are connected to the power supply system 10 in parallel, for example, via a power bus.

[0057] The power supply 1 or its controller K1 is configured to measure the output voltage U1 and the output current II using a measuring device (not shown in detail). It is also configured to measure the voltage Ue of the supply network 11 and a current drawn from the supply network (not shown).

[0058] According to the invention, the power supply 1 or its controller Kl is designed to regulate the output voltage Ul independently of the output current II to a predetermined or predeterminable value, e.g. to a nominal voltage Un of the power supply 1 or of the DC voltage supply network 5 for the load 3.

[0059] In contrast, the power supply 2 or its controller K2 is configured to regulate the output voltage U2 such that a difference between the output current II of the power supply 1 and the output current I2 of the power supply 2 is at least reduced, preferably to zero. For this purpose, the controller K2 may comprise a control unit (not shown in detail).

[0060] The power supply 1 or the controller K1 thus always regulates the output voltage U1 to the nominal voltage Un, regardless of the output current II. The power supply 2 or the controller K2, on the other hand, regulates the output voltage U2 by making small, step-by-step changes such that any differences between the output currents II and II are reduced, preferably to zero.

[0061] This allows a very good symmetrization of the output currents II and I2 to be achieved and ensures that the nominal voltage Un is always provided for the load 3.

[0062] Power supply 1 can be considered as the "primary" or "leading" power supply and power supply 2 can be considered as the "secondary" or "following" power supply.

[0063] The power supply 1 or its controller Kl is designed to record a value for the output current II by means of a measuring device not shown in detail and to make this value available to the power supply 2 via an interface 6.

[0064] The value is preferably provided in the form of a pulse-width modulated signal (i.e., a PWM signal) whose duty cycle contains information about the value of the output current II. For example, a small duty cycle can signal a small output current, and a large duty cycle can signal a large output current.

[0065] This signal is routed to an output terminal of interface 6 .

[0066] The power supply 2 or its controller K2 is designed to detect the value for the output current II provided by the power supply 1 via an interface 8.

[0067] For this purpose, the output terminal of the interface 6 of the power supply 1 is connected to an input terminal of the interface 8 of the power supply 2 via a simple wire connection 7.

[0068] The power supply 2 or its controller K2 is designed to determine the value of the output current II from the duty cycle of the pulse-width modulated signal detected at the input terminal of the interface 8 and to compare this with the output current I2 in order to then reduce the difference between the first output current II and the second output current I2 by regulating the second output voltage U2, preferably to reduce it to zero.

[0069] The value of the output current II or the duty cycle of the pulse-width-modulated signal is related to a nominal current of the power supply 1. Thus, for example, the power supply 1 generates the same duty cycle with an output current of 20 A in the case of a nominal current of 20 A and with an output current of 40 A in the case of a nominal current of 40 A.

[0070] If the duty cycle of the pulse-width-modulated signal is not related to the absolute current but to the rated current, power supplies with different output power can also be connected in parallel, for example, power supply 1 with a rated current of 40A and power supply 2 with a rated current of 20A. Both power supplies then deliver their respective rated current on the output side at the "rated duty cycle".

[0071] It is also possible to change the characteristic of the duty cycle so that, for example, power supply 2 delivers a different current than its rated current at "rated duty cycle". This allows the load and aging behavior of power supplies 1, 2 to be specifically adjusted.

[0072] During operation of the power supply system 10, the output voltage Ul is thus regulated to the nominal voltage Un by the controller K1 of the power supply 1, independently of the output current II. The output voltage U2, on the other hand, is regulated by the controller K2 of the power supply 2 in such a way that a difference between the output current II and the output current I2 is at least reduced, preferably to zero.

[0073] In a power supply system 20 according to the invention shown in FIG. 2, two power supplies 21, 22, in contrast to FIG. 1, have a common controller K which is set up to regulate the output voltage Ul of the power supply 21, independently of its output current II, to a predetermined or predeterminable value, here for example the nominal voltage Un of the power supply 21 or of the supply network 5, and to regulate the output voltage U2 of the power supply 2 in such a way that a difference between the output current II and the output current I2 is at least reduced, preferably reduced to zero. Functionally identical components as in FIG. 1 are provided with the same reference numerals. The effects and advantages mentioned in connection with FIG. 1 can also be achieved accordingly in this embodiment.

[0074] During operation of the power supply system 20, the output voltage Ul is thus regulated by the central controller K to the nominal voltage Un independently of the output current II. The output voltage U2, on the other hand, is regulated by the controller K in such a way that a difference between the output current II and the output current I2 is at least reduced, preferably to zero.

[0075] In the embodiments according to FIGS. 1 and 2, only one "secondary" or "following" power supply is present. However, it is also possible in principle for several "secondary" or "following" power supplies with the same properties as power supply 2 or 22 to be present and connected in parallel to the "primary" or "leading" power supply with the same properties as power supply 1 or 21.

[0076] A power supply 30 according to the invention shown in FIG. 3 can be used for the power supplies 1, 2 in the power supply system 10 shown in FIG. 1. It comprises the functionalities of both power supplies 1, 2 explained in FIG. 1. Components that are functionally identical to those in FIG. 1 are provided with the same reference numerals.

[0077] The power supply 30 is designed to provide a regulated output voltage U and an output current I on the output side for feeding a load. It comprises a controller K' for controlling a converter W (as explained in connection with the controllers K1, K2 of FIG. 1). Furthermore, it has an interface 31, which in turn comprises an output terminal 32 for providing a value of the output current I and an input terminal 33 for detecting a value of an output current of another power supply.

[0078] The controller K' is set up to provide a first operating mode in which it regulates the output voltage U to a predetermined or predeterminable value, here for example the nominal voltage Un of the power supply or a supply network connected to it, independently of the output current I, and provides the value of the output current I at the output terminal 32 of the interface 31. The controller K' is also set up to provide a second operating mode in which it detects the value of the output current of the other power supply at the input terminal 33 of the interface 31 and regulates the output voltage U such that a difference between the value of the output current I and the detected value of the output current of the other power supply is at least reduced, preferably reduced to zero.

[0079] The controller K ' is designed to provide the value of the output current I at the output terminal 32 of the interface 31 in the form of a pulse-width modulated signal (PWM), the duty cycle of which contains information about the value of the output current I .

[0080] Conversely, the controller K ' is also designed to detect, via the input terminal 33 of the interface 31, a value of the output current of another power supply, which is provided or is present at the input terminal 33 in the form of a pulse-width modulated signal (PWM), and whose duty cycle contains information about the value of the output current of the other power supply.

[0081] The value of the output current or the duty cycle of the pulse width modulated signal (PWM) is advantageously related to a nominal current of the power supply that provides the value or the signal (PWM).

[0082] Via the interface 31 or its terminals 32, 33 it can be set whether the power supply 30 is to be operated in the first operating mode or in the second operating mode. For this purpose the controller K' is set up to monitor the input terminal 33 for a pulse width modulated signal which is provided there or present from another power supply and whose duty cycle contains information about a value of an output current from another power supply. If such a signal is present, the controller K' or the power supply 30 automatically switches itself to the second operating mode. If no such signal is present, the controller K' or the power supply 30 automatically switches itself to the first operating mode. The controller K' can therefore recognize on its own in which operating mode it or the power supply 30 should be operated.

[0083] Alternatively, the power supply 30 can also have an interface with just a single terminal, which serves both to provide a value of the (own) output current I and to detect a value of an output current of another power supply. In addition, the power supply 30 can then have a further interface (not shown in detail) via which the operating mode (here the first operating mode or the second operating mode) for the operation of the power supply 30 can be set. This interface can, for example, comprise a mechanical switch, the switching state of which can be read out by the controller K'. However, it can also be, for example, an operating and display unit of the power supply or a communication interface to a configuration device or a higher-level configuration software.

[0084] The effects and advantages mentioned in connection with FIG 1 can therefore also be achieved with the power supply 30.

Claims

Patent claims 1. A power supply system (10) comprising a first power supply (1) and at least one second power supply (2), which are connected together on the output side in a parallel circuit to jointly feed a load (3), wherein the first power supply (1) is configured to provide a first regulated output voltage (U1) and a first output current (U1) on the output side, wherein the second power supply (2) is configured to provide a second regulated output voltage (U2) and a second output current (U2) on the output side, characterized in that the power supply system (10) is configured to regulate the first output voltage (U1) to a predetermined or predeterminable value independently of the first output current (U1) and to regulate the second output voltage (U2) such that a difference between the first output current (U1) and the second output current (U2) is at least reduced, preferably reduced to zero.

2. Power supply system (10) according to claim 1, wherein - the first power supply (1) is designed to regulate the first output voltage (Ul) to the predetermined or predeterminable value independently of the first output current (II), and - the second power supply (2) is designed to regulate the second output voltage (U2) such that the difference between the first output current (II) and the second output current (I2) is at least reduced, preferably reduced to zero.

3. Power supply system (10) according to claim 2, wherein the first power supply (1) is configured to detect a value for the first output current (II) and to provide it to the at least one second power supply (2).

4. Power supply system (10) according to claim 3, wherein the value is provided in the form of a pulse width modulated signal (PWM) whose duty cycle contains information about the value of the first output current (II).

5. Power supply system (10) according to claim 3 or 4, wherein the value of the first output current (II) or the duty cycle of the pulse width modulated signal (PWM) is related to a rated current of the first power supply (1).

6. Power supply system (10) according to one of the preceding claims, wherein the first power supply (1) and the at least one second power supply (2) are each designed as an electronic switching power supply.

7. Power supply system (10) according to one of the preceding claims, wherein the first power supply (1) and the at least one second power supply (2) are each designed as an independent device with its own housing (4).

8. Method for operating a power supply system (10) comprising a first power supply (1) and at least one second power supply (2), which on the output side feed a load (3) in a parallel circuit, wherein the first power supply (1) provides a first regulated output voltage (U1) and a first output current (II) on the output side, wherein the second power supply (2) provides a second regulated output voltage (U2) and a second output current (U2) on the output side, characterized in that the first output voltage (U1) is regulated to a predetermined or predeterminable value independently of the first output current (II), and the second output voltage (U2) is regulated such that a difference between the first output current (II) and the second output current (U2) is at least reduced, preferably reduced to zero.

9. The method according to claim 8, wherein - the first power supply (1) regulates the first output voltage (Ul) to the specified or predeterminable value independently of the first output current (II), - the second power supply (2) regulates the second output voltage (U2) such that the difference between the first Output current (II) and the second output current (12) is at least reduced, preferably reduced to zero.

10. The method according to claim 9, wherein the first power supply (1) detects a value for the first output current (II) and provides it to the second power supply (2).

11. The method according to claim 10, wherein the value is provided in the form of a pulse width modulated signal (PWM) whose duty cycle contains information about the value of the first output current (II).

12. The method according to claim 10 or 11, wherein the value of the first output current (II) or the duty cycle of the pulse width modulated signal (PWM) is related to a nominal current of the first power supply (1).

13. Power supply (30) for use in a power supply system (10) according to claim 1 or a method according to claim 8, which is designed to provide a regulated output voltage (U) and an output current (I) on the output side for feeding a load (3), characterized in that the power supply (30) has an interface (31) for providing a value of the output current (I) and for detecting a value of an output current of another power supply, and that it is designed to provide a first operating mode and a second operating mode, wherein it - in the first operating mode, the output voltage (U) is set to a predetermined or predeterminable value and provides the value of the output current (I) at the interface (31), - in the second operating mode, the value of the output current (I) of the other power supply is detected at the interface (31) and the output voltage (U) is regulated in such a way that a difference between the value of the output current (I) and the value of the output current of the other power supply is at least reduced, preferably reduced to zero.

14. Power supply (30) according to claim 13, wherein the first operating mode or the second operating mode for the operation of the power supply (30) can be selectively set via the interface (31).

15. Power supply (30) according to claim 13 or 14, wherein the provision of the value of the output current (I) and the detection of the value of the output current of the other power supply at the interface (31) each take place in the form of a pulse width modulated signal (PWM) whose duty cycle contains information about the value of the output current.

16. Power supply (30) according to one of claims 13 to 15, wherein the value of the output current (I) or the duty cycle of the pulse width modulated signal (PWM) is related to a nominal current of the power supply (30) which provides the value or the signal (PWM).

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