DE102014211853A1 - Voltage converter and method for converting an electrical voltage - Google Patents

Abstract

The present invention provides a bidirectional voltage converter. The voltage converter comprises at least four operating modes for converting a DC voltage into a voltage for controlling an electrical machine or for converting a generator voltage into a DC voltage. The respective converted voltage is smoothed and provided with a significantly reduced noise component than with conventional current regulators. The circuit construction in particular allows operation with high switching frequencies. Thus, the switching frequency can be shifted to an area beyond the human hearing range. In addition, high switching frequencies also allow a reduction in weight and the required installation space for the voltage converter.

Description

The present invention relates to a voltage converter and a method for converting an electrical voltage.

Electric propulsion systems, such as used in electrically powered vehicles, may be powered by, for example, a DC power source, such as a high power traction battery. The DC voltage provided by this battery must be converted by means of a voltage converter (inverter) into a single-phase or multi-phase AC voltage in order to be able to generate the desired torque on the electric machine. Current inverters for electric drive systems in this case use the principle of pulse width modulation (PWM) via thyristor, IGBT or MOSFET power half-bridges with a corresponding number of phases to be realized. By modulating the duty cycle of the half-bridges assigned to the phases, a current value is generated by the machine windings in interaction with the motor inductances, which causes a corresponding moment in the machine rotor. By a suitable control of the half bridges thus driving pattern can be generated with rotating field character with variable fundamental frequencies, phase relationships and modulation degrees. Due to the inclusion of the motor inductance is achieved so that an arrangement with a low number of components with high efficiency.

In such circuit topologies, a pulse width modulated signal is fed to the electric machine by the inverter. To avoid electromagnetic interference, the cable connections received must be sufficiently shielded. Due to the physical characteristics and power dissipation limit of the switching elements used in the current inverters, the PWM switching frequencies are typically limited to low frequencies in the human listening range (up to 20 kHz).

The German patent application DE 10 2013 201 538 A1 discloses an inverter system for reducing unwanted noise generated due to PWM drive in an electric vehicle. For this purpose, the electric motor is controlled with an optimized, pseudorandom periodic grid.

The voltage supply of a conventional inverter is usually initially limited to the current battery or source voltage. If higher voltages are required, for example, to expand the speed range, then the DC voltage must be adjusted via a step-up converter circuit.

There is a need for an efficient and inexpensive voltage conversion suitable for driving an electrical machine.

Disclosure of the invention

To this end, according to one aspect, the present invention provides a voltage converter with a DC voltage connection comprising a first connection element and a second connection element; a machine terminal comprising a third terminal and a fourth terminal; a conversion device configured to convert a DC voltage between the first terminal and the second terminal to a phase voltage for an electric machine and to provide the converted phase voltage between the third terminal and the fourth terminal and further configured to be one of convert the phase voltage provided between the third terminal and the fourth terminal into a predetermined DC voltage and provide the converted DC voltage between the first terminal and the second terminal; wherein in a first mode of operation, the conversion device converts the DC voltage between the first terminal and the second terminal into a phase voltage whose maximum value is greater than the DC voltage between the first terminal and the second terminal, in a second operating mode, the DC voltage between the first terminal and second terminal is converted into a phase voltage whose maximum value is smaller than the DC voltage between the first terminal and the second terminal, in a third operating mode, the phase voltage between the third terminal and the fourth terminal converted into the predetermined DC voltage, wherein the maximum value of the phase voltage is smaller as the predetermined DC voltage, and in a fourth mode of operation, the phase voltage between the third terminal and the fourth terminal in the predetermined DC voltage is converted, wherein the maximum value of the phase voltage is greater than the predetermined DC voltage.

According to another aspect, the present invention provides a method of converting an electrical voltage with the steps of providing a voltage converter according to the invention; of selecting one Operation mode; and driving the voltage converter in dependence on the selected operating mode.

Advantages of the invention

It is an idea of the present invention to design a voltage converter between a DC voltage source and an electric machine such that a bidirectional voltage conversion can take place between both sides. At the same time, the voltage converter according to the invention provides step-up and step-down functionalities in both forward and reverse directions. This provides a compact and highly efficient voltage converter for a very wide range of applications.

By integrating boost and buck converter functionality to expand the voltage level of the source voltage, the voltage converter can be used in a very wide range of applications. In this way, output voltages over the entire operating voltage range up to a minimum voltage of 0 volts are possible. This allows the operation of an electric machine in a very wide speed range due to the high variability of the output voltage of the voltage converter, regardless of the source voltage of the DC voltage source.

The bidirectional voltage conversion in combination with the stepping up or down of the voltage level also allows the kinetic energy to be fed back into a DC battery during a deceleration process by means of a regenerative electric machine. In this case, in particular due to the integrated boost converter functionality, even with low output voltages of the regenerative electric machine, there is still a return of the energy into the battery. Thus, during braking, a particularly efficient recovery of kinetic energy can take place.

According to one embodiment, the conversion device comprises a first switching element, which is arranged between the first connection point and a first node, and a second switching element, which is arranged between the first node point and the second connection element. The conversion device further includes a third switching element disposed between the third terminal and a second node and a fourth switching element disposed between the second node and the fourth terminal. Furthermore, the conversion device comprises an inductance, which is arranged between the first node and the second node. By integrating an inductance in the conversion device, it is not necessary to include the motor inductance for the voltage conversion. Thus, the voltage conversion can be done entirely within the conversion device. Therefore, at the machine connection of the voltage converter is a trouble-free, or at least significantly less interference output signal. A shielding of the electrical connection between the machine connection of the voltage converter and electrical machine is therefore generally not required. Instead, an already smoothed output voltage with the machine fundamental frequency is available at the machine connection of the voltage converter.

Preferably, the conversion device is operated at a switching frequency of at least 20 kHz. Such switching frequencies are above the human audible range. Thus, the acoustic interference by audible vibrations can be avoided or at least significantly reduced. Furthermore, such high switching frequencies allow miniaturization of the circuitry. In particular, the inductances used can be made smaller at higher switching frequencies.

According to one embodiment, the voltage converter further comprises a control device configured to drive the first, the second, the third and the fourth switching element in dependence on a selected operating mode. This allows flexible control of the voltage converter in all operating modes.

According to another embodiment, the conversion device is further configured to close the third switching element and the fourth switching element in a fifth operating mode. As a result, the third connection element and the fourth connection element are electrically connected to one another at the machine connection. Thus, a connected electric machine can be switched into an active short circuit in this operating mode. The voltage converter can also open in a further operating mode, the third switching element and the fourth switching element, in order to switch a connected electric machine in the operating mode of the freewheel.

According to a further embodiment, the phase voltage provided between the third connection element and the fourth connection element is an alternating voltage, in particular a sinusoidal voltage between the potential of the third connection element and one, from the operating mode and a predetermined PWM. Ratio resulting maximum potential of the fourth connection element.

According to a further embodiment, the method according to the invention determines a DC voltage at the DC voltage connection of the voltage converter and / or a phase voltage at the motor connection of the voltage converter. The step of selecting the operation mode then selects the operation mode using the detected DC voltage and / or the detected phase voltage.

According to a further aspect, the present invention comprises an electric drive system with a voltage converter according to the invention. The electric drive system may further comprise an electrical machine having a phase connection, the phase connection being electrically coupled to the machine terminal of the voltage converter. Further, the electric drive system may include an electrical energy storage, which is electrically coupled to the DC voltage terminal of the voltage converter.

According to a further embodiment, the electric machine is a multi-phase electric machine, in particular an at least two-phase machine. In this case, the electric drive system comprises at least one voltage converter for each phase of the electric machine.

According to one embodiment, the electrical drive system may comprise a plurality of voltage converters connected in parallel for each phase of an electrical machine.

According to a further aspect, the present invention comprises a motor vehicle, aircraft or ship with an electric drive system according to the invention.

Brief description of the drawings

Further embodiments and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. Showing:

1 : a schematic representation of a circuit arrangement of a voltage converter according to an embodiment;

2 a schematic representation of an electric drive system with a voltage converter according to an embodiment;

3 a schematic representation of an electric drive system with a voltage converter according to another embodiment;

4 a schematic representation of an electric drive system with a voltage converter according to yet another embodiment;

5 a schematic representation of a motor vehicle with an electric drive system according to an embodiment; and

6 : A schematic representation of a method for converting an electrical voltage, as it is based on an embodiment.

Description of embodiments

1 shows a schematic representation of a circuit arrangement for a voltage converter 1 as it is based on an embodiment. The voltage converter 1 includes a DC voltage connection 11 , a machine connection 12 , a conversion device 13 and a control device 14 , The DC voltage connection 11 can with a DC voltage source 2 , For example, a battery connected. In this case, a first connection element A1 with a pole of the DC voltage source 2 connected and a second connection point A2 connected to the other pole of the DC voltage source. Furthermore, the voltage converter has 1 via a machine connection 12 with a third connection element A3 and a fourth connection element A4. In the single-phase embodiment shown here, the two connection elements A3 and A4 of the machine connection 12 with the phase connections of an electrical machine 3 get connected. The voltage converter 1 further comprises a conversion device 13 The switching elements S1 to S4 may be, for example, semiconductor switches T1 to T4, to which preferably a free-wheeling diode D1 to D4 is connected in parallel. As a semiconductor switch, for example, thyristors, bipolar transistors with an insulated gate (IGBT) or MOSFET are possible. In particular silicon carbide switches (SiC) or super junction MOSFETs are particularly suitable for high switching frequencies, in which switching frequencies of 20 kHz and more can be realized with only very low switching losses.

The first switching element S1 is in this case between the first connection element A1 of the DC voltage connection 11 and a first node K1 arranged. The second switching element S2 is between this first node K1 and the second connection element A1 of DC connection 11 arranged. Furthermore, the third switching element S3 between the third connection element A3 of the machine connection 12 and a second node K2. The fourth switching element S4 is between the second node K2 and the fourth connection element A4 of the machine connection 12 arranged. Between the first node K1 and the second node K2, an inductance L is arranged. The second connection point A2 of the DC voltage connection 11 and the fourth connection element A4 of the machine connection 12 can also be electrically connected to each other and are preferably at the reference potential of the voltage converter 1 ,

For controlling the switching elements S1 to S4, the control terminals of these switching elements S1 to S4 with a control device 14 get connected. The control device 14 can be designed to control signals and / or setpoints for the operation of the electrical machine 3 to recieve. Based on these control signals and / or set values, the control device outputs 14 Switching signals to the switching elements S1 to S4 from to open or close the corresponding switching elements S1 to S4. The control signals or setpoints can be via analog or digital signals to the control device 14 to be provided. For example, the corresponding control signals or setpoint values can be transmitted via a bus system and by the control device 14 be received.

Furthermore, the control device 14 also measurements of the voltage at the DC voltage connection 11 and / or at the machine connection 12 receive. For example, this voltage sensors 15 . 16 at the DC voltage connection 11 and / or at the machine connection 12 are arranged, which determine the corresponding voltages and the measured values of the determined voltages to the control device 14 transfer. Alternatively, existing sensors can also transmit their measured values to the control device 14 transmit information about the voltage at the DC voltage port 11 and / or at the machine connection 12 the control device 14 provide.

Depending on the control of the switching elements S1 to S4 in the conversion device 13 of the voltage converter 1 Thus, different operating modes can be realized. In a first operating mode, the voltage converter operates 1 as a combined boost converter inverter. The at the DC voltage connection 11 applied DC voltage is thereby raised and simultaneously converted into a voltage which is suitable for an electrical machine on the machine connection 12 head for. In boost converter mode, this is the maximum value, that is to say the amplitude of the voltage at the machine connection 12 greater than the DC voltage at the DC voltage port 11 is applied.

For this purpose, the first switching element S1 by the control device 14 controlled so that it is permanently closed. Furthermore, the second switching element S2 is permanently opened. The third switching element S3 is driven as an active rectifier, so that flows through the freewheeling diode D3 and possibly also by the semiconductor switch T3, the current only in one direction. Finally, the fourth switching element S4 is driven with a predetermined switching frequency. In this case, according to the principle of the pulse width modulation according to the duty cycle, the voltage on the side of the machine connection 12 set. In this case, there is between input voltage U1 at the DC voltage connection 11 and output voltage U2 at the machine connection 12 the following relationship: U2 / U1 = T / (T - t _a).

In this case, T is the period of the predetermined switching frequency f with which the control device 14 the fourth switching element S4, and drives each t _a the time within a period duration T, during which the switching element S4 is closed. An output voltage U2 T of 50% are achieved at double the input voltage U1: As can be seen here, can _already at a duty cycle t.

In a second operating mode, the voltage converter operates 1 as a combined buck converter inverter. The at the DC voltage connection 11 applied DC voltage is thereby reduced and simultaneously converted into a voltage which is suitable for an electrical machine at the machine connection 12 head for. In buck converter mode is the maximum value, ie the amplitude of the voltage at the machine connection 12 less than the DC voltage at the DC voltage port 11 is applied.

In this case, the third switching element S3 is permanently closed and the fourth switching element S4 permanently open. The second switching element S2 is driven as an active rectifier, which allows only a current flow in one direction in this mode. The first switching element S1 is finally driven with the predetermined switching frequency f = 1 / T such that at the machine connection 12 sets the desired output voltage U2. The ratio of output voltage U2 to input voltage U1 is as follows: U2 / U1 = t _on / T.

It is easy to see from this formula that the step-down converter mode, the output voltage U2 can be down to 0 volts lowered when t _one goes to zero.

In addition to the operating modes described above, in which a DC voltage at the DC voltage connection 11 in a voltage for controlling an electrical machine 3 is also a conversion of the machine connection 12 applied voltage of a generator operated electric machine 3 in a DC voltage with a predetermined height possible. The voltage U2 coming from the electric machine 3 at the machine connection 12 can be varied, and be greater or less than the DC voltage at the DC voltage terminal 11 should be provided to there an electrical energy storage 2 to feed and, for example, charge a battery.

Is the amplitude or the maximum value of the voltage U2 at the machine connection 12 of the voltage converter 1 smaller than that for charging the electrical energy storage 2 required DC voltage U1, the voltage converter works 1 in a further operating mode as a combined rectifier and boost converter. For this purpose, the third switching element S3 is permanently closed and the fourth switching element S4 permanently open. The first switching element S1 operates as an active rectifier, which transmits the current in one direction only, and the second switching element S2 is clocked at a predetermined switching frequency. Thus arises at the DC voltage connection 11 a voltage U1 according to the following formula: U1 / U2 = T / (T - t _a).

Is the maximum value or the amplitude of the electrical machine 3 provided voltage U2 at the machine connection 12 greater than the voltage U1, with the electrical energy storage 2 is to be charged, so the voltage converter works 1 in a further operating mode as a combined rectifier and buck converter. For this purpose, the first switching element S1 is permanently closed and the second switching element permanently open. The fourth switching element S4 operates as an active rectifier, which only transmits the current in one direction, while the third switching element S3 is clocked at the predetermined switching frequency f = 1 / T. This adjusts the stress ratios according to the following formula: U1 / U2 = _a / t T.

In addition, it is with the previously described voltage converter 1 also possible, the electric machine 3 to switch to a safe operating state, such as the active short circuit or a freewheeling mode.

For the active short circuit, the first and second switching elements S1 and S2 are opened for this purpose, and the third switching element S3 and the fourth switching element S4 are closed. Thus are at the machine connection 12 the third connection element A3 and the fourth connection element A4 are electrically connected to one another and thus the phase connections of the electrical machine 3 shorted.

If, on the other hand, the third switching element S3 and the fourth switching element S4 are open at the same time, then the electric machine is located 3 in freewheel mode.

The control of the switching elements S1 to S4 of the conversion device 13 of the voltage converter 1 through the control device 14 By means of the formula described above, this can be done by means of a suitable microcontroller. With appropriate existing computing power, the duty cycle of the switching elements S1 to S4 to be switched can take place via suitable mathematical algorithms. Alternatively, it is also possible to calculate the required duty cycles in advance and in a memory of the control device 14 save. In this way, the control device 14 be relieved.

The switching frequency with which the switch elements S1 to S4 are driven can be selected in a very wide frequency range. Analogous to conventional inverters, for example, switching frequencies in the range up to 10 kHz are possible. However, relatively low switching frequencies require a relatively large inductance L between the first node K1 and the second node K2. By increasing the switching frequency to frequencies above 20 kHz and more, the required inductance L can be correspondingly reduced. This leads to a further reduction of the required installation space and the weight of the voltage converter 1 , In addition, the use of switching frequencies above the human hearing range also leads to a lower acoustic impairment. For the use of such high switching frequencies of 20 kHz and more, in particular modern silicon carbide (SiC) switches are advantageous. Such SiC switches have relatively low switching losses even at switching frequencies above 20 kHz. Alternatively, it is also possible to use voltage converters with a super-junction MOSFET, which also have only low switching losses at high switching frequencies.

The embodiment described above describes for a better understanding of an electric drive voltage converter 1 , electrical energy storage 2 and a single-phase electric machine 3 , In addition, the voltage converter 1 also for electric drives with multiphase electrical machines 3 be used. In the following, therefore, are circuit configurations for a three-phase electric machine 3 executed. The choice of three phases for a multi-phase electric machine 3 serves only for illustrative purposes. In addition, electrical machines with any other number of phases are also possible.

2 shows a schematic representation of a circuit concept of a three-phase electric machine 3 with mass star point. Each of the three phases L1, L2, L3 is in this case with a connection element, for example the third connection element A3 of the machine connection 12 a previously described conversion device 13 electrically connected. The respective other connection element, that is, for example, the fourth connection element A4 is electrically connected to the reference potential. The neutral point of the electric machine 3 is also electrically connected to the reference potential. On the DC side are all DC voltage connections 11 from a common electrical energy storage 2 fed. The switching elements of all conversion devices 13 can by a common control device 14 be controlled. In addition, it is also possible that for each phase a separate control device 14 is available.

3 shows a further schematic representation of an electric drive with a three-phase electric machine 3 , In this embodiment, a three-phase system structure is shown with a virtual mass star point. That is, the windings of all phases of the electric machine 3 are electrically connected at the star point. However, this star point is not electrically connected to a reference potential. Otherwise, the structure of the electric drive with virtual mass star point is analogous to the structure of the electric drive with mass star point, in which the mass star point is at reference potential.

4 shows a schematic representation of an electric drive with a three-phase electric machine in delta connection. The windings of the electric machine 3 are each between two phase terminals of the electric machine 3 connected. In addition, the structure of the electrical energy source 2 as well as the used voltage converter 1 analogous to the previously described embodiments.

5 shows a schematic representation of a motor vehicle with an electric drive. The electric drive from electrical energy storage 2 , the voltage converters 1 as well as the electric machine 3 can be carried out, for example, according to one of the embodiments described above.

6 shows a schematic representation of a flowchart, as a method 100 for converting an electrical voltage according to one embodiment is based. In one step 110 First, a previously described voltage converter 1 provided. Then in step 120 an operating mode is selected. This operating mode can be, for example, the above-described operating modes boost converter inverters, the buck converter inverters, boost converter rectifier, buck converter rectifier. In addition, the safe operating mode in the form of an active short circuit or free-running mode is possible.

Then in step 130 the voltage converter 1 controlled depending on the selected operating mode.

The selection of the operating mode may be in accordance with the previously received setpoint specifications for a torque of the electric machine 3 be determined. Alternatively, instead of the torque, an electric current in the phase or phases of the electric machine 3 by providing the output voltage at the motor terminal 12 of the voltage converter is to be set. Should the electric machine 3 delayed, for example, to decelerate an electrically driven motor vehicle, so a corresponding braking torque can be specified. Furthermore, the operating mode of the active short circuit or of the freewheeling mode can also be specified for setting a safe operating mode. Furthermore, the voltage conditions at the machine connection 12 or the DC voltage connection 11 be determined. In this way it is in particular possible to determine whether the voltage converter 1 in the boost converter mode or in the buck converter mode to be operated. Furthermore, there is thus also a precise control for adjusting the voltage conditions at the DC voltage connection 11 or at the machine connection 12 possible.

For this purpose, for example, in step 115 the size of the DC voltage at the DC voltage connection 11 of the voltage converter 1 be determined. Additionally or alternatively, the size of the phase voltage at the motor connection 12 of the voltage converter 1 be determined. Based on the determined voltages, in step 130 then the operating mode using the determined DC voltage and / or the determined phase voltage can be selected.

In summary, the present invention relates to a bidirectional voltage converter. The voltage converter comprises at least four operating modes for converting a DC voltage into a voltage for controlling an electrical machine or for converting a generator voltage into a DC voltage. The respective converted voltage is smoothed and provided with a significantly reduced noise component than with conventional current regulators. The circuit construction in particular allows operation with high switching frequencies. Thus, the switching frequency can be shifted to an area beyond the human hearing range. In addition, high switching frequencies also allow a reduction in weight and the required installation space for the voltage converter.

QUOTES INCLUDE IN THE DESCRIPTION

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

Cited patent literature

• DE 102013201538 A1 [0004]

Claims (10)

Voltage converter ( 1 ), comprising: a DC voltage connection ( 11 ) comprising a first terminal member (A1) and a second terminal member (A2); a machine connection ( 12 ) comprising a third terminal (A3) and a fourth terminal (A4); and a conversion device ( 13 ), which is designed to convert a predetermined DC voltage (U1) between the first connection element (A1) and the second connection element (A2) into a phase voltage (U2) for an electrical machine ( 3 ) and to provide the converted phase voltage (U2) between the third terminal element (A3) and the fourth terminal element (A4), and which is further adapted to one of the electric machine ( 3 ) to convert phase voltage (U2) provided between the third connection element (A3) and the fourth connection element (A4) into a predetermined direct voltage (U1) and the converted direct voltage (U1) between the first connection element (A1) and the second connection element (A2) provide; the conversion device ( 13 In a first operating mode, the DC voltage (U1) between the first connection element A1) and the second connection element (A2) is converted into a phase voltage (U2) whose maximum value is greater than the DC voltage (U1) between the first connection element (A1) and the second terminal element (A2), in a second operating mode, the DC voltage (U1) between the first terminal element (A1) and the second terminal element (A2) converted into a phase voltage (U2) whose maximum value is smaller than the DC voltage (U1) between the first Terminal element (A1) and the second connection element (A2), in a third operating mode, the phase voltage (U2) between the third terminal element (A3) and the fourth connection element (A4) in the predetermined DC voltage (U1) converted, wherein the maximum value of the phase voltage ( U2) is less than the predetermined DC voltage (U1), and in a fourth mode of operation, the phase voltage (U2) between the third Terminal element (A3) and the fourth connection element (A4) in the predetermined DC voltage (U1) is converted, wherein the maximum value of the phase voltage (U2) is greater than the predetermined DC voltage (U1). Voltage converter ( 1 ) according to claim 1, wherein the conversion device ( 13 ) comprises: a first switching element (S1) disposed between the first terminal (A1) and a first node (K1); a second switching element (S2) disposed between the first node (K1) and the second terminal (A2); a third switching element (S3) disposed between the third terminal (A3) and a second node (K2); a fourth switching element (S4) disposed between the second node (K2) and the fourth terminal (A4); an inductance (L) disposed between the first node (K1) and the second node (K2). Voltage converter ( 1 ) according to claim 2, wherein the voltage converter ( 1 ) a control device ( 14 ) configured to drive the first, second, third and fourth switching elements (S1-S4) in response to a selected operating mode. Voltage converter ( 1 ) according to one of claims 1 to 3, wherein the conversion device ( 13 ) is further configured to close the third switching element (S3) and the fourth switching element (S4) in a fifth operating mode to electrically connect the third terminal element (A3) and the fourth terminal element (A4). Voltage converter ( 1 ) according to one of claims 1 to 4, wherein the phase voltage (U2) provided between the third connection element (A3) and the fourth connection element (A4) is an alternating voltage. An electric drive system, comprising: a voltage converter according to any one of claims 1 to 5; an electrical energy store ( 2 ) connected to the DC voltage connection ( 11 ) of the voltage converter ( 1 ) is electrically coupled; and an electric machine ( 3 ) comprising a phase connection connected to the machine connection ( 12 ) of the voltage converter ( 1 ) is electrically coupled. Electric drive system according to claim 6, wherein the electric machine ( 3 ) comprises a multi-phase electric machine, and the electric drive system for each phase of the electric machine ( 3 ) at least one voltage converter ( 1 ). Motor vehicle, in particular, air, water or land vehicle, with an electric drive system according to claim 6 or 7. Procedure ( 100 ) for converting an electrical voltage, comprising the steps of: providing ( 110 ) of a voltage converter ( 1 ) according to any one of claims 1 to 5; Choose ( 120 ) of an operating mode; and driving ( 130 ) of the voltage converter ( 1 ) depending on the selected operating mode. Procedure ( 100 ) according to claim 9, comprising the step of: determining ( 115 ) of a DC voltage at the DC voltage terminal ( 11 ) of the voltage converter ( 1 ) and / or determining a phase voltage at the motor terminal ( 12 ) of the voltage converter ( 1 ); the step ( 120 ) selects the operating mode using the determined DC voltage and / or the determined phase voltage to select the operating mode.

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