Abstract:
The invention relates to a circuit arrangement for the selective operation of at least two electric machines ( 1, 2 ) that are each supplied via a plurality of phase lines, comprising:—one voltage protection module ( 5 ) for limiting an intermediate circuit voltage,—one switch arrangement ( 4 ) for selecting one of the electric machines by switching the phase lines;—first choke inductivities ( 8 ) in each of the plurality of phase lines between the circuit arrangement ( 4 ) and the voltage protection module ( 5 ), wherein one second choke inductivity ( 9′ ) each may be switched parallel to one or more first choke inductivities ( 8 ) as a function of the selected electric machine ( 1, 2 ), can be switched.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2008/056456, filed May 27, 2008, which designated the United States and has been published as International Publication No. WO 2008/145647 and which claims the priorities of German Patent Applications, Serial No. 10 2007 025 256.2, filed May 30, 2007, and 10 2008 008 046.2, filed Feb. 8, 2008, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a circuit arrangement for the operation of at least two electric machines with a different inductance requirement being placed on a converter power section. 
     In the machine tool industry, specifically in machining centers, there is increasingly the need to operate at least two spindles with the corresponding drives using one power section. In this case, different spindles, which are each driven by an electric machine, are used for machining, for example roughturning and fine machining/planing. The replacement of the spindles generally takes place via a tool robot. In this case, the two spindles driven by synchronous motors are intended to be operated in an inexpensive manner using one power section. 
     The electric machines are often in the form of synchronous motors. Owing to the need to operate the electric machines at a certain power in the field weakening range, a choke inductance is required as a series inductor (series inductance), which needs to be matched to the inductance of the respective electric machine. Inexpensive circuitry for the choke inductances and the electric machines for both operating cases is therefore desired. 
     In the event of failure of the power section/actuating drive (pulse suppression) in the case of a maximum speed of the electric machine, said electric machine acts as a generator. In this case, a generator voltage (EMF) of up to several kV can be produced, which can damage or destroy other components in the drive circuit. A voltage protection module VPM limits this voltage, for example to a maximum of 830 V, by virtue of the fact that the three phase lines are short-circuited in the corresponding case. The circuit for driving the electric machines including the associated choke inductances therefore needs to be selected in such a way that the generator voltage is safely limited even in the event of a voltage failure. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide advantageous circuitry for the abovementioned components, wherein it is intended for the number of components required to be reduced to a minimum and the function of the voltage protection module for the operation of both electric machines continues to be ensured. 
     According to one aspect of the invention, the object is achieved by a circuit arrangement for the selective operation of at least two electric machines, which are each supplied via a plurality of phase lines, including a voltage protection module for limiting an intermediate circuit voltage, a switch arrangement for selecting one of the electric machines by switching over the phase lines; first choke inductances in each of the plurality of phase lines between the switch arrangement and the voltage protection module, wherein in each phase line a second choke inductance can be connected in parallel with one or more corresponding first choke inductances, depending on the selected electric machine. 
     According to another aspect of the invention, the object is achieved by a drive system which includes a circuit arrangement, as set forth above, and a plurality of electric machines. 
     According to yet another aspect of the invention, the object is achieved by a method for the operation of at least two electric machines which are each supplied via a plurality of phase lines, a voltage protection module being provided for limiting an intermediate circuit voltage, and one of the electric machines being selected by switching over the phase lines by means of a switching arrangement, with one second choke inductance being switchably connected in parallel with one or more first choke inductances, which are arranged in each of the plurality of phase lines between the switch arrangement and the voltage protection module, depending on the selected electric machine. 
     Further advantageous refinements of the invention are specified in the dependent claims. 
     One aspect provides a circuit arrangement for the selective operation of at least two electric machines, which are each supplied via a plurality of phase lines, comprising:
         a voltage protection module for limiting an intermediate circuit voltage,   a switch arrangement for selecting one of the electric machines by switching over the phase lines;   first choke inductances in each of the plurality of phase lines between the switch arrangement and the voltage protection module,
 
wherein in each case a second choke inductance can be connected in parallel with one or a plurality of the first choke inductances, depending on the electric machine selected.
       

     The circuit arrangement advantageously makes it possible to reduce the number of components required for operation of two electric machines using one power section. 
     Furthermore, the voltage protection module may be designed to short-circuit the phase lines depending on an intermediate circuit voltage. 
     In accordance with one embodiment, the second choke inductance can be connectable into the circuit by a contactor depending on a switching signal, the switching signal being provided for driving the switch arrangement. 
     In accordance with a further aspect, a drive system with the above circuit arrangement and with a plurality of electric machines is provided. 
     In this case, the first choke inductances can be designed in such a way that a first of the electric machines can be operated in the field weakening mode of operation, and the second choke inductances can be designed in such a way that a second of the electric machines can be operated in the field weakening mode of operation when the first and second choke inductances are connected in parallel in at least one of the phase lines, the second choke inductances not being connected into the circuit when the first electric machine is selected, and the second choke inductances being connected into the circuit when the second electric machine is selected. 
     A further aspect provides a method for the selective operation of at least two electric machines, which are each supplied via a plurality of phase lines, a voltage protection module being provided for limiting an intermediate circuit voltage, and one of the electric machines being selected by switching over the phase lines, in each case one second choke inductance being in parallel with one or more first choke inductances, which are arranged in each of the plurality of phase lines between the switch arrangement and the voltage protection module, depending on the electric machine selected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Preferred embodiments of the invention will be explained in more detail below with reference to the attached drawings, in which: 
         FIG. 1  shows a schematic illustration of a drive system with two selectable motors; 
         FIG. 2  shows a schematic illustration of a drive system with two selectable motors in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a schematic of a basic circuit  100  for operating two motors  1 ,  2  using one power section  3 . One of the motors  1 ,  2  is selected by a selector switch  4 . The power section  3  is connected to the motors  1 ,  2  via a voltage protection module (VPM)  5  with a first changeover switch  6  and a second changeover switch  7 . The changeover switches are in the form of contactors. A first choke inductance and a second choke inductance  8 ,  9  for each phase line are located between the first changeover switch  6  and the second changeover switch  7 , the changeover switches  6 ,  7  being operated in such a way that either the first choke inductances  8  or the second choke inductances  9  are connected into the phase lines between the voltage protection module  5  and the respective motor  1 ,  2 . 
     The voltage protection module  5  is a safety module and ensures that no voltages which are higher than 830 V can arise in the convertor intermediate circuit, and thus the voltage protection module VPM primarily contributes to the converter protection, and also ensures that the spindle is decelerated in a defined time. This is achieved by short-circuiting of the three phase lines. 
     The circuit shown in  FIG. 1  furthermore has the following features: 
     The motors correspond, for example, to spindle motors and are designed using synchronous technology, i.e. permanent magnets are located in the rotor which cause the excitation of the motor. 
     Owing to the need to operate the motors at a specific power in the field weakening range, the series-connected choke inductances are required which each need to be matched to the inductance of the respective motor  1 ,  2 . 
     In the worst case scenario, such as in the event of failure of the power section/actuating drive (pulse suppression), for example, at the maximum speed of the motor, the motor acts as a generator. In this case, an EMF of up to 2 kV can result. The voltage protection module  5  limits this voltage to a maximum of 830 V by virtue of the fact that the three phase lines (power lines) are short-circuited. 
     The circuit/arrangement of the components (contactors, VPM) needs to be selected in such a way that, even in the event of a voltage failure, the EMF on the phase lines is safely limited. 
     The requirements as regards the circuitry of the components used will be explained below: 
     Two motors (spindles) with different parameters in the field weakening range with different choke inductances (series inductors)  8 ,  9  are operated using one power section  3 . In this case, only one motor  1 ,  2  is ever in operation. 
     Owing to costs, if possible only one voltage protection module  5  is intended to be used. 
     Two choke inductances per phase line are required in order to be able to safely operate the two motors in the field weakening range. 
     Corresponding circuitry between the changeover switches  6 ,  7  and the choke inductances  8 ,  9  needs to produce the connection to the motor  1 ,  2 . 
     The intention is preferably to ensure that, in the event of a voltage failure, the voltage protection module  5  remains connected to the motor (spindle)  1 ,  2  in order to ensure that the EMF is limited to 830 V. This is not achieved in the proposal above in  FIG. 1  since the changeover switches  6 ,  7  in the form of contactors release in the event of a fault. In addition, the high voltage peaks would damage the contacts of the contactors. Thus, limitation of the EMF and safe deceleration of the corresponding motor  1 ,  2  would not be ensured in the event of a fault. 
       FIG. 2  shows an embodiment of the present invention. Identical reference symbols correspond to components of identical or comparable function. 
     The circuit arrangement  101  of the interconnected components was selected in such a way that the worst case scenario of failure of the power section  3  is managed safely both during operation of the motor  1  and during operation of the motor  2 , and thus no unsafe states can occur. 
     In the embodiment shown in  FIG. 2 , the voltage protection module  5  is connected to the power section  3  via three phase lines. The voltage protection module  5  is connected to a motor arrangement with a plurality of motors  1 ,  2  via three phase lines. The motor arrangement comprises the motors  1 ,  2  to be driven by the common power section  3 , it being possible for the motors to be operated only individually using the power section  3 . For this purpose, the motor arrangement has a changeover switch  4 , which, corresponding to an input variable, selects the respective motor  1 ,  2  and connects said motor to the phase lines of the voltage protection module  5 . 
     In each case one first choke inductance  8  is located in the phase lines between the voltage protection module  5  and the changeover switch  4 . 
     Second choke inductances  9 ′ can be connected in parallel with each of the first choke inductances  8  via a respective switch  10 . The switch  10  is operated depending on the operation of the changeover switch  4  and is preferably driven by the same signal. 
     The worst case scenario can arise, for example, when one of the motors  1 ,  2  runs at maximum speed and, precisely at this point in time, the converter located in the power section  3  fails owing to a system voltage failure or another fault on account of pulse suppression. 
     Choke inductances  8 ,  9 ′ are required for operating the motor at a specific power in the field weakening range. The inductance of the corresponding choke inductances  8 ,  9 ′ is dependent on the power of the motor  1 ,  2  to be operated thereby, the field weakening mode of operation run and the maximum achievable speed of the motor. 
     One advantage of the circuit arrangement shown in  FIG. 2  consists in the fact that the circuitry of the components has been selected in such a way that the requirements (EMF limitation in the worst case scenario) are safely met. This is achieved by the always continuous and inseparable connection between the voltage protection module  5 , the first choke inductances  8  and the motor  1 ,  2  selected at that time. This is also ensured in particular when the switch  10  in the form of a contactor, for example, changes its switching position, for example as a result of a voltage failure. 
     The circuit also has the advantage that an additional contactor is not required between the voltage protection module  5  and the choke inductances  8 ,  9 ′, as a result of which the total number of components can be reduced. 
     The switch  10  is only switched on when the motor  2  is used. Thus, the required total inductance for motor  2  is produced via the connected inductor  9 ′, with the inductance of the parallel circuit comprising the inductance  8  and the inductance  9 ′ being produced as the total inductance in each phase line. 
     If the above-described worst case scenario now occurs, the motor current can always flow via the choke inductance  8  via the voltage protection module  5  and the EMF of the motor  2  is thus safely limited. 
     The number of phase lines in the above-described embodiments is assumed to be three, but it is also possible for the number of phase lines to be greater than or less than three. Furthermore, any desired number of motors can be provided instead of only two motors, with these motors being individually selectable. Either no second choke inductances or the second choke inductances  9 ′ which are associated with the respective motor are connected in parallel with the first choke inductances  8 , depending on the motor selected.