Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
  • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
  • H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using DC to AC converters or inverters
  • H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using DC to AC converters or inverters with pulse width modulation
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P23/00—Arrangements or methods for the control of AC motors characterised by a control method other than vector control
  • H02P23/0004—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
  • H02P23/0027—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control using different modes of control depending on a parameter, e.g. the speed
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
  • H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
  • H02P27/047—V/F converter, wherein the voltage is controlled proportionally with the frequency

Definitions

• the present invention relates to an electric machine, to a control device for controlling said electric machine, to an electric propulsion system comprising said electric machine and said control device, and to a method for controlling said electric machine .
• the present invention relates to an electric machine, which comprises a stator comprising a stator pack made of ferromagnetic material having a circular crown shape in which slots are made, and stator windings partially arranged in the slots, and a rotor.
• Such an electric machine is generally coupled to a control device, in particular an inverter, arranged between the electric machine and a supply source.
• the control device adjusts voltage and frequency at the terminals of the stator windings of the electric machine.
• the torque delivered by the electric machine at a given rpm is a function of the supply voltage and frequency.
• the maximum torque is a function of the frequency and a feature of the electric machine.
• the maximum torque at each frequency further depends on the magnetic stator flux defined by the stator windings.
• the maximum torque is constant in a range of frequencies from zero to a nominal frequency, and quadratically decreases as the frequency of the nominal frequency increases to a maximum frequency.
• a known solution consists in sizing the electric machine so as to increase the maximum torque value at the nominal frequency, because the maximum torque value is thereby also increased at the maximum frequency.
• the electric machine is sized and fed so as to increase the nominal frequency value.
• the maximum torque value at maximum frequency also increases since the maximum torque remains constant in a wider range of frequencies (i.e. to the new nominal frequency) and quadratically decreases in all cases as the frequency increases beyond the new nominal frequency.
• Another object of the present invention is to provide an electric machine which provides a given maximum torque value at the maximum frequency, thus reducing size and/or weight and/or complexity as compared to the prior art.
• Another object of the present invention is to provide an electric machine which has a higher ratio between maximum frequency and nominal frequency than the prior art without increasing size and/or weight and/or complexity as compared to the prior art.
• an electric machine comprising a rotor and a stator which includes a stator pack made of ferromagnetic material and having a plurality of slots and stator windings, for defining a magnetic flux having a maximum magnetic flux value defined on the basis of a first torque value, associated with a nominal frequency; the electric machine being configured to supply a maximum torque equal to a first torque value when fed with a nominal voltage at a frequency lower than or equal to the nominal frequency; the electric machine being configured to supply, in continuous operation, a maximum torque equal to a second torque value when fed with a maximum voltage, higher than the nominal voltage, at the maximum frequency.
• the maximum torque value at the maximum frequency is higher than the prior art, the weight and/or size and/or complexity being equal.
• Another object of the present invention is to provide a control device for controlling an electric machine which reduces the drawbacks of the prior art.
• a control device for controlling an electric machine having a nominal frequency, a nominal voltage, a maximum frequency, and a maximum voltage in continuous operation; the control device being configured to control a frequency and a voltage of the electric machine, in a first frequency range lower than or equal to the nominal frequency, according to a first control mode wherein the variation of the voltage is proportional to the variation of the frequency; and, in a second frequency range higher than the nominal frequency and lower than or equal to the maximum frequency, according to a second control mode wherein the voltage is calculated on the basis of the frequency according to a function; said function defining voltage values higher than the nominal voltage and lower than or equal to the maximum voltage.
• Another object of the present invention is to provide an electric propulsion system which reduces the drawbacks of the prior art.
• an electric propulsion system comprising an electric machine according to any one of the claims 1 to 8, and a control device according to any one of the claims 9 to 14 coupled to the electric machine.
• Another object of the present invention is to provide a control device for controlling an electric machine which obviates the drawbacks of the prior art.
• a method for controlling an electric machine comprising the steps of:
• FIG. 1 is a diagrammatic view, with parts removed for clarity, of an electric propulsion system provided according to the present invention
• figure 2 is a side elevation view, in section and with parts removed for clarity, of an electric machine of the electric propulsion system in figure 1;
• figure 3 is a diagram representing a maximum torque according to the variation of a frequency of the electric machine in figure 2;
• figure 4 is a diagram representing a voltage according to the variation of the frequency of the electric machine in figure 2;
• figure 5 is a diagram representing a magnetic flux according to the variation of the frequency of the electric machine in figure 2.
• reference numeral 1 diagrammatically indicates an electric propulsion system as a whole, in particular a motor vehicle, comprising an asynchronous, multiphase electric machine 2; a control device 3, e.g. an inverter, for controlling electric machine 2; and a rechargeable supply source 4, e.g. a secondary battery, for feeding the electric machine by means of control device 3.
• control device 3 e.g. an inverter
• a rechargeable supply source 4 e.g. a secondary battery
• Supply source 4 supplies a maximum continuous supply voltage V A at its terminals.
• electric machine 2 comprises a stator 6 including a circular crown-shaped stator pack 7 made of ferromagnetic material in which a plurality of slots 8 are made, and stator windings 9 partially arranged in slots 8; and a squirrel cage-like rotor 10 comprising rotor conducting bars 11, two rotor rings 12 (only one rotor ring 12 is shown in figure 2) made of conducting material which short-circuit the conducting bars 11 at the ends and a shaft (not shown in the accompanying figures) for transmitting the rotation outwards from electric machine 2.
• stator 6 including a circular crown-shaped stator pack 7 made of ferromagnetic material in which a plurality of slots 8 are made, and stator windings 9 partially arranged in slots 8; and a squirrel cage-like rotor 10 comprising rotor conducting bars 11, two rotor rings 12 (only one rotor ring 12 is shown in figure 2) made of conducting material which short-circuit the conducting bars 11 at the ends and a shaft (not shown in the accompanying figures) for transmit
• the rotor bars and the two rotor rings are replaced by rotor windings; therefore the rotor is a wound rotor.
• Each stator winding 9 has a terminal (not shown in the accompanying figures) and is associated with a phase of electric machines 2.
• Each stator winding 9 comprises a number N of active, series-connected conductors 15 to define a magnetic flux ⁇ .
• electric machine 2 has a number N of conductors 15 in series per phase which, in turn, define a number of conductors 15 in series per slot 8.
• Electric machine 2 in use, has voltages U and frequency f at the terminals of the stator windings 9.
• Voltages U are the effective voltages concatenated at the terminals of stator windings 9.
• electric machine 2 is characterized by a maximum torque T max , which varies on the basis of the frequency f of the electric machine 2 and, through the shift frequency, is related to a speed SP of rotor 10.
• the maximum torque T max is constant and equal to a first torque value Ti from a zero frequency to a nominal frequency f n , and has values which decrease as the frequency f increases from nominal frequency f n to a maximum frequency f max .
• the first torque value Ti thus represents the maximum value of maximum torque T max of electric machine 2.
• the maximum frequency f max is defined according to a maximum speed value SP max of rotor 10, which is typically established as a specification during the step of designing according to the desired use of electric machine 2.
• the nominal frequency f n is defined as the maximum value of frequency f, so that the maximum torque T max is equal to the first torque value Ti.
• the nominal frequency f n establishes the value of frequency f up to which electric machine 2 exhibits a maximum torque T max equal to the first torque value Ti .
• Both the first torque value ⁇ and the nominal frequency f n are typically established as design specifications according to the desired use of electric machine 2.
• Stator pack 7 comprises foils made of ferromagnetic material, and is structured on the basis of a maximum magnetic flux value ⁇ . Therefore, the structure of stator pack 7 is defined by the first torque value Ti .
• Magnetic flux ⁇ is, inter alia, a function of voltage U, frequency f and number N of conductors 15 in series .
• Electric machine 2 has a nominal voltage U n which corresponds to the value of voltage U to be applied with nominal frequency f n to the electric machine 2, for the maximum torque T max of electric machine 2 to be equal to the first torque value Ti.
• stator 8 is structured to support a maximum voltage U ma x higher than the nominal voltage U n in continuous operation.
• Continuous operation in a condition of use means that the condition of use is compatible with the operation of electric machine 2 over an extended time without the electric machine 2 being damaged due to said condition of use.
• limited operation in a condition of use means the condition of use compatible with the operation of electric machine 2 only over a limited time, beyond which electric machine 2 is damaged as a result of said condition of use.
• the maximum voltage U max is defined according to the supply voltage V A of supply source 4, in particular maximum voltage U max is equal to supply voltage V A .
• the number N of conductors 15 in series is defined on the basis of the maximum voltage U max , the maximum magnetic flux value ⁇ , the nominal frequency f n and the maximum frequency f max .
• the nominal voltage U n is a function of the maximum magnetic flux value ⁇ , the number N of conductors 15 in series, and the nominal frequency f n .
• Electric machine 2 is configured according to the following design requirements :
• the nominal voltage U n and the number N of conductors 15 in series per phase are defined according to the design requirements a) and b) .
• voltage U is set equal to maximum voltage U max , which is equal to voltage V A , frequency f equal to maximum frequency f max and T max equal to the second torque value T 2 .
• the parameterized nominal voltage U n is obtained according to T x , T 2 , f n , f max and V max .
• the nominal voltage U n of electric machine 2 is obtained. Once the nominal voltage U n has been obtained, the number N of conductors 15 in series of electric machine 2 is obtained from the parameterized number N of conductors 15 in series.
• a nominal voltage U n lower than the maximum voltage U max and a number N of conductors 15 in series are chosen during the step of designing, so as to obtain the maximum magnetic flux value ⁇ .
• magnetic flux ⁇ is proportional to voltage U and reversely proportional to the number N of conductors 15 in series.
• the maximum magnetic flux value 4>i also be obtained with nominal voltage U n lower than the maximum voltage U max , providing that a number N of conductors 15 in series lower than that required to have the maximum magnetic flux value ⁇ with the maximum voltage U max is chosen.
• the number N of conductors 15 in series and the nominal voltage U n are defined so that electric machine 2 has a maximum torque T max equal to the second torque value T 2 by applying the maximum voltage U ma x at the maximum frequency f ma x. Furthermore, electric machine 2 has the first torque value Ti when fed with nominal voltage value U n and nominal frequency f n . Requirements a) and b) are met without increasing the size of electric machine 2 through an appropriate scalar control which will be illustrated below.
• Said electric machine 2 may thus be fed in continuous operation with a voltage U higher than the nominal voltage U n , as long as it is not higher than the maximum voltage U ma x # a a frequency f higher than nominal frequency f n and lower than or equal to maximum frequency f max .
• Electric machine 2 comprises a cooling system (not shown in the accompanying figures) sized for a thermal cooling power P t equal to a nominal power P n defined according to the nominal voltage U n at the nominal current consumed at nominal voltage U n and to the efficiency of electric machine 2.
• electric propulsion system 1 comprises a user interface 18 coupled to control device 3 to provide a desired speed SP d , and a speed sensor (not shown in the accompanying figures) coupled to rotor 10 for detecting the rotor speed SP.
• Control device 3 regulates voltage U and frequency f with a scalar control, according to the desired speed SPd and to the detected rotor speed SP.
• scalar control means a control method for an asynchronous electric machine which acts on the effective frequency and voltage at the terminals of the electric machine, and in which the direct component and the quadrature component of the electric magnitude (voltage or current) used for controlling the electric machine 2 are not calculated.
• control device 3 operates according to a first control mode when frequency f is lower than or equal to nominal frequency f n , and according to a second control mode, when frequency f is higher than nominal frequency f n and lower than or equal to the maximum frequency f ma x.
• control device 3 In the first control mode, the variation of voltage U is proportional to the variation of frequency f, as shown in figure 4. In other words, control device 3 proportionally increases the voltage value U to the frequency f itself as frequency f increases. With reference to figures 3 and 5, when control device 3 operates in the first control mode, electric machine 2 has a maximum torque T max equal to the first torque value i and a magnetic flux ⁇ equal to the maximum magnetic flux value ⁇ .
• voltage U is calculated on the basis of frequency f according to a function Ui(f) and takes voltage values U higher than the nominal voltage U n and either lower than or equal to the maximum voltage U max .
• function ui(f) is a curve which joins a point defined by nominal voltage U n and nominal frequency f n to another point defined by maximum voltage U max and maximum frequency fmax.
• the values of voltage U defined by the function ui(f) increase, at least within a range, as frequency f increases. Furthermore, at least in a range, the function ui(f)) has a positive derivative which decreases as frequency f increases .
• the function ui(f) is a rectilinear line which joins the point defined by nominal voltage U n and nominal frequency f n to the point defined by maximum frequency U ma x and maximum frequency f ma x-
• the values of the function ui(f) are defined on the basis of the maximum desired torque values T max and/or on the desired magnetic flux values ⁇ .
• magnetic flux ⁇ from nominal frequency f n to maximum frequency f ma x at least in a range less quickly decreases than a function k/f as the frequency f increases.
• the magnetic flux ⁇ from the nominal frequency f n to the maximum frequency f max has, with the frequency being equal, values higher than a curve A', which is obtained by feeding electric machine 2 with the nominal voltage U n at frequencies higher than the nominal frequency f n .
• the maximum torque T max is proportional to the square of magnetic flux ⁇ , from frequency f n to maximum frequency fmax the maximum torque T max decreases to a lower extent than a quadratic decreases as frequency f increases.
• the maximum torque T max from the nominal frequency to the maximum frequency has, with the frequency being equal, values higher than a curve A' which is obtained by feeding electric machine 2 with the nominal voltage U n at frequencies higher than nominal frequency f n .
• control device 3 is configured to set voltage U equal to the maximum voltage U max only in the surrounding of the maximum frequency f max , and to set the voltage U equal to the nominal voltage U n only in the surrounding of the nominal frequency f n .
• control device 3 defines a scalar control method because it directly regulates voltage U and frequency f at the terminals of electric machine 2 , without calculating the direct component and the quadrature component of the voltage. Therefore, it does not increase the complexity of the control system.
• the present invention is particularly advantageous because it allows to obtain a relatively high ratio between the maximum frequency and the nominal frequency without increasing the size of the electric machine. Furthermore, the described method defines an innovative scalar control which offers better performance than the scalar control of the prior art, without increasing indeed the control complexity. Moreover, the propulsion system provided according to the present invention is relatively light and less cumbersome than the prior art.
• Electric machine 2 is mainly used as an electric motor, and therefore control device 3 feeds electric machine 2 from the supply source 4 as described above.
• the present invention may also be applied when electric machine 2 is used as a generator, and therefore control device 3 recharges supply source 4 by similarly acting as described above.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Ac Motors In General (AREA)
• Control Of Electric Motors In General (AREA)

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• 2010
  • 2010-04-15 IT ITMI2010A000642A patent/IT1402368B1/it active
• 2011
  • 2011-04-15 EP EP11725797A patent/EP2559159A2/de not_active Withdrawn
  • 2011-04-15 WO PCT/IB2011/000839 patent/WO2011128770A2/en not_active Ceased

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