METHOD FOR OPERATING A PLANT

Description

[0001] The invention relates to a method for commissioning a system comprising two actuators. The actuators are each electrically connected to a common DC voltage circuit via a converter.

[0002] Systems, such as industrial plants, typically have multiple actuators used to create and / or process a workpiece. The actuators themselves typically include at least one electric motor, which drives another component of the respective actuator. To reduce wear on the electric motor and increase efficiency, a brushless electric motor is typically used. Therefore, a converter, which acts as an inverter, is required to supply power to the electric motor.

[0003] Such converters usually comprise a bridge circuit with several bridge arms connected between two electrical potentials. The two electrical potentials are usually constant, so that a direct current is applied between them. Each of the bridge arms has a bridge output to which an electrical phase of the electric motor is connected, provided the converter is used to operate an electric motor. The converter therefore has as many bridge outputs and therefore bridge arms as the electric motor has phases. If the electric motor has three phases, the converter consequently comprises three bridge arms and is usually implemented using a B6 circuit or at least includes one. Usually, each bridge arm has two switches connected electrically in series, with the series circuit being connected between the two electrical potentials.A tap is formed between the two switches, which is connected to the respective bridge output.

[0004] Due to the principle behind the converter, only one of the two electrical potentials can be applied to each bridge output during operation, resulting in an electrical current flow through the respective phase. However, in order for the electric motor to operate at a specific power level, the electrical current carried by each phase and thus the electrical potential applied to each phase must be varied. Since the level of the electrical potential cannot be changed, this is achieved via the time average, so that a time-modulated electrical potential is applied.

[0005] For this purpose, for example, pulse-width modulation is used, in which the length of time one of the potentials is applied to the respective bridge output depends on a desired signal, namely the power requirement. Typically, the desired signal is compared with a periodic carrier signal. If the desired signal is above the carrier signal, one of the potentials is applied, and otherwise the other potential is applied. Pulse-width modulation enables comparatively precise control of the electric motors. However, with every change in the electrical potential applied to the bridge output, an electrical recharging current occurs due to existing capacitances, such as cable capacitances, in the system.

[0006] Each converter is typically powered by a DC voltage circuit, which provides the two electrical potentials. For example, each converter is assigned a corresponding DC voltage circuit, which is powered by a respective rectifier that is electrically connected to a power grid, for example. To save costs, however, only a single DC voltage circuit is usually provided, which is powered by a single rectifier from the power grid and which operates all converters. As a result, manufacturing costs are reduced.

[0007] To ensure coordinated operation of the actuators, the associated converters are typically operated with the same carrier signal. This also reduces the complexity of the system. However, if the actuators are also operated according to the same wanted signal / power requirement, the electrical recharging currents occur at the same time and add up, resulting in a comparatively high load on the DC voltage circuit or, via any rectifier, back into the supply grid. To prevent this, chokes are usually provided, which on the one hand increases manufacturing costs. On the other hand, it reduces the system's efficiency.

[0008] EP 3 425 786 A1 discloses a power converter system comprising a power source and a plurality of voltage source converters for driving respective loads. The plurality of voltage converters is connected to the power source via a common DC link.

[0009] DE 10 2020 106 624 A1 discloses a control circuit for an electric motor, comprising a first clocked converter having three output terminals and configured to provide a first pulse-width-modulated voltage signal at each output terminal. Furthermore, a second clocked converter having three output terminals and configured to provide a second pulse-width-modulated voltage signal at each output terminal is provided.

[0010] WO 2019 / 075104 A1 discloses a variable-speed drive configured to supply power to a motor. The drive comprises a first power unit configured to supply a first power to the motor and a second power unit configured to supply a second power to the motor.

[0011] The invention is based on the object of specifying a particularly suitable method for commissioning a system as well as a system, wherein manufacturing costs are advantageously reduced and / or a load is reduced.

[0012] With regard to the method for commissioning a system, this object is achieved according to the invention by the features of claim 1 and with regard to the system by the features of claim 2. Advantageous further developments and refinements are the subject of the respective subclaims.

[0013] The method is used to commission a system that has a direct current circuit. During operation, a direct current is applied to the direct current circuit, and the direct current circuit comprises two mutually different electrical potentials. For example, the direct current circuit is fed by a voltage source, such as a battery. Alternatively, the direct current circuit is fed by a supply network, which, for example, provides an alternating current. A rectifier, preferably designed as a bridge rectifier, is expediently arranged between the supply network and the direct current circuit. For example, the rectifier is uncontrolled and, in particular, is a diode rectifier.Alternatively, the rectifier is controlled, making it possible to adjust the DC voltage applied to the DC circuit and / or feed electrical energy from it back into the supply grid. In summary, during operation, the DC circuit has a DC voltage that is generally greater than 10 V. For example, the DC voltage is between 200 V and 600 V. This makes it possible to use a three-phase AC network as the supply grid.

[0014] The system also includes two actuators, each of which is electrically connected to the DC voltage network via a converter. Thus, each actuator is assigned one of the converters, which is used to electrically connect the DC voltage circuit. Consequently, the actuators can be operated via the converters, with the individual actuators being powered from the DC voltage circuit.

[0015] The converters are, for example, inverters, so that the individual actuators are supplied with a respective (electrical) alternating voltage. Due to the two converters, independent operation of the two actuators is also possible. The converters make it possible to operate the individual actuators according to a specific useful signal that corresponds to or at least matches a power requirement, so that the individual actuators can be operated with different power levels. In particular, the two actuators are each formed by an electric motor or, for example, each have a corresponding electric motor. The electric motor(s) are preferably synchronous or asynchronous three-phase motors and / or brushless.

[0016] The respective useful signal is, in particular, a specific speed and / or torque, or some other power generated by the respective actuator, based on which the electrical voltage applied to the respective actuator is adjusted by the respective converter. The applied electrical voltage, for example, results in a specific electrical current flow, so that the actuators are operated according to the respective useful signal, i.e., the power requirement.

[0017] The system is, for example, a component of a motor vehicle, such as a commercial vehicle or passenger car. In another alternative, the motor vehicle is, for example, a construction vehicle or an agricultural implement. In this case, each of the actuators is assigned to a wheel of the motor vehicle, or, for example, one of the actuators is assigned to the main drive of the motor vehicle and the remaining actuator to an auxiliary unit of the motor vehicle.

[0018] However, the system is particularly preferably an industrial system and thus stationary. For example, during operation, a workpiece is processed, moved, and / or created by means of each of the actuators. For this purpose, each of the actuators carries, or is at least capable of carrying, a maximum electrical current of more than 1000 A, 2000 A, 3000 A, or 4000 A. Suitably, the two actuators are assigned to a press, and the actuators press two rams, which are guided so as to be movable relative to one another, against one another, thereby compressing an object located between them.

[0019] For example, the two actuators may be identical in design or different in construction. For example, the two actuators are separate electric motors, or the two actuators are assigned to the same electric motor, so that each of the actuators forms a sub-motor, in particular a part of a stator. Consequently, the electric motor, which comprises the two sub-motors, is operated with two inverters. In particular, the electric motor is designed with four windings.

[0020] The system is to be operated according to a method which provides, in particular, that a useful signal is first provided or received for each of the two actuators. Based on the respective useful signal for the respective actuator, a pulse-width-modulated signal is created using a respective periodic carrier signal. In other words, the respective useful signal, which may be analog in design, is converted by means of the respective periodic carrier signal into the pulse-width-modulated signal, which is in particular a binary signal, i.e. a digital signal. In this case, the same carrier signal is used to convert the two useful signals, whose period is therefore the same. Consequently, the creation of the two carrier signals used is simplified.

[0021] For example, when converting the respective wanted signal into the pulse-width-modulated signal, the respective wanted signal is compared with the respective carrier signal. If the wanted signal is greater than the carrier signal, the (current) value of the pulse-width-modulated signal is used, for example, 1 or another predetermined value. Otherwise, the value of the pulse-width-modulated signal is 0 ("zero") or another different value. In summary, each wanted signal is translated into the digital domain, and the respective wanted signal is present in each pulse-width-modulated signal. The two pulse-width-modulated signals only have a certain number of different values, such as two. In particular, each pulse-width-modulated signal has several pulses of the same height, although the length of the pulses depends on the current value of the respective wanted signal.

[0022] For example, the pulse-width modulated signals are initially set to a specific value, in particular the value 1, at the beginning of a clock cycle (period) of the respectively assigned carrier signal, and subsequently, depending on the current value of the useful signal, the length of the time period during which the value is maintained is adjusted.

[0023] In summary, there are two pulse-width-modulated signals, each of which corresponds to one of the useful signals assigned to one of the actuators. The converter assigned to the same actuator is operated according to the respectively assigned pulse-width-modulated signal to apply a corresponding electrical voltage to the respective actuator. For example, the converter is operated in such a way that each time the respective pulse-width-modulated signal has a certain value, the electrical voltage present in the DC voltage circuit is applied to the respectively assigned actuator. For the remaining value of the pulse-width-modulated signal, however, no electrical voltage is applied to the actuator, or the opposite polarity of the DC voltage circuit is applied.In summary, an electrical voltage is applied to the respective actuator, which corresponds in particular to the pulse-width-modulated signal or, for example, has the same form, but the values ​​are different. In particular, the logical value 1 of the pulse-width-modulated signal is assigned the electrical voltage applied to the DC voltage circuit, and the logical value 0 ("zero") of the pulse-width-modulated signal is assigned no electrical voltage. As a result, each of the actuators is operated according to the respective wanted signal, i.e., the respective power requirement.

[0024] Due to the application of the respective electrical voltage, an electrical current flows from the DC circuit to the respective actuator.

[0025] Every time the electrical voltage is interrupted, it is possible that a charge reversal current will occur due to capacitance.

[0026] According to the method by which the system is to be operated, it is provided that the two carrier signals are selected to be identical, i.e., in particular, they have the same shape. However, the two carrier signals are offset from each other by a predetermined phase shift. In other words, one of the carrier signals is offset in time from the other, so that they do not directly correspond. In particular, the phase shift is smaller than the period of the carrier signal, so that due to the phase shift, there is no direct mapping of the two carrier signals to each other.

[0027] Due to the phase shift, the individual pulses of the two pulse-width-modulated signals are offset from each other, so that any transfer currents do not occur simultaneously. As a result, they do not add up at the same time, but rather they have already partially decayed by the time the transfer current occurs in the other actuator, so that the maximum of the sum of the resulting transfer currents is reduced. As a result, the load is reduced. No additional components, such as chokes or the like, are required, or they can be designed with comparatively low power, thus reducing manufacturing costs. It is also possible to operate an existing system using the process.

[0028] For example, the system has more than two actuators, with each actuator assigned a corresponding converter. The generation of the respective pulse-width modulated signal, depending on the respective wanted signal, and the application of the corresponding electrical voltage are always carried out in the same way, using the same carrier signal in each case. For example, all carrier signals are phase-shifted from one another, which is why, on average, only comparatively low recharging currents occur.

[0029] However, the phase offset is particularly preferably selected to be equal to half the period of the carrier signal, regardless of the number of converters and actuators actually present. Thus, both with two such converters and actuators and with, for example, three, four, five or more converters / actuators, only a single phase offset is present, with the phase offset assigned to half of the converters / actuators and no phase offset to the others. If the number of converters / actuators is an odd number, the phase offset is either assigned to this converter / actuator or not. Due to the selection of half the period as the phase offset, the recharging currents essentially occur at the same time, but have different polarity and are thus directed in opposite directions. The resulting recharging currents therefore compensate each other.As a result, the load in the DC circuit is reduced or eliminated altogether, so that the voltage source supplying the DC circuit, such as the battery or rectifier, is essentially non-existent. Consequently, any chokes or the like are not required, thus reducing manufacturing costs. This also reduces weight. Furthermore, a comparatively simple adjustment of the phase shift is possible.

[0030] For example, the two useful signals or all of the useful signals are constant over time. However, they are particularly preferably variable over time, in particular depending on the control of the respective actuator. For example, the respective useful signal is changed at random times. However, the useful signals are particularly preferably changed simultaneously, thus enabling coordinated operation of the two actuators. Suitably, the phase offset is selected to be half the period, and the change in the useful signal occurs at one of the converters at the start of the period (of the respective clock cycle) of the associated carrier signal and at the other converter in the middle of the respective clock cycle.By choosing half the period, it is always possible to reliably determine when and / or if the change is made, and the change does not introduce any additional artifacts into the pulse-width modulated signal created in this way.

[0031] For example, the two actuators are operated using the same useful signal, which is thus changed at the same time points. The phase shift is also suitably chosen to be half the period. Thus, the resulting charge-reversal currents essentially cancel each other out, further reducing the load.

[0032] The carrier signal expediently has a frequency between 1 kHz and 20 kHz, for example, between 4 kHz or 16 kHz. For example, a frequency of 4 kHz, 8 kHz, or 16 kHz is used. This reduces the number of changes in the pulse-width-modulated signals and thus also in the applied electrical voltage and the resulting recharging currents. Furthermore, the inaccuracies resulting from the conversion of the analog wanted signal into the pulse-width-modulated signal are comparatively small. This also allows for a comparatively rapid conversion / accounting for a change in the wanted signal.

[0033] For example, a sawtooth signal is used as the carrier signal. However, a triangular wave is particularly preferably used as the carrier signal, so that each clock pulse or period has a rising and a falling edge. In particular, the slope of the two edges is the same. If the phase offset is selected to be half the period, the rising edge begins with one of the carrier signals and the falling edge with the other carrier signal. This makes it possible to implement the change in the two useful signals simultaneously. It is also possible to use the inverted other carrier signal as one carrier signal. This reduces hardware requirements. This also allows the phase offset to be set precisely, namely to exactly half the period.

[0034] The method according to the invention is used to commission the system, which has two actuators, each of which is electrically connected to the common DC voltage circuit by means of one of the converters. After commissioning, the system is to be operated according to the method in which a pulse-width modulated signal is generated based on a respective periodic carrier signal, depending on a respective useful signal for the respective actuator. Each converter is operated to apply a corresponding electrical voltage to the respective actuator. The two carrier signals are identical but selected to be offset from each other by a predetermined phase shift.

[0035] The commissioning procedure stipulates that the two carrier signals are initially started at a common time without a phase offset. Consequently, the two carrier signals are initially synchronized with each other. For example, the start-up of the system or another predetermined time is used as the common time. Due to the common time, simultaneous generation and / or synchronization of the carrier signals is simplified. This also makes it possible to check whether the two carrier signals are actually synchronized with each other. If this is not the case, they are restarted, for example, at another common time. Only if this is successful does the commissioning procedure continue.To initiate the carrier signals, a communication system such as a fieldbus is used, through which the converters, particularly their control units, which generate the respective pulse-width modulated signals, are signal-linked. The communication system allows the converters to communicate with each other and / or with a higher-level control unit. In particular, each converter is assigned a specific address for communication purposes.

[0036] InIn a subsequent work step, the frequency of the carrier signal assigned to one of the converters is changed for a period so that the predetermined phase offset results between the carrier signals. This occurs depending on the address of the respective converter, which can be an IP address or another address, for example. The respective address is in particular a number or can be converted into a number, for example. The frequency is preferably changed depending on whether the address is even or odd. If the address is not entirely a number, the distinction is made in particular depending on a digit of the address, in particular the last digit.

[0037] For example, the frequency of the carrier signal assigned to the inverter with an even number or address remains unchanged, whereas the frequencies of the carrier signals assigned to the inverter with an odd number or address are changed for the period. Alternatively, the frequency changes are made for the addresses with an even number or address.

[0038] For example, the frequency is changed for several periods or, more preferably, only for exactly one. After changing the frequency for the period, the frequency of the carrier signal is expediently set back to its original value. In summary, depending on the address of the respective converter, the frequency of the assigned carrier signal is changed for one period and then set back to its original value. The predetermined phase offset results from the change in the frequency for the period, and the frequency is changed in such a way that the predetermined phase offset results. For example, the frequency is changed for several periods / clock cycles, whereby the extent to which the frequency is changed in conjunction with the number of periods leads to the predetermined phase offset, and these are thus adapted to one another.

[0039] Since the respective carrier signal is available to both converters during the frequency change, the pulse-width modulated signal can be generated without the formation of artifacts. Consequently, robustness is increased.

[0040] Particularly preferably, the phase offset is chosen to be equal to half the period, and to modify the frequency, this is expediently set to twice the value, thus reducing the effort. Suitably, the carrier signals have a frequency of 8 kHz, and for one of the carrier signals, the frequency is set to 16 kHz for one period, depending on the address.

[0041] The system comprises two actuators, each electrically connected to a common DC voltage circuit via a converter. The system also includes a (DC) voltage source that supplies the DC voltage circuit. The DC voltage source is, for example, a battery or a rectifier that is electrically connected to a power grid when assembled.

[0042] The system is operated according to a method in which, depending on a respective useful signal for the respective actuator, a pulse-width-modulated signal is generated using a respective periodic carrier signal, and the respective converter is operated to apply a corresponding electrical voltage to the respective actuator. The two carrier signals are selected to be equal but offset from each other by a predetermined phase shift. The system, in particular, has a control unit that is provided and configured to carry out the method. The control unit comprises, for example, an application-specific integrated circuit (ASIC) or, particularly preferably, a computer that is suitably designed to be programmable.In particular, the control unit comprises a storage medium on which a computer program product, also referred to as a computer program, is stored, wherein upon execution of this computer program product, i.e. the program, the computer is caused to carry out the method.

[0043] Particularly preferably, the two converters are connected to each other via signaling, preferably also to any control unit. For example, a communication system, such as a fieldbus, is used for the signaling connection. For example, each converter comprises a control unit, by means of which the respective pulse-width-modulated signal is generated, or by means of which, for example, the electrical voltage is applied depending on the respective pulse-width-modulated signal, for example, generated by the control unit.The control unit is also suitable, provided and configured to carry out a method for commissioning the system, in which the two carrier signals are started at a common time without phase offset, wherein, depending on an address of the respective converter, the frequency of the assigned carrier signal is changed for one period and subsequently reset to the original value, so that the predetermined phase offset results between the carrier signals.

[0044] If the system also has a third actuator and / or converter, the phase offset is, for example, equal to a third of a period or even half of a period, so that two of the carrier signals have no phase offset to each other but do have a phase offset to the remaining carrier signal. Thus, although uncompensated recharging currents occur during operation, these are reduced compared to a completely synchronous carrier signal.

[0045] For example, the individual converters are single-phase, whereby the converters are, for example, a component of a converter complex. In particular, the converter complex is designed as three-phase, and each of the converters supplies current to a phase of an electric motor during operation, for example. Thus, one of the phases of the electric motor is used as the respective actuator. For example, the electric motor is two-phase, or particularly preferably three-phase, so that the converter complex is also designed as three-phase. Expediently, three converters are thus present, which are operated according to the method, whereby two of the carrier signals have no phase offset with respect to one another but have a phase offset with respect to the remaining carrier signal.

[0046] However, it is particularly preferred that the converters are each three-phase and, in particular, comprise a so-called bridge circuit, preferably a B6 circuit. In this case, each converter is preferably assigned the same carrier signal and thus also the same phase offset, so that the individual phases of the same converter are not assigned a phase offset relative to one another. In particular, an electric motor, which is also particularly three-phase, is used as the actuator. For example, in this case, the system is a press, and the two electric motors are expediently used to press two punches together.

[0047] For example, in addition to the electric motor, the respective actuator comprises further components that are powered or operated by the converter. In one alternative, the two actuators are each sub-motors of a common electric motor. The electric motor in particular has a number of phases that corresponds to the number of converters and the phases of the converters. If the converters are three-phase, the electric motor thus comprises six phases, three of which are operated by one converter and the others by the remaining converter. For example, the sub-motors are offset from one another and / or arranged in sections. The stator is preferably formed by the two sub-motors, or the stator comprises at least the sub-motors. Particularly preferably, the electric motor has only a single rotor, which is set in rotation by the two sub-motors.Thanks to the two converters and the two actuators, the maximum force and / or torque that can be generated by the electric motor is increased, allowing the system to generate comparatively high power. Particularly preferred is a phase offset between the two carrier signals equal to half a period, simplifying coordinated operation of the two sub-motors. For example, the same useful signal is used for both actuators.

[0048] The invention also relates to a computer program product comprising a number of instructions which, when the program (computer program product) is executed by a computer, cause the computer to carry out the above-mentioned method for operating the system and / or for commissioning the system. The computer is expediently a component of a control unit or electronics and is formed, for example, by means of the latter. The computer preferably comprises a microprocessor or is formed by means of the latter. The computer program product is, for example, a file or a data carrier containing an executable program which, when installed on a computer, automatically executes the respective method.

[0049] The invention further relates to a storage medium on which the computer program product is stored. Such a storage medium is, for example, a CD-ROM, a DVD, or a Blu-ray disc. Alternatively, the storage medium is a USB stick or other storage device that is, for example, rewritable or only writable once. Such a storage device is, for example, a flash memory, a RAM, or a ROM.

[0050] The invention also relates to a control unit that is provided and configured to carry out the corresponding method. The control unit has, for example, an application-specific integrated circuit (ASIC) and / or a microprocessor, by means of which the respective method is at least partially carried out. In particular, the control unit comprises a computer program product that is stored in a memory and, when the program is executed by a computer, such as the microprocessor, causes the computer to carry out the method.

[0051] The further developments and advantages explained in connection with the method are to be transferred analogously to the system / the computer program product / the storage medium / the control unit as well as to each other and vice versa.

[0052] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings: Fig. 1 schematically shows a system comprising two actuators. Fig. 2 schematically shows a further variant of the system, Fig. 3 a method for commissioning and operation of the system, Fig. 4, 5 the time course of carrier signals during commissioning, and Fig. 6 the time course of useful signals and pulse width modulated signals during operation of the system.

[0053] Corresponding parts are provided with the same reference numerals in all figures.

[0054] In Figure 1A simplified schematic of a system 2 in the form of an electric press is shown. The system 2 has a stationary punch 4 and a movable punch 6 that is movably mounted thereon and guided by a guide 8. This makes it possible to move the movable punch 6 closer to the stationary punch 4 or further away from it. The movable punch 6 is driven by two electric motors 10, each of which represents an actuator 12 of the system 2. Due to the two electric motors 10, the force by which the movable punch 6 can be pressed onto the stationary punch is increased.

[0055] The electric motors 10 are synchronous motors and each have a three-phase design. The electric motors 10 are each powered by an associated converter 14. The converters 14 are three-phase, and each converter 14 has a bridge circuit (not shown in detail), namely a B6 circuit. The converters 14 are powered by a common DC voltage circuit 16, to which a DC voltage of 400 V is applied during operation. In summary, the system 2 thus has two actuators 12, each of which is electrically connected to the common DC voltage circuit 16 by means of one of the converters 14.

[0056] The DC voltage circuit 16 is supplied by a rectifier 18, which serves as a voltage source. The rectifier 18 is electrically connected to a three-phase supply network 20. The system 2 further comprises a control unit 22, which forms a master control unit of a fieldbus 24, so that communication via the fieldbus 24 is coordinated by the control unit 22. The two converters 14 are also signal-connected to the fieldbus 24 and have a suitable control unit for this purpose, which serves as slave control units. Thus, each of the converters 14 is assigned a specific address of the fieldbus 24, such as an IP address.

[0057] In Figure 2A modification of system 2 is shown in detail. Here, only a single electric motor 10 is present, which is also designed as a synchronous motor. However, the electric motor 10 has two sub-motors 26, which form the actuators 12. The sub-motors 26 form the stator 28 of the electric motor 10, with each of the sub-motors 26 forming three of the stator's six phases 30. The phases 30 of the sub-motors 26 are arranged alternately around the circumference, so that the sub-motors 26 are interlaced. The phases 30 of each of the sub-motors 26 are each electrically connected to the same converter 14 and can thus be supplied with current by means of the converter.

[0058] The stator 28 surrounds a common rotor 32, which rotates around a rotation axis 33 when energized by the individual phases 30. In summary, the actuators 12 in this variant are each sub-motors 26 of the common electric motor 10.

[0059] In Figure 3 a method 34 for commissioning the system 2 is shown, which is carried out at least partially by means of the control unit 22 and any control units of the converters 14. In In a first step 36, two carrier signals 40 are started at a common time 38, the temporal course of which is Figure 4is shown. Each of the periodic carrier signals 40 is assigned to one of the converters 14 and has a frequency of 8 kHz. Each carrier signal 40 is generated by the respective control unit after a start signal, which was generated by the control unit 22 and transmitted via the fieldbus 24, has been received at the common time 38. A triangular wave is used as the respective carrier signal 40, which thus has several periods / clocks, each formed by a rising and a falling edge. Due to the start at the common time 38, the two carrier signals 40 are synchronous with one another in time and essentially indistinguishable.

[0060] In In a subsequent second step 42, the frequency of one of the carrier signals 40 is changed for a single period 46 at a further time 44, namely doubled, as in Figure 5This carrier signal 40 thus has a frequency of 16 kHz for period 46. Consequently, this period 46 is already over when only half of the period has elapsed for the other carrier signal 40. In other words, at the next time 44, the frequency of one of the carrier signals 40 is increased. The next time 44 is chosen to be the beginning of one of the clock cycles of the carrier signals 40, which until then each start at the same time.

[0061] The carrier signal 40 that is changed is selected depending on the address of the converter 14. In this example, the carrier signal 40 assigned to the converter 14 with an even address on the fieldbus 24 is arbitrarily changed. If system 2 has more such converters 14, a corresponding carrier signal 40 is also assigned to each of the converters 14. Here, too, regardless of the actual number of converters 14, the frequency for the period 46 is doubled at the further time 44 for each of the carrier signals 40 assigned to one of the converters 14 with an even address.

[0062] In a subsequent third step 48, after the period 46 has elapsed, the modified frequency is reset to its original value, i.e., 8 kHz. As a result, a specific phase shift 50 results between the two carrier signals 40, which is equal to half the period of the unaltered carrier signals 40. In other words, after the third step 48 has been performed, the two carrier signals 40 are again equal, but the predetermined phase shift 50 between them is half a period of the periodic carrier signal 40. Consequently, one of the carrier signals 40 is the inverted of the other carrier signal 40.

[0063] Subsequently, the commissioning procedure 34 is completed, and a procedure 52 for operating system 2 is carried out, also using the control unit 22 and the control units of the converters 14. Consequently, procedure 34 serves to commission system 2, which is to be operated according to procedure 52.

[0064] In a fourth work step 54, two useful signals 56 are received or created by the control unit 22 and transmitted to the two converters 14 via the fieldbus 24. The useful signals 56 correspond to a power requirement, and the same useful signal 56 is used for the two actuators 12. Depending on the useful signal 56, a pulse-width-modulated signal 58 is created for each of the converters 14. For this purpose, the useful signal 56 is compared with the associated carrier signal 40 using a comparator in the respective control unit. If the useful signal 56 is greater than the carrier signal 40, a first value 60 is used as the pulse-width-modulated signal 58. If the useful signal 56 is less than the respective carrier signal 40, a second value 62 is used. Thus, each time the useful signal 56 intersects the associated carrier signal 40, the value of the respective pulse-width modulated signal 58 changes.Since the two useful signals 56 correspond to each other, but the carrier signals 40 are shifted from each other by the phase offset 50, the change between the two values ​​60, 62 in the two pulse-width modulated signals 58 occurs with a temporal shift from each other or in opposite directions.

[0065] Once the pulse-width-modulated signals 58 have been generated, a corresponding electrical voltage is applied to the respective actuator 12 via the respective converter 14. For this purpose, the semiconductor switches of the respective bridge circuit are actuated accordingly. Thus, the shape of the electrical voltage applied to the actuators 12 corresponds to the shape of the respective pulse-width-modulated signal 58, with the first value 60 corresponding to 0 V and the second value 62 corresponding to the electrical DC voltage applied to the DC voltage circuit 16.

[0066] Due to the applied electrical voltage, a current flows through the respective actuator 12. When the applied electrical voltage changes, charge reversal currents occur in each of the actuators 12 due to existing capacitances. However, due to the phase shift 50, the times at which the applied electrical voltage is changed are offset from one another in the two converters 14, or the switching occurs in the exact opposite direction. Therefore, the charge reversal currents in the DC voltage circuit 16 partially or completely cancel each other out. This reduces the load on the rectifier 18 and the feedback to the supply network 20.

[0067] During the control of system 2, the two useful signals 56 are changed simultaneously, provided this is desired or necessary due to the current power requirement. The change always occurs at the beginning of one of the cycles of one of the carrier signals 40 and thus in the middle of one of the cycles of the remaining carrier signal 40. As a result, with the pulse-width-modulated signals 58 changing as a result, none of the actuators 12 is briefly operated with excessively increased or reduced power. In other words, since the two carrier signals 40 are inverted relative to one another, the formation of artifacts is reduced, enabling coordinated operation of the two actuators 12 relative to one another.

[0068] In summary, in method 52, the respective pulse-width-modulated signal 58 is generated based on the respective periodic carrier signal 40 for the respective actuator 12, depending on the respective useful signal 56. The same useful signal 56 is used for the two actuators 12, which are therefore not different. The two carrier signals 40 are triangular waves and identical, but offset from one another by the predetermined phase offset 50, which is selected to be equal to half the period. Each converter 14 is operated to apply the electrical voltage corresponding to the respective pulse-width-modulated signal 58 to the respective actuator 12. List of reference symbols

[0069] 2System 4Fixed punch 6Movable punch 8Guide 10Electric motor 12Actuator 14Converter 16DC circuit 18Rectifier 20Supply network 22Control unit 24Fieldbus 26Partial motor 28Stator 30Phase 32Rotor 33Rotation axis 34Commissioning procedure 36First work step 38Common time 40Carrier signals 42Second work step 44Further time 46Period 48Third work step 50Phase offset 52Operation procedure 54Fourth work step 56Useful signal 58Pulse width modulated signal 60First value 62Second value

Claims

1. Method (34) for commissioning an installation (2), which has two actuators (12) that are electrically contact-connected to a common DC voltage circuit (16) by means of a respective converter (14), and which is intended to be in accordance with a method (52) in which a pulse-width-modulated signal (58) is created on the basis of a respective periodic carrier signal (40) depending on a respective useful signal (56) for the respective actuator (12), and the respective converter (14) is operated so as to apply a corresponding voltage to the respective actuator (12), and in which the two carrier signals (40) are chosen to be identical, but to be offset by a predetermined phase offset (50) in relation to one another, characterized in that - the two carrier signals (40) are started at a shared time (38) without a phase offset, and - depending on an address of the respective converter (14), the frequency of the associated carrier signal (40) is changed for a period (46) and is then set to the original value again so as to produce the predetermined phase offset (50) between the carrier signals (40).

2. Installation (2), which has two actuators (12) electrically contact-connected to a common DC voltage circuit (16) by means of a respective converter (14), and which is put into operation in accordance with a method (34) according to Claim 1.

3. Installation (2) according to Claim 2, characterized in that the converters (14) are three-phase.

4. Installation (2) according to Claim 2 or 3, characterized in that the two actuators (12) are each motor elements (26) of a common electric motor (10).