DE102020003802A1 - Method and system with a DC voltage intermediate circuit supported by a DC / DC converter from an energy store and a power supply unit - Google Patents

Abstract

where a temporally constant electrical power P is continuously supplied to the resistor R to discharge the energy store, in particular during a period of time T, in particular until the resistor is almost completely discharged, in particular where the period of time T is greater than the time constant of the one applied to the resistor The continuous electrical power supplied, which is constant over time, causes the temperature of the resistance R to rise.

Description

The invention relates to a method and a system with a DC voltage intermediate circuit supported by a DC / DC converter from an energy store and a power supply unit.

It is well known that braking resistors are used to reduce the energy generated by electric motors in generator mode, so that dangerously high voltages are prevented.

The invention is therefore based on the object of making a system as safe as possible.

According to the invention, the object is achieved in the method according to the features specified in claim 1 or 2 and in the system according to the features specified in claim 12.

• - der DC/DC-Wandler an seinem ersten Anschluss in einem ersten Betriebszustand, insbesondere und bei betriebsbereitem Wechselspannungsversorgungsnetz, eine erste Spannung bereitstellt,
• - wobei der DC/DC-Wandler an seinem ersten Anschluss in einem zweiten Betriebszustand, insbesondere und bei erkanntem Netzausfall, also Ausfall des Wechselspannungsversorgungsnetzes, eine zweite Spannung bereitstellt,

wobei die erste Spannung größer als eine Mindestspannung ist,
wobei die zweite Spannung kleiner als die die Mindestspannung ist,
insbesondere wobei ein aus dem ersten Anschluss des DC/DC-Wandler versorgter Wechselrichter abgeschaltet wird, wenn die an diesem ersten Anschluss anliegende Spannung kleiner als die Mindestspannung ist.Important features of the invention in the method according to claim 1 for operating the system are that the system with a DC voltage intermediate circuit supported by a DC / DC converter from an energy store and a power supply unit which can be supplied from an AC voltage supply network and from the intermediate circuit and which provides a low voltage, in particular 24 volts, is provided, wherein the DC / DC converter is operated in such a way that

• - The DC / DC converter provides a first voltage at its first connection in a first operating state, in particular and when the AC voltage supply network is ready for operation,
• - wherein the DC / DC converter provides a second voltage at its first connection in a second operating state, in particular and when a power failure is detected, i.e. failure of the AC voltage supply network,

where the first voltage is greater than a minimum voltage,
where the second voltage is smaller than the minimum voltage,
in particular wherein an inverter supplied from the first connection of the DC / DC converter is switched off when the voltage applied to this first connection is less than the minimum voltage.

The advantage here is that the power supply unit still provides the low voltage for as long as possible after the power failure and thus the signal electronics areas of the modules supplied by the power supply unit can be kept ready for operation. This increases security, since the monitoring and security functions carried out by the respective signal electronics areas are ready for operation for as long as possible.

Important features of the invention in the method according to claim 2 are that the system is designed with a supply module, an inverter, a DC / DC converter, an energy store and a power supply unit,
wherein the DC voltage side connection of the supply module having a rectifier is electrically connected in parallel to the DC voltage side connection of the inverter and to the first connection of the DC / DC converter, to whose second connection the energy store is connected,
wherein the AC voltage side connection of the rectifier is fed from an AC voltage supply network,
wherein a low voltage, in particular 24 volts, is fed to the supply module, the DC / DC converter and the inverter from a first DC-side connection of the power supply unit,
an AC voltage-side connection of the power supply unit is fed from the AC voltage supply network,
wherein a second DC voltage-side connection of the power supply unit is connected in parallel to the DC voltage-side connection of the supply module,
wherein in a first operating state, in particular and when the AC voltage supply network is ready for operation, the DC / DC converter provides a first voltage at its first connection,
wherein in a second operating state, in particular and when a network failure is detected, i.e. failure of the AC voltage supply network, the DC / DC converter provides a second voltage at its first connection,
wherein the first voltage is greater than a minimum voltage, in particular 400 volts, wherein the second voltage is less than the minimum voltage,
wherein the inverter is switched off when the voltage applied to its DC voltage-side connection is less than the minimum voltage.

The advantage here is that the power supply unit still provides the low voltage for as long as possible after the power failure and thus the signal electronics areas of the modules supplied by the power supply unit can be kept ready for operation. This increases safety, since the monitoring and safety functions carried out by the respective signal electronics areas are ready for operation for as long as possible.

In an advantageous embodiment, sensors for network failure detection are arranged in the supply module. The advantage here is that the information about the power failure can be recognized directly on the AC voltage supply network and means data bus connection to the bus subscribers connected for data exchange can be reported, in particular also to the DC / DC converter, which then sets the operating state depending on the information. It is therefore important that the measurement technology for detecting the power failure is located in a different device than in the DC / DC converter. This measurement technology is otherwise required for the function and mode of operation of the supply module, since it has a DC / DC converter arranged on the DC / DC connection of the rectifier of the supply module, so that the power flow from the rectifier into the intermediate circuit can be controlled.

In an advantageous embodiment, to discharge the energy store, a resistor R, in particular a braking resistor, is supplied with an electrical power P which is constant over time, in particular during a period of time T, in particular until the resistor is practically completely discharged,
in particular wherein the time period T is greater than the time constant of the temperature rise of the resistor R caused by a constant electrical power supplied to the resistor.

The advantage here is that power is not only applied to the resistor for a short time in order to lower the intermediate circuit voltage, but that the greatest possible power P is applied permanently. This power is preferably so great that the resistor is just not destroyed. Thus, the maximum permissible power can be permanently dissipated to the environment as heat. By means of this method according to the invention, the smallest possible resistance value can be used, that is to say rapid discharge of the energy store can be carried out. Such discharges are important in the case of transport and service.

In an advantageous embodiment, the voltage U present at a series circuit formed from the resistor and a controllable semiconductor switch, in particular a brake chopper, is detected,
The series connection is either fed directly from the voltage made available by the energy store or is fed from the voltage made available by the energy store via a DC / DC converter,
wherein the controllable semiconductor switch is supplied with a pulse-width-modulated control signal with a pulse-width modulation ratio that is dependent on the value of the detected voltage,
in particular where the pulse width modulation ratio is determined according to (1 / U) * (P * R) ^ ½. The advantage here is that the pulse width modulation ratio is changed as a function of the voltage, in particular is increased when the voltage drops.

In an advantageous embodiment, the controllable half-liter switch is permanently closed when the voltage U falls below a threshold value, in particular where the threshold value is (P * R) ^ ½. This enables particularly fast deep discharge when the maximum power that can be fed to the resistor is in the permissible range. Pulse width modulation is then avoided.

In an advantageous embodiment, the system has a supply module comprising a mains-fed rectifier, the DC voltage side of which is connected to the DC voltage side connection of an inverter and to the first connection of a DC / DC converter,
wherein the second connection of the DC / DC converter is connected to the connection of the energy store providing the voltage U,
wherein an electric motor, in particular a three-phase motor, is connected to the connection on the AC voltage side of the inverter. The advantage here is that the system has an energy storage device which buffers the energy generated by the electric motor as a generator and thus keeps the power consumption from the AC voltage supply network small when motor power is drawn from the intermediate circuit.

In an advantageous embodiment, a DC / DC converter is arranged between the DC voltage side connection of the rectifier and the DC voltage side connection of the supply module,
which stops the power flow from the rectifier to the series circuit formed by the resistor R and the controllable half-liter switch while the energy store is being discharged,
in particular so that on the power module on which the diodes of the rectifier and the controllable half-liter switch are integrated, heat is generated during discharging by either the controllable semiconductor switch or alternatively by the diodes of the rectifier. The advantage here is that the power flow from the AC voltage supply network to the intermediate circuit can be interrupted. This is particularly important when unloading.

In an advantageous embodiment, the inverter has a power module on which controllable semiconductor switches arranged in half bridges are arranged. The advantage here is that the controllable half-liter switches can be designed as circuit breakers and still be structurally integrated, that is, can be arranged on a common carrier.

In an advantageous embodiment, the power P is less than the maximum power that can be fed back from the electric motor via the inverter to the DC voltage-side connection of the inverter in the generator operation of the electric motor. The advantage here is that a permanently constant power can be dissipated by means of the energy store, but the excess energy in the generator operating mode must be stored in the energy store.

In an advantageous embodiment, the pulse width modulation frequency of the control signal is changed while the power P is being supplied, in particular during the time period T,
in particular, different, in particular discrete values can be used as the pulse width modulation frequency in chronological succession. The advantage here is that the noise emission can be reduced or at least no monofrequency tone can be heard, but the sound energy can be divided into different frequencies. The sound impression is therefore more acceptable.

In an advantageous embodiment, the current I flowing through the resistor R is detected,
The current resistance value of the braking resistor is determined from the time-averaged voltage provided via the brake chopper and the time-averaged current, in particular according to U / I,
and taking into account a characteristic that represents the temperature dependency of the braking resistor, the current temperature T of the respective braking resistor is determined. The advantage here is that the temperature can be determined from the specific voltage and the specific current.

In an advantageous embodiment, it is monitored whether the specific temperature T of the braking resistor exceeds a threshold value, in particular wherein an emergency shutdown of the brake chopper is carried out when it is exceeded. The advantage here is that destruction of the braking resistor can be avoided.

In an advantageous embodiment, the specific temperature is regulated to a setpoint temperature in that the power P is set accordingly as a control value of a controller, in particular a PI controller. The advantage here is that maximum power can be dissipated from the energy store to the environment even when the ambient temperature changes.

• - der DC/DC-Wandler in einem ersten Betriebszustand, insbesondere und bei betriebsbereitem Wechselspannungsversorgungsnetz, an seinem ersten Anschluss eine erste Spannung bereitstellt, und
• - der DC/DC-Wandler in einem zweiten Betriebszustand, insbesondere und bei erkanntem Netzausfall, also Ausfall des Wechselspannungsversorgungsnetzes, an seinem ersten Anschluss eine zweite Spannung bereitstellt,

wobei die erste Spannung größer als eine Mindestspannung, insbesondere 400 Volt, ist, wobei die zweite Spannung kleiner als die eine Mindestspannung ist,
insbesondere wobei der Wechselrichter derart geeignet ausgeführt ist, dass der Wechselrichter abgeschaltet wird, wenn die an seinem gleichspannungsseitigen Anschluss anliegende Spannung kleiner als die Mindestspannung ist.Important features of the system, in particular for carrying out the aforementioned method, are that
the system is designed with a supply module, an inverter, a DC / DC converter, an energy store and a power supply unit,
wherein the DC voltage side connection of the supply module having a rectifier is electrically connected in parallel to the DC voltage side connection of the inverter and to the first connection of the DC / DC converter, to whose second connection the energy store is connected,
wherein the AC voltage side connection of the rectifier is fed from an AC voltage supply network,
wherein a low voltage, in particular 24 volts, is fed to the supply module, the DC / DC converter and the inverter from a first DC-side connection of the power supply unit,
an AC voltage-side connection of the power supply unit is fed from the AC voltage supply network,
wherein a second DC voltage-side connection of the power supply is connected in parallel to the DC-side connection of the supply module, in particular so that the power supply can be supplied from the AC voltage supply network and / or via the DC / DC converter from the energy store,
wherein the DC / DC converter is designed so that

• the DC / DC converter provides a first voltage at its first connection in a first operating state, in particular and when the AC voltage supply network is ready for operation, and
• - the DC / DC converter provides a second voltage at its first connection in a second operating state, in particular and when a power failure is detected, i.e. failure of the AC voltage supply network,

wherein the first voltage is greater than a minimum voltage, in particular 400 volts, wherein the second voltage is less than the minimum voltage,
in particular, the inverter being designed in such a way that the inverter is switched off when the voltage applied to its terminal on the DC voltage side is less than the minimum voltage.

The advantage here is that the power supply unit still provides the low voltage for as long as possible after the power failure and thus the signal electronics areas of the modules supplied by the power supply unit can be kept ready for operation.

In an advantageous embodiment, sensors for power failure detection are arranged in the supply module. The advantage here is that the information about the power failure can be recognized directly on the AC voltage supply network and via a data bus connection to the data exchange connected bus subscribers can be reported, in particular to the DC / DC converter, which then adjusts the operating state depending on the information. It is therefore important that the measurement technology for detecting the power failure is located in a different device than in the DC / DC converter. This measurement technology is otherwise required for the function and mode of operation of the supply module, since it has a DC / DC converter arranged on the DC / DC connection of the rectifier of the supply module, so that the power flow from the rectifier into the intermediate circuit can be controlled.

In an advantageous embodiment, the system has a supply module comprising a mains-fed rectifier, the DC voltage side connection of which is connected to the DC voltage side connection of an inverter of the system and to the first DC voltage side connection of a DC / DC converter of the system,
wherein the second DC voltage-side connection of the DC / DC converter is connected to the energy store, in particular a battery arrangement and / or double-layer capacitor arrangement and / or ultracap arrangement,
wherein an electric motor, in particular a three-phase motor, is connected to the connection on the AC voltage side of the inverter. The advantage here is that the energy store can be discharged for transport purposes or maintenance purposes. This discharging can be carried out quickly because a very low ohmic resistance value can be used. This is because by detecting the voltage applied to the series circuit, a constant power can be dissipated to the resistor by means of an appropriately suitable pulse width modulation, and rapid discharge can also be carried out at low voltages.

In an advantageous embodiment, a DC / DC converter is arranged between the DC voltage side connection of the rectifier and the DC voltage side connection of the supply module. The advantage here is that the power flow from the rectifier to the intermediate circuit can be influenced, in particular switched off. In addition, the voltage level present at the DC voltage side connection of the rectifier is different from the intermediate circuit level, that is to say from the level of the voltage at the DC voltage side connection of the inverter or of the supply module.

In an advantageous embodiment, a controllable semiconductor switch connected in series with the braking resistor is arranged in the housing of the DC / DC converter. The advantage here is that the controllable semiconductor switch can be designed to be integrated with the other electronics of the DC / DC converter and can then also be heat-dissipated with this.

In an advantageous embodiment, a controllable semiconductor switch connected in series with the braking resistor is integrated on a power module which has diodes and / or controllable semiconductor switches arranged in half bridges. The advantage here is that the rectifier is integrated with the controllable semiconductor switch and is designed to be heatable together. However, since the power flow from the rectifier to the intermediate circuit is stopped, in particular separated, by the converter when the energy store is discharged by means of the resistor, in particular the braking resistor, the power losses of the diodes of the rectifier and the power loss of the controllable semiconductor switch occur only alternatively.

In an advantageous embodiment, the power module is arranged in the housing of the inverter or of the supply module. The advantage here is that the controllable semiconductor switch can be arranged integrated in the power module and thus the heat dissipation of the controllable power module can be carried out with the heat dissipation of the power module, in particular by means of a heat sink, which absorbs the heat loss of the controllable semiconductor switches of the inverter arranged in half bridges and that assigned to the resistor , controllable semiconductor switch dissipates to the environment.

Further advantages result from the subclaims. The invention is not restricted to the combination of features of the claims. For the person skilled in the art, there are further meaningful possible combinations of claims and / or individual claim features and / or features of the description and / or the figures, in particular from the task and / or the task posed by comparison with the prior art.

• In der 1 ist ein erfindungsgemäßes System schematisch dargestellt.

The invention will now be explained in more detail with reference to schematic figures:

• In the 1 a system according to the invention is shown schematically.

As shown in the figure, one represents an AC voltage supply network 8th powered supply module 1 a unipolar voltage is available at its connection on the DC voltage side.

The DC voltage side of an inverter is connected to this connection 2 connected to the AC voltage side connection of the inverter 2 from the inverter 2 a three-phase voltage to an electric motor 4th , in particular AC motor, in particular three-phase motor, is made available.

The inverter is controlled by control electronics 3 controlled. In particular, the control electronics generate 3 pulse-width-modulated control signals for the controllable semiconductor switches of the inverter, which are arranged in half bridges connected in parallel to one another, this parallel connection of half bridges being able to be fed from the unipolar voltage.

Structurally, these semiconductor switches, in particular six controllable semiconductor switches, are integrated on a module on which a further controllable semiconductor switch is also integrated, which can be referred to as a brake chopper.

The brake chopper is equipped with a resistor that acts as a braking resistor ( 7th , 12 ) can be designated, connected in series, this series connection also being able to be fed from the unipolar voltage.

At the DC voltage-side connection of the supply module 1 is also a connection for a DC / DC converter 5 connected so this DC / DC converter 5 parallel to the inverter 2 is switched.

At the other connection of the DC / DC converter 5 is an energy store 6th connected. Thus the DC / DC converter enables 5 a power flow from the energy storage 6th to the intermediate circuit having the unipolar voltage or vice versa, even if the amount of the unipolar voltage is very different from the amount of the energy store 6th applied voltage.

The energy storage 6th can be implemented as an electrolytic capacitor arrangement, as a double-layer capacitor arrangement and / or preferably as an accumulator arrangement.

The supply module 1 can be implemented as a mains-fed rectifier. Preferably, however, there is between the mains-fed rectifier and the DC voltage-side connection of the supply module 1 a DC / DC converter arranged so that the power flow from the AC voltage supply network 8th can be controlled into the intermediate circuit.

The rectifier in turn preferably has a module on which the diodes of the rectifier are integrated and on which a further controllable semiconductor switch is also integrated, which can be referred to as a brake chopper.

The brake chopper is with another resistor 13th , which can be referred to as a braking resistor, is connected in series, this series connection also being able to be fed from the DC voltage-side connection of the rectifier.

The DC / DC converter 5 also includes a further controllable semiconductor switch is integrated, which can be referred to as a brake chopper.

This brake chopper comes with another resistor 7th , which can be referred to as a braking resistor, connected in series, this series connection also consisting of the DC voltage side connection of the rectifier or the connection to the energy store 6th applied voltage can be fed.

This means that several brake choppers can be provided in the system.

According to the invention, the security of the system is increased in that the energy store can be discharged in a controlled manner.

This is not only when transporting the energy storage device 6th important, but also during maintenance work on the system when the energy storage device is to be discharged. Discharging is also important for special types of energy storage if a memory effect is to be prevented. For example, NiCd batteries are regularly discharged over time.

Discharging takes place in such a way that the brake chopper of the respective braking resistor ( 7th , 12 , 13th ) depending on the unipolar voltage or on the voltage U applied to the series circuit formed by the braking resistor and the associated braking chopper, is controlled in such a way that the respective braking resistor R is continuously supplied with a constant power.

This electrical power P supplied to the respective braking resistor permanently until the energy store is practically completely discharged is specified as high as possible. It is therefore preferably the same as the rated power of the braking resistor R.

For this purpose, the voltage U is recorded and the respective brake chopper is preferably controlled with a pulse width modulation ratio (1 / U) * (P * R) ^ ½. In this way, the power supplied to the respective braking resistor remains constant even when the voltage U drops.

In particular, the nominal power, that is to say also the power P, is smaller than that in the generator operation of the electric motor from the electric motor 4th via the inverter 2 maximum regenerative power.

The ohmic resistance of the respective braking resistor R can thus be selected to be very small and therefore a practically complete discharge can be achieved in a short time.

If the voltage falls below a threshold value, the pulse width modulation can even be replaced by permanently closing the controllable switch. In this way, a particularly fast total discharge is made possible. As soon as the voltage falls below a second, even smaller threshold value, the switch is then opened again in order to protect the battery cells against destruction.

In the way described, energy from the intermediate circuit is therefore available via the braking resistors ( 7th , 12, 13th ) convertible into heat.

If the from the braking resistor 7th and the series circuit formed to it is fed directly from the voltage applied to the energy store, deep discharging of the energy store is made possible in a simple manner because the DC / DC converter 5 cannot work without a minimum voltage and therefore no discharge through the braking resistors below the minimum voltage 12 and 13th is executable. Because those from the respective brake chopper and the brake resistor stand 12 or 13th The series connection formed is only indirect via the DC / DC converter 5 supplied by the energy store.

When the energy store is discharged 6th directs the supply module 1 no electrical power from the AC voltage supply network through to the intermediate circuit.

According to the invention is a power supply 9 that on the one hand from the AC voltage supply network 8th can also be supplied on the other hand from the intermediate circuit, that is to say from a direct voltage. This means that even in the event of a power failure, a supply is still available because it comes from the energy store 6th via the DC / DC converter 5 Energy can still be fed to the intermediate circuit.

Thus is from the power supply 9 A low voltage, in particular 24 volts, can be provided within a period of time after the occurrence of the power failure. However, the time span is limited by the energy that is in the memory 6th is present, and by possibly further power sinks arranged on the intermediate circuit.

With the one from the power supply 9 The low voltage provided can be at least a partial area, signal electronics area, supplied by components of the system, such as part of the signal electronics of the supply module 1 , part of the signal electronics of the DC / DC converter 5 , the signal electronics 3 of the inverter 2 , a higher-level controller 10 as well as other consumers that can be fed by the extra-low voltage.

There is no power failure in normal operation. Then the DC / DC converter continues 5 those on the energy storage 6th voltage provided to the first voltage required in the intermediate circuit, i.e. the nominal intermediate circuit voltage, up or down if necessary. This first voltage is greater than a minimum voltage, in particular 400 volts.

The inverter is below the minimum voltage 2 switched off.

On the mains side are on the supply module 1 Sensors attached, in particular means for detecting the phase voltages of the AC voltage supply network designed as a three-phase network. The signal electronics of the supply module 1 also functions as an evaluation unit for these signals on the network side on the supply module 1 arranged sensors. As soon as a power failure is detected, corresponding information is reported to the other bus users via the data bus, the DC / DC converter 5 designed as a bus user

If a power failure is detected, the DC / DC converter 5 the DC link voltage is still available to the DC link until the inverter 2 is in a safe state, especially that of the inverter 2 powered electric motor 4th is braked.

After receiving the information that the safe state has been reached, the DC / DC converter 5 only a second voltage in the intermediate circuit, which is less than the minimum voltage. For example, the second voltage is slightly more than 24 volts, so that 24 volts can be made available by the power pack.

The DC / DC converter is preferably used by signal electronics 5 from the one from the DC / DC converter 5 The current flowing into the intermediate circuit and the voltage recorded at the intermediate circuit determine the power consumed by the system and from this, taking into account the current data in the memory 6th existing charging energy determines the respective remaining running time, the remaining running time being the time in which the power supply unit is still able to provide the second voltage to the intermediate circuit.

In further exemplary embodiments according to the invention, no DC / DC converter is used 5 provided, but the energy storage 6th connected directly to the intermediate circuit. The voltage is below the minimum, i.e. when the inverter is switched off 2 , the remaining energy of the energy store 6th the power supply 9 Provided as completely as possible, so that the low voltage through the power supply unit 9 can be provided for as long as possible.

In further exemplary embodiments according to the invention, the current flowing through the respective braking resistor is recorded and the current resistance value of the braking resistor is determined from the time-averaged voltage provided via the brake chopper and the recorded and time-averaged current, taking into account a characteristic curve that shows the temperature dependency of the braking resistor represents the current temperature of the respective braking resistor.

Thus, on the one hand, it can be monitored whether the temperature of the braking resistor exceeds a threshold value and whether an emergency shutdown of the brake chopper is necessary. On the other hand, an output adapted to the specific temperature can alternatively be set. This means that the power P follows the temperature. A change in the ambient temperature or a deterioration in the heat transfer resistance acting on the environment from the braking resistor can thus be taken into account.

In further exemplary embodiments according to the invention, a constant pulse width modulation frequency is not used, but the pulse width modulation frequency is changed continuously or in segments. In this way, less disruptive noise emission can be brought about.

List of reference symbols

1

Supply module

2

Inverter

3

Control electronics

4th

Electric motor

5

DC / DC converter

6th

Energy storage

7th

Braking resistor

8th

AC voltage supply network

9

double-sided power supply unit

10

higher-level control

11

Bus participants, especially consumers

12

Braking resistor

Claims (15)

Method for operating a system with a DC voltage intermediate circuit supported by a DC / DC converter from an energy store and a power supply unit which can be supplied from an AC voltage supply network and from the intermediate circuit and which provides a low voltage, in particular 24 volts, characterized in that the DC / DC converter is operated in such a way that the DC / DC converter provides a first voltage at its first connection in a first operating state, in particular and when the AC voltage supply network is ready for operation, the DC / DC converter at its first connection in a second Operating state, in particular and when a power failure is detected, i.e. failure of the AC voltage supply network, provides a second voltage, the first voltage being greater than a minimum voltage, the second voltage being less than the minimum voltage, in particular being one from the first connection of the DC / DC -Converter supplied change judge is switched off when the voltage applied to this first connection is less than the minimum voltage. A method for operating a system with a supply module, an inverter, a DC / DC converter, an energy store and a power supply unit, the DC voltage side connection of the supply module having a rectifier being electrically connected in parallel to the DC voltage side connection of the inverter and to the first connection of the DC / DC converter, to the second connection of which the energy store is connected, the AC voltage side connection of the rectifier being fed by an AC voltage supply network, with a low voltage, in particular 24 volts, the supply module, the DC / DC converter and from a first DC voltage side connection of the power supply unit is fed to the inverter, an AC voltage side connection of the power supply unit being fed from the AC voltage supply network, a second DC voltage side connection of the power supply unit parallel to the DC voltage side connection of the supply s module is connected, the DC / DC converter is designed in such a way that - in a first operating state, in particular and when the AC voltage supply network is ready for operation, the DC / DC converter provides a first voltage at its first connection, and - in a second operating state, in particular and when a power failure is detected, that is, failure of the AC voltage supply network, the DC / DC converter provides a second voltage at its first connection, the first voltage being greater than a minimum voltage, in particular 400 Volts, the second voltage being less than the minimum voltage, the inverter being switched off when the voltage applied to its terminal on the DC voltage side is less than the minimum voltage. Procedure according to Claim 1 or 2 , characterized in that sensors for power failure detection are arranged in the supply module and the supply module is connected to the DC / DC converter for data exchange. Procedure according to Claim 1 , 2 or 3 , characterized in that, to discharge the energy store, a temporally constant electrical power P is continuously supplied to the resistor R, in particular during a period of time T, in particular until the resistor is almost completely discharged, in particular where the period of time T is greater than the time constant of the through a constant electrical continuous power supplied to the resistor causes the temperature of the resistor R to rise. Procedure according to Claim 1 or 2 , characterized in that the voltage U applied to a series circuit formed from the resistor and a controllable semiconductor switch, in particular a brake chopper, is detected, the series circuit being either fed directly from the voltage made available by the energy store or via a DC / DC -Converter is fed from the voltage made available by the energy store, the controllable semiconductor switch being supplied with a pulse-width-modulated control signal with a pulse-width modulation ratio that is dependent on the value of the detected voltage, in particular where the pulse-width modulation ratio according to (1 / U) * (P * R) ^ ½ is determined, in particular the controllable half-liter switch being closed permanently when the voltage U falls below a threshold value, in particular where the threshold value is (P * R) ^ ½. Method according to one of the preceding claims, characterized in that the system has a supply module comprising a mains-fed rectifier, the DC voltage side connection of which is connected to the DC voltage side connection of an inverter and to the first connection of a DC / DC converter, the second connection being the DC / DC converter is connected to the connection of the energy store providing the voltage U, an electric motor, in particular a three-phase motor, being connected to the connection on the AC voltage side of the inverter. Method according to one of the preceding claims, characterized in that a DC / DC converter is arranged between the DC voltage side connection of the rectifier and the DC voltage side connection of the supply module, which stops the power flow from the rectifier to the series circuit formed from resistor R and controllable half-liter switch during the Discharge of the energy store, in particular so that on that power module on which the diodes of the rectifier and the controllable half-liter switch are integrated, heat is generated during discharge by either the controllable semiconductor switch or alternatively by the diodes of the rectifier. Method according to one of the preceding claims, characterized in that the inverter has a power module on which controllable semiconductor switches arranged in half bridges are arranged, and / or that the power P is less than the maximum from the electric motor via the inverter to the DC-side connection of the inverter in the regenerative operation of the electric motor, and / or that the pulse width modulation frequency of the control signal is changed during the supply of the power P, in particular during the time period T, in particular different, in particular discrete values are used as the pulse width modulation frequency in succession. Method according to one of the preceding claims, characterized in that the current I flowing through the resistor R is detected, the current resistance value of the braking resistor being determined from the time-averaged voltage provided via the brake chopper and the time-averaged current, in particular according to U / I, and taking into account a characteristic that represents the temperature dependency of the braking resistor, the current temperature T of the respective braking resistor is determined. Method according to one of the preceding claims, characterized in that it is monitored whether the specific temperature T des Braking resistance exceeds a threshold value, in particular wherein an emergency shutdown of the brake chopper is carried out after exceeding. Method according to one of the preceding claims, characterized in that the specific temperature is regulated to a setpoint temperature by setting the power P as a control value of a controller, in particular a PI controller. System, in particular for carrying out a method according to one of the preceding claims, with a supply module, an inverter, a DC / DC converter, an energy store and a power supply unit, wherein the DC voltage side connection of the supply module having a rectifier is electrically connected in parallel to the DC voltage side connection of the inverter and to the first connection of the DC / DC converter, to whose second connection the energy store is connected, wherein the AC voltage side connection of the rectifier is fed from an AC voltage supply network, wherein a low voltage, in particular 24 volts, is fed to the supply module, the DC / DC converter and the inverter from a first DC voltage-side connection of the power supply unit, an AC voltage-side connection of the power supply unit is fed from the AC voltage supply network, wherein a second DC voltage-side connection of the power supply is connected in parallel to the DC-side connection of the supply module, in particular so that the power supply can be supplied from the AC voltage supply network and / or via the DC / DC converter from the energy store, wherein the DC / DC converter is designed so that the DC / DC converter provides a first voltage at its first connection in a first operating state, in particular and when the AC voltage supply network is ready for operation, and the DC / DC converter provides a second voltage at its first connection in a second operating state, in particular and when a mains failure is detected, i.e. failure of the AC voltage supply network, the first voltage being greater than a minimum voltage, in particular 400 volts, the second Voltage is less than the minimum voltage, in particular, the inverter being designed in such a way that the inverter is switched off when the voltage applied to its DC voltage-side connection is less than the minimum voltage. System according to one of the preceding claims, characterized in that sensors for network failure detection are arranged in the supply module and the supply module is connected to the DC / DC converter for data exchange. System according to one of the preceding claims, characterized in that the system has a supply module comprising a mains-fed rectifier, the DC voltage side connection of which is connected to the DC voltage side connection of an inverter of the system and to the first DC voltage side connection of a DC / DC converter of the system, wherein the second DC voltage-side connection of the DC / DC converter is connected to the energy storage device, in particular a battery arrangement and / or double-layer capacitor arrangement and / or ultracap arrangement, an electric motor, in particular a three-phase motor, being connected to the AC voltage-side connection of the inverter. System according to one of the preceding claims, characterized in that a DC / DC converter is arranged between the DC voltage side connection of the rectifier and the DC voltage side connection of the supply module, and / or that a controllable semiconductor switch connected in series with the braking resistor in the housing of the DC / DC converter is arranged, and / or that a controllable semiconductor switch connected in series with the braking resistor is integrated on a power module, which has diodes and / or controllable semiconductor switches arranged in half bridges, and / or that the power module is in the housing of the inverter or of the supply module is arranged.

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