Drive device for an electric vehicle

0001The invention relates to a drive device for an electric vehicle according to claim 1; Such a drive device is used both in vehicles with sole electric motor drive and in hybrid vehicles with alternating or parallel drive by an electric motor or by an internal combustion engine.

0002In such vehicles operating conditions occur in which the drive is not required by the electric motor power and thus the setpoint input for the motor current is zero; Examples of such idling operation is, for example the so-called push operation of the vehicle without replica of a drag torque or eg the idling of the electric motor in the parallel drive with the internal combustion engine in hybrid vehicles, in which the electric motor is driven by its rigid coupling. It is customary to activate the inverter in such operating conditions and to regulate in the sense of such powered from the battery motor phase currents that the electric motor outputs no torque.

0003Object of the present invention is a range optimization for an electric vehicle with a battery powered electric motor by lower operational load of this battery. The solution of this problem is achieved by a drive device according to claim 1; advantageous embodiments of the invention are the subject of the dependent claims.

0004By the drive device according to the invention can be omitted in an advantageous manner, at least in some areas of idling operation of the electric motor by locking the power switch according to the invention due to the inactivation of the inverter on Endladizastung the battery for the purpose of adjusting a zero torque with appropriate timing of the motor phase currents.

0005The blocking of the circuit breaker in the above conditions is possible in electric vehicles with electric motors with variable field, ie in particular in asynchronous machines or separately excited synchronous machines, advantageously over the entire speed range.

0006When operating an electric vehicle with a particularly advantageous in terms of simple construction synchronous machine with permanent-magnet rotor can also be an uncontrolled, by the drive device according to the invention, possibly leading to damage to the battery leading current flow to the battery can be prevented in the event in that the permanent magnet rotor flux induced terminal voltage of the synchronous machine, especially during operation in the field weakening area, is too high and thus the rectified DC back voltage or DC link voltage at the battery-side output of the inverter exceeds the parallel battery voltage inadmissible. The device according to the invention thus makes it possible, with a particularly low level of circuitry, to achieve range optimization with simultaneous battery protection in the case of a drive device using a permanent-magnet synchronous machine as the electric drive part.

0007For a guaranteed in every case jolt-free acceleration or Braking with appropriate torque input from a previous idle state of the synchronous machine without torque request and with correspondingly disabled circuit breakers reactivation of the circuit breaker is provided with appropriate field-oriented control of the voltage vector for the stator winding of the synchronous machine according to a current setpoint specification and taking into account calculated from the rotor speed and the rotor field position instantaneous machine data ,

0008The invention will be explained in more detail below with reference to a schematically illustrated embodiment.

0009The drawing shows one of a Battere B with the battery voltage U_B and the battery current I_B via a converter U with parallel DC link capacitor C and with six circuit breakers B1-B6 in the usual three-phase bridge circuit fed synchronous machine M with permanent-magnet rotor PM. The permanent-magnet synchronous machine M is connected to its output shaft either alternately or simultaneously rigidly coupled to an internal combustion engine VB or to a vehicle wheel R1 / R2 of an electric vehicle.

0010The following considerations relate in particular to the inventively designed idle operation of the synchronous machine, ie the range in which the setpoint for the torque-generating motor current is zero.

0011The circuit breakers B1-B6 are activated and thus clocked regulated or inactivated disabled via a control unit CB, which is connected via an output stage T with the circuit breakers B1-B6 of the inverter U in control or regulation dependence. The fed from a DC voltage source UV control unit CB via a current measuring device MI, the motor currents I₁; I₂; I₃ the synchronous machine M, via a speed measuring device MR, the actual values ​​of the rotor speed of the synchronous machine M and a voltage measuring device MU at the battery side output of the inverter U voltage applied DC or DC link voltage U_ZW fed.

0012For the automatic determination of the operating point, in which in the inventively considered idling operation of an inactivation of the circuit breaker B1-B6 and thus the battery discharge protection of the battery B on the activation of the power switch B1-B6 and thus the battery overcharge protection is switched, Based on the rotor speed of the synchronous machine M and the known flux actual value of the synchronous machine M, the control unit CB calculates the induced motor terminal voltages U_K12U_K23U_K31 between the winding terminals of the synchronous machine M; this is the inactivation, ie blocking of the circuit breaker B1-B6, rectified by the freewheeling diodes rectified DC voltage or DC link voltage U_ZW, optionally taking into account the voltage drops in the inverter U, determined. If this theoretical intermediate circuit voltage U exceeds_ZW the battery voltage U_B, it could lead to an uncontrolled current flow I_B come from the synchronous machine M to the battery UB and there is a risk of damage to the battery B.

0013Alternatively to the detection of the regenerative DC voltage U_ZW via a separate voltage measuring device MU whose value can also be obtained from an external controller and communicated via a bus system CAN to the control unit CB.

0014By virtue of the activation of the power switches B1-B6 according to the invention, the permanent-magnet synchronous machine M can be impressed with a magnetizing current having such control of the current phase position that the induced terminal voltages U_K12U_K23U_K31 and thus the regenerative DC voltage or DC link voltage U_ZW can be reduced and unwanted recharging the battery B is avoidable. Despite increasing speed and otherwise the battery voltage U_B exceeding DC bus voltage U_ZW is achieved by appropriate control of Magentisierungstromes that no current I_B into the battery B flows and this is not overloaded. The necessary increase in the magnetization current is equivalent to a change in the current phase position, ie the phase position of the motor current relative to the induced terminal voltage of the synchronous machine M. The activation of the circuit breakers B1-B6 takes place simultaneously with specification of a defined phase and amplitude voltage vector, so that balancing operations be avoided in the drive.

0015From the previously defined switching point between the inactivation of the circuit breaker on the one hand and the activation of the circuit breaker on the other hand, the protection of the battery against overload has priority over their protection against discharge; It should be apparent that an optimum between battery protection on the one hand and battery discharge on the other hand by a very wide range of inactivation, ie blocking the circuit breaker, is achieved at high speeds.

0016If the idling mode of the synchronous machine without torque request and with a corresponding inactivated inverter are left and is - eg for the purpose of accelerating from the idle driving state of the electric vehicle - a reactivation provided so are u according to an embodiment of the invention by specifying a corresponding field-oriented controlled voltage vector₁ for the stator winding of the synchronous machine M as a function of their instantaneous rotor speed and their instantaneous position of the rotor field axis unacceptably high currents and thus unwanted torque surges avoidable.

0017The adjustment of the amount | u₁| and the angle γ₁ the voltage vector u₁ expediently takes place by pulse width modulation control of the power switch B1-B6 according to the known room vector modulation via the control unit CB with corresponding control outputs PWM.

0018The voltage to be set on the reactivated power switches B1-B6, to be applied to the machine terminals of the synchronous machine M voltage vector u₁ is in each case defined as a function of a current setpoint value determined, for example, by the position of the accelerator pedal, and the values ​​of the rotor speed .omega. which are respectively instantly detected, eg via a motor-speed sensor MR and a motor-position encoder MP_R and the rotor field angle γ_R,

0019The amount to be applied when reactivating the circuit breakers B1-B6 and u₁ the voltage vector is advantageously determined from a stored model of the synchronous machine M. The amount of voltage is added from the induced voltage of the synchronous machine and the voltage drops at stator resistance and stator inductance. The induced voltage of the machine results from the multiplication of the measured rotor speed ω_R with the rotor flux Ψ_rotor and the pole pair number p. The voltage drop at the stator resistance is calculated by multiplying the stator current setpoint i_1soll and stator resistance R₁, The voltage drop at the stator inductance results from multiplication of stator current setpoint i_1soll, Stator inductance L_σ and electrical rotation frequency ω₁Advantageously, a machine model is used which advantageously determines the stator voltage components in the d-axis (field-forming axis) and in the q-axis (torque-forming axis).<maths id="math0001" num=""><math display="block"><mrow><mtable><mtr><mtd><mrow><mtable><mtr><mtd><mrow><msub><mrow><mtext>u</mtext></mrow><mrow><mtext>1q</mtext></mrow></msub><msub><mrow><mtext> = R</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext> · I</mtext></mrow><mrow><mtext>1q</mtext></mrow></msub><msub><mrow><mtext></mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext> + L</mtext></mrow><mrow><mtext>σ</mtext></mrow></msub><msub><mrow><mtext> · Ω</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext> · I</mtext></mrow><mrow><mtext>1d</mtext></mrow></msub><msub><mrow><mtext></mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext> + ω</mtext></mrow><mrow><mtext>R</mtext></mrow></msub><msub><mrow><mtext> · P · Ψ</mtext></mrow><mrow><mtext>rotor</mtext></mrow></msub></mrow></mtd></mtr><mtr><mtd><mrow><msub><mrow><mtext>u</mtext></mrow><mrow><mtext>1d</mtext></mrow></msub><msub><mrow><mtext> = R</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext> · I</mtext></mrow><mrow><mtext>1d</mtext></mrow></msub><msub><mrow><mtext></mtext></mrow><mrow><mtext>should</mtext></mrow></msub><msub><mrow><mtext> + L</mtext></mrow><mrow><mtext>σ</mtext></mrow></msub><msub><mrow><mtext> · Ω</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext> · I</mtext></mrow><mrow><mtext>1q</mtext></mrow></msub><msub><mrow><mtext></mtext></mrow><mrow><mtext>should</mtext></mrow></msub></mrow></mtd></mtr></mtable></mrow></mtd></mtr></mtable></mrow></math><img file="EP0906847A2_D0001.tif" /></maths>

0020The amount of stator voltage then results from the two previously defined components u_1q or u_1d as follows<maths id="math0002" num=""><math display="block"><mrow><mtext>|</mtext><msub><mrow><mtext mathvariant="italic">u</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><mtext>| =</mtext><msqrt><msubsup><mrow><mtext mathvariant="italic">u</mtext></mrow><mrow><mtext>1</mtext><mtext mathvariant="italic">q</mtext></mrow><mrow><mtext>2</mtext></mrow></msubsup><mtext> + </mtext><msubsup><mrow><mtext mathvariant="italic">u</mtext></mrow><mrow><mtext>1</mtext><mtext mathvariant="italic">d</mtext></mrow><mrow><mtext>2</mtext></mrow></msubsup></msqrt></mrow></math><img file="EP0906847A2_D0002.tif" /></maths>

0021The angle γ to be applied when reactivating the circuit breakers B1-B6₁ The voltage vector is advantageously derived directly from the values ​​of the motor position sensor MP.

0022If the circuit breakers B1-B6 have to be reactivated at a time when, for example, there is no exact angular position due to a lack of resolution of the encoder, then the current angular position must be estimated. For this purpose, the angular position γ_R extrapolated starting from the last encoder information. The extrapolation is performed using the last angular position obtained from the encoder, the time difference to the last encoder information and the current rotor speed. An advantageous embodiment of this extrapolation also incorporates the current rotor acceleration.

0023In the method of the field-oriented control of the synchronous machine now provides the aforementioned determination of the rotor angle γ_R the position of the d-axis (field-forming axis) of the field-oriented coordinate system. The angle of the voltage vector to be set is obtained by referring to the measured position of the γ_R d-axis of the two voltage components u_1d and U_1q spanned angle γ_u added.<maths id="math0003" num=""><math display="block"><mrow><msub><mrow><mtext>γ</mtext></mrow><mrow><mtext>1</mtext></mrow></msub><msub><mrow><mtext> = γ</mtext></mrow><mrow><mtext>R</mtext></mrow></msub><msub><mrow><mtext> + γ</mtext></mrow><mrow><mtext>u</mtext></mrow></msub></mrow></math><img file="EP0906847A2_D0003.tif" /></maths> where γ_u is given by<maths id="math0004" num=""><math display="block"><mrow><msub><mrow><mtext>γ</mtext></mrow><mrow><mtext>u</mtext></mrow></msub><mtext> = arc tan </mtext><mfrac><mrow><msub><mrow><mtext mathvariant="italic">u</mtext></mrow><mrow><mtext mathvariant="italic">d</mtext></mrow></msub></mrow><mrow><msub><mrow><mtext mathvariant="italic">u</mtext></mrow><mrow><mtext mathvariant="italic">q</mtext></mrow></msub></mrow></mfrac></mrow></math><img file="EP0906847A2_D0004.tif" /></maths>