Abstract:
A method for controlling an operation of a multi-phase electric machine with a stator and a rotor is disclosed. The stator or the rotor includes permanent magnets, whereas the rotor or the stator includes a plurality of conductor bars interconnected by connecting elements of at least one circuit board and disposed within a magnetic field of the permanent magnets and having an internal inductance connected. The connecting elements are arranged outside the magnetic field and have an external inductance. Each phase includes at least one of the conductor bars. The multi-phase electric machine is controlled by regulating for each phase of the multi-phase electric machine at least one electrical quantity, which is dependent on the internal and external inductance of a respective phase, to a desired value.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of German Patent Application, Serial No. DE 10 2014 007 632.6, filed May 22, 2014, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a method for controlling an operation of an electric machine, a control system for controlling an operation of an electric machine and an electric machine. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    An electric machine can, in addition to a rotor and a stator, have as components for controlling phases a control gear, which can be configured as an external switching regulator, a rectifier, an inverter and/or a converter, which may in turn include as electronic components metal-oxide-semiconductor field-effect-transistors (MOSFETs) or bridges with bipolar transistors having insulated gate electrodes (IGBT). A pulse-width-modulated (PWM) clock of such an electric machine may have a frequency of about 1 kHz to about 20 kHz. The external switching regulator may be operated at a frequency of about 100 kHz to about 1 MHz. 
         [0005]    It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method, a control system and an electric machine. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the present invention, in a method for controlling an operation of a multi-phase electric machine with a stator and a rotor as components, wherein the stator or the rotor comprises permanent magnets, wherein the rotor or the stator comprises a plurality of conductor bars interconnected by connecting elements of at least one circuit board and disposed within a magnetic field of the permanent magnets and having an internal inductance connected, wherein the connecting elements are arranged outside the magnetic field and have an external inductance, wherein each phase includes at least one of the conductor bars, the electric machine is controlled by regulating for each phase of the multi-phase electric machine at least one electrical quantity, which is dependent on the internal and external inductance of a respective phase, to a desired value. 
         [0007]    According to an advantageous feature of the present invention, the at least one electrical quantity controlled to the intended desired value may be a voltage and/or a current measured for the respective phase. 
         [0008]    According to another advantageous feature of the present invention, an actual instantaneous value of the at least one electrical quantity, i.e. of the voltage and/or the current, of a respective phase may be tapped during operation of the electric machine at a tap disposed between the conductor rods and the connecting elements of the respective phase. 
         [0009]    According to another advantageous feature of the present invention, the desired value of the at least one electrical quantity may be calculated and/or adjusted in dependence of at least one mechanical operating parameters of the electric machine by using an algorithm that is used for the feedforward control of the electric machine. The at least one mechanical operating parameter to be taken into account may be a rotation speed of the electric machine and/or an angular position of the rotor relative to the stator. 
         [0010]    The method can be carried out for an electric machine that is used as an electric motor and/or as a generator. 
         [0011]    According to another aspect of the present invention, a control system is configured to control an operation of an electric machine having as components a stator and a rotor. A first of the two components includes several conductor bars, which are interconnected via connecting elements of at least one circuit board. A second of the two components includes permanent magnets. The conductor bars are arranged within a magnetic field of the permanent magnets and have an internal inductance. The connecting elements are arranged outside the magnetic field and have an external inductance. The electric machine has several phases, with each one of the phases encompassing at least one of the conductor bars. The control system is configured to control for each phase of the electric machine at least one electrical quantity that depends on the internal and external inductance of the respective phase to a desired value. 
         [0012]    Advantageously, the control system for each phase may further include a switching regulator and a control unit which is connected upstream of the switching regulators of all phases. The control unit may be configured to perform an algorithm to be used for feedforward control of the electric machine and to provide the desired value of the at least one electric parameter for the respective phase. 
         [0013]    According to another advantageous feature of the present invention, the control system may include for each phase at least one measurement module configured to measure an actual value of the at least one electrical quantity of the respective phase. 
         [0014]    According to another advantageous feature of the present invention, the control system may include at least one inverter which is disposed between contacts connected to an external voltage source of the electric machine and the phases of the electric motor and is adapted to perform switching control for the electric machine. Furthermore, the control system may include an intermediate circuit capacitor which is arranged between the two contacts. Depending on the definition, the control system may include as further components the phases of the electric machine, wherein each phase has an internal voltage source and an internal resistance associated with the at least one conductor bar of the phase, the internal inductance arranged within a magnetic field of the electric machine, and an external inductance arranged outside the magnetic field of the electric machine. The control system is usually arranged in a housing of the electric machine. 
         [0015]    According to another aspect of the present invention, an electric machine includes as components a stator or a rotor, wherein a first component, usually either the stator or the rotor, includes several conductor bars, which are interconnected via connecting elements of at least one circuit board. A second component, usually the rotor or the stator, includes permanent magnets. The conductor bars are arranged within a magnetic field of the permanent magnets and have an internal inductance. The connecting elements of the at least one printed circuit board are arranged outside the magnetic field and have an external inductance. The electric machine has a number of phases. In one embodiment, each phase has the same number of conductor bars, with each of the phases having at least one of the conductor bars. For controlling an operation of the electric machine, at least one electrical quantity which is dependent on the internal and external inductance of the respective phase for each phase of the electric machine must be controlled to a desired value. 
         [0016]    The electric machine also includes an embodiment of the aforedescribed control system and is to be controlled by an embodiment of the method. The conductor bars of the first component of the electric machine may advantageously be arranged in a soft magnetic material. 
         [0017]    In addition, each phase may include an internal power source, an internal resistance associated with the at least one conductor bar of the respective phase, the internal inductance arranged within a magnetic field of the electric machine, and the external inductance arranged outside the magnetic field of the electric machine. 
         [0018]    The internal and external inductances of the respective phase are to be used for carrying out the switching control during operation of the control system and/or of the electric machine, whereas only the internal inductances of the conductor bars arranged inside the magnetic field are to be used for performing a function of the electric machine. 
         [0019]    Furthermore, the first component of the electric machine may advantageously include iron packets to be produced from iron powder as a soft-magnetic material. These iron packets have grooves in which the conductor rods associated with the phases of the electric machine are arranged. Alternatively, iron laminations made of a soft magnetic material and associated with the conductor bars may be used for the first component. Eddy currents can be reduced and a switching frequency of the electric machine can be increased by using the conductor bars embedded in the iron powder. 
         [0020]    The inverter of the electric machine is at least implicitly used for switching control, which is why the electric machine has for each phase an integrated switching regulator capable of achieving a high switching frequency in the order of 100 kHz to 1 MHz. 
         [0021]    The control system of the electric machine, which has an inverter and the switching regulator, may be integrated in the housing of the electric machine, so that the control system is shielded with regard to electromagnetic compatibility (EMC). The control system may include as electronic switching elements metal-oxide-semiconductor field-effect transistors (MOSFETs) and an intermediate circuit capacitor, for example a ceramic chip capacitor arranged between contacts of the control system to an external voltage source. 
         [0022]    Otherwise conventional coils or windings can thus advantageously be omitted when using the conductor bars for the electric machine. The conductor bars or conductive bars, which replace the windings, are interconnected via connecting elements of the circuit board that may be formed as conductor tracks and/or electronic components. Eddy currents can be minimized by embedding the conductor bars in iron powder as a soft-magnetic composite material (SMC, soft-magnetic composite). 
         [0023]    The equivalent circuit of each phase of the electric machine includes a series circuit with an internal voltage source supplying a voltage with a value that is proportional to the value of the rotational speed of the electric machine, and the internal resistance whose value corresponds to a sum of the values of the resistances of the conductor bars, of the connecting elements, of the MOSFETs and of the equivalent resistance (ESR) of the intermediate circuit capacitor. Furthermore, such a series circuit includes the effective internal inductance of the conductor bars of the respective phase, which are arranged within the magnetic field that causes the Lorentz force of the electric machine. The series circuit further includes the external inductance of the connecting elements, for example conductor tracks, of the phase that are arranged on the at least one printed circuit board outside of the magnetic field. The entire inductance, i.e. the internal and the external inductances, is used in this case for a function of the switching controllers for performing the switching control, whereas only the effective internal inductance is used for the function of the electric machine. In general, the voltage supplied by the external power source must usually be divided by inverters designed as switching regulators and assigned each to a respective phase, wherein the external voltage source is distributed among the internal voltage sources. 
         [0024]    The disclosed control system can perform, inter alia, a function of a switching regulator, with which the voltage of an intermediate circuit of a synchronous converter can be controlled to an actual desired instantaneous value of the voltage of each phase and thus reduced. Accordingly, the current flowing through the respective phase can be regulated to an actually desired value and thus reduced. The control can be performed using conventional switching control methods, pulse methods or so-called chopper methods. A number of the switching regulator hereby corresponds to a number of phases, wherein the switching regulators of the control system are separated from one another. In addition, each switching regulator may include an integrated circuit or a chip. 
         [0025]    An actual value of a voltage and/or an actual value of a current can usually be measured for each phase by using the measurement modules, which are also separated from one another. Furthermore, an output stage and one respective module for controlling the voltage and current may be associated with each phase. In this case, an actual value of the current to be measured can be determined, for example, by way of calculation from one or two measured values of the current flowing through the respective phase. The algorithm to be performed by the control system may also be configured as a feed-forward algorithm. A function of the respective switching controller can be executed quickly, for controlling an AC voltage of a respective phase of the rotating electric machine. 
         [0026]    The electric machine and thus the electric motor and/or generator may have a high switching frequency, so that a current flowing through the conductor bars is no longer constant and thus no longer has a superimposed square-wave pattern. The switching frequency thus does not cause any mechanical excitations. In one embodiment, a currently desired setpoint of the voltage and/or current on the conductor bars is calculated by considering, for example, a field-oriented control of the electric machine. The calculated desired points can be taken into account as default for regulating the voltage and/or the current of the respective phase. 
         [0027]    Optionally, a tap at a physical tapping point disposed between the current and/or voltage between a conductor bar and hence an internal inductance and between a connecting element of the respective circuit board and hence an external inductance can be used. Accordingly, a function for switching control of the electric machine can be separated in the circuitry from an actual function of the electric machine. 
         [0028]    Thus, the inverter and the switching regulator designed, for example, as a step-down switching regulator are combined in the control system of the electric machine, wherein the control system is integrated into the housing of the electric machine. One of the two components of the electric machine, which is designed as a stator or a rotor, has iron packets which are formed from iron powder as a soft magnetic composite material. The conductor bars that replace an otherwise conventional coil of an electric machine favor the intended switching control because a number of otherwise conventional windings of the coils can be reduced by using the conductor bars. It is not necessary to design conductor tracks as connecting elements of the circuit boards commensurate with aspects of switching controls. The conductor bars can also be arranged in iron laminations or transformer sheets to provide a soft magnetic material. The conductor bars are arranged in grooves of the iron packets. The intermediate circuit capacitor disposed between contacts or terminals of the control system to the external voltage source forms hereby a small intermediate circuit. The electric machine can typically be operated in the range of an operating voltage of e.g. 6 volts to 17 volts without sacrificing performance. The rotational speed of the electric machine can be increased by increasing the internal voltage of the electric machine. 
         [0029]    The electric machine can achieve a high switching frequency or clock frequency when carrying out the aforedescribed method. Otherwise conventional wires made of copper and coated with varnish can be eliminated by using the conductor bars. The conductor bars may be made of any electrically conductive material, typically a metal such as iron, aluminum or copper. In addition, the conductor bars have larger diameters than the conventional wires. In each case, a conductor bar is constructed to be either rigid or flexible depending on its thickness and has a polygonal or round cross-sectional shape. Parallel windings and delta connections can be realized by employing the conductor bars. 
         [0030]    In one embodiment, a voltage for supplying this electric machine is increased for increasing an output power of an electric machine, if the machine is operated as an electric motor. An intermediate circuit capacitor of the control system can be implemented as ceramic chip capacitor or a film capacitor, thereby achieving steep flanks with minimal slope moderation in the voltage profile of each phase. In addition, the internal and external inductances of the phases are now used not only for generating a torque of an electric machine described as an electric motor, but are now also used for controlling the operation of electric machine. Thus, both the conductor bars arranged within the soft magnetic material and the connecting elements on the at least one circuit board provided for connecting the conductor bars are used at high clock or switching frequencies for performing a switching regulator function. An internal resistance of the phases of the first component is reduced through use of the conductor bars which have a greater diameter than otherwise used conventional wires. 
         [0031]    The otherwise conventional windings of coils are replaced by the connecting elements on the at least one circuit board that can be produced with thick-film technology. The external inductance of the connecting elements of the at least one phase can also be designed as a so-called planar inductance coil. By using an, for example; ceramic chip capacitor for the small intermediate circuit capacitor, excellent high-frequency characteristics and a low series resistance in comparison with an otherwise conventional electrolytic capacitor with a high capacitance can also be attained. All components of the electric machine and of the control system are typically arranged in a housing of the electric machine and thus shielded from the outside. Furthermore, the electric machine when implemented, for example, as an electric motor, can be operated at a low intermediate circuit voltage. Moreover, the conductor rods are able to conduct high currents compared to otherwise conventional wires. Consequently, the full power of the electric machine can be used across a wide voltage range, in which the electric machine is operated. 
         [0032]    The DC link voltage can be adjusted by controlling the voltage. However, the attainable high currents flow only within the electric machine, but not outside the electric machine. Furthermore, the electric machine can be operated quietly. Moreover, an increased pulse-width-modulated frequency can be achieved by controlled operation of the electric machine according to the method. Usually, high current peaks occur in electric machines, which are designed and/or operated as small, high performance motors, with pulse-width-modulation, which are to be buffered with the provided intermediate circuit capacitor of the electric machine. The capacity of this intermediate circuit capacitor is hereby inversely proportional to this frequency. A ceramic capacitor instead of an electrolytic capacitor is used for the intermediate circuit capacitor. Furthermore, a voltage applied to conductor rods can be reduced without the need to increase the size 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0033]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0034]      FIG. 1  shows a schematic diagram a first embodiment of a control system according to the present invention and a first embodiment of an electric machine according to the present invention; 
           [0035]      FIG. 2  shows a schematic diagram of a second embodiment of a control system according to the present invention; 
           [0036]      FIG. 3  shows a schematic diagram of a detail of a third embodiment of a control system according to the present invention; and 
           [0037]      FIG. 4  shows a schematic diagram of a detail of a fourth embodiment of a control system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0038]    Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0039]    Turning now to the drawing, and in particular to  FIG. 1 , there is shown a first embodiment of the control system  2  according to the invention of the first embodiment of the inventive electric machine  4  which is here entirely arranged in a housing  6  of the electric machine  4 . 
         [0040]    The control system  2  and hence the electric machine  4  are connected by way of contacts  8 ,  9  to an unillustrated external voltage source which supplies a DC voltage Ub. A DC link capacitor  10  as a component of the control system  2  is arranged here between the contact  8  representing the positive pole (+Ub) and the contact  9  representing ground potential. Furthermore, the two contacts  8 ,  9  are connected to an inverter  12  of the control system  2  designed as a half-bridge. This inverter  12  includes here six metal-oxide semiconductor field-effect transistors (MOSFETs) representing electronic switching elements  14 . In the illustrated embodiment of the control system  2  and thus of the electric machine  4 , the inverter  12  is integrated in the housing  6  of the electric machine  4  and is, at the same time, designed as a switching regulator of the electric machine  4 , in this case as a step-down voltage regulator. 
         [0041]    The electronic switching elements  14  of the inverter  12  are here connected to three phases  16 ,  18 ,  20  of the electric machine  4 , wherein each phase  16 ,  18 ,  20  is shown schematically in  FIG. 1  by its equivalent circuit diagram: Each phase  16 ,  18 ,  20  includes here an internal voltage source  22 , wherein a value of a voltage of each of these voltage sources  22  is proportional to a value of a rotational speed of the electric machine  4 . The rotational speed results from a frequency with which a rotor of the electric machine  4  rotates relative to a stator of the electric machine  4 , which are not shown in  FIG. 1 . Each phase  16 ,  18 ,  20  has also an internal resistance  24  that corresponds to a resistance of conductor bars, which form here the phase windings  16 ,  18 ,  20  of the stator as the first component of the electric machine  2 . The conductor bars are arranged in grooves of iron packets of the first component of the electric machine  4 , wherein the first component is embodied here as a stator of the electric machine  4 , wherein the iron packets are to be manufactured from iron powder. Alternatively, i.e. according to another embodiment, the first component could also be designed as the rotor of the electric machine  4 . Furthermore, each phase  16 ,  18 ,  20  includes an internal inductance  26  that corresponds to the inductance of the conductor bars arranged within a magnetic field of the electric machine  4 , and an external inductance  28  arranged outside the magnetic field and corresponding to the inductances of the connecting elements of the at least one circuit board. 
         [0042]      FIG. 2  shows details of the second embodiment of the control system  40 , which is designed to control a second embodiment of an electric machine. The electric machine includes here three phases, wherein an internal voltage source  42  of each phase is shown here. This produces during operation of the electric machine a first voltage U for a first phase, a second voltage V for a second phase, and a third voltage W for a third phase. In addition,  FIG. 2  shows an internal inductance  44  resulting at least for one conductor bar of a phase. An external inductance  46  of each respective phase of the electric machine is produced by connecting elements disposed on at least one circuit board of the electric machine, wherein the conductor bars are electrically interconnected by these electrical connecting elements. 
         [0043]      FIG. 2  shows as components of the control system  40  a control unit  48  and one of a total of three switching regulators  50 , wherein one respective switching regulator  50  is associated with a respective one of the phases. Furthermore, a DC link capacitor  52 , two electronic switching elements  54  as well as a measuring module  56  are associated with each one of the three switching regulators  50 , wherein the measuring module  56  is here configured to measure a current flowing through at least one conductor bar of a respective phase.  FIG. 2  also shows a tap  58  at which a voltage between the internal inductance  44  and the external inductance  46  of the respective phase can be tapped. An actual value of the voltage measured at this tap  58  is transmitted from the tap  58  to the respective switching regulator  50 . 
         [0044]    Furthermore, an actual angle of a rotor of the electric machine relative to a stator of the electric machine and an actual rotational speed of the electric machine are determined as mechanical operating parameters of the electric machine and transmitted to the control unit  48  starting from a node between the voltage sources  42 . Desired values for the voltages U, V, W of the three phases of the electric machine can be determined with the control unit  48  and transmitted to a respective switching regulator  50  by taking into account the actual values of the mechanical operating parameters and of the inductances  44 ,  46  as well as by using an algorithm. 
         [0045]    The switching regulator  50  explicitly shown in  FIG. 2  is here associated with the first phase, for the voltage U of which the determined desired value is to be adjusted. Likewise, a desired value of a voltage V for the second phase is to be transmitted by the control unit  48  to a switching regulator  50  associated with the second phase, and a desired value of a voltage W for a third phase is to be transmitted by the control unit  48  to a third switching regulator  50  associated with the third phase. 
         [0046]    The detail of third embodiment of the control system  70  illustrated in  FIG. 3  includes here an intermediate circuit capacitor  72 , which is arranged here between a contact  74  formed as positive pole and a contact  76  formed as a negative pole of an external voltage source. Furthermore, electronic switching elements  78 , which are each connected downstream of a phase of a plurality of phases of an electric machine to be controlled by the control system  70 , are connected downstream of the intermediate circuit capacitor  72  and the two contacts  74 ,  76 . In addition,  FIG. 3  shows an external inductance  80  of the electric machine and an internal capacitance  82  and an internal resistance  84  of the respective phase of the electric machine. Each phase of the electric machine includes here conductor bars which are interconnected by way of at least one circuit board, in the present example connecting elements arranged on the circuit board. The illustrated external inductance  80  corresponds to the inductance of the connecting elements of the at least one board. The internal capacitance  82  and the internal resistance  84  correspond to the capacitance and the resistance of the conductor bars of the respective phase. The components shown in  FIG. 3  are here also designed as components of a synchronous converter of the control system  70 . 
         [0047]    The detail of the fourth embodiment of the control system  86  schematically illustrated in  FIG. 4  also includes an intermediate circuit resistor  72  and electronic switching elements  78  connected upstream by a respective phase of an electric machine to be controlled by this control system  86 . The electric machine includes here also several, namely three phases. Each phase includes conductor bars which are connected upstream of at least one circuit board of the electric machine by way of connecting elements. In detail,  FIG. 4  also shows three voltage sources  88 , with one of these voltage sources  88  being assigned to a respective phase.  FIG. 4  also shows an internal resistance  90  of the conductor bars of the respective phase, and an internal inductance of the conductor bars  92  of this phase.  FIG. 4  also shows an external inductance  94  of the connecting elements of the at least one circuit board of the respective phase. A tap  96  is arranged between the internal inductance  92  and the external inductance  94 , wherein an actual value of a current flowing through the respective phase and/or an actual value of a voltage of the respective phase can be tapped. 
         [0048]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
         [0049]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: