Abstract:
A device for monitoring a measuring system of an electric drive is described, including a measuring system ( 12 ) for detecting at least one measured quantity of an electric drive ( 10 ), at least one controller ( 78 ) which receives at least the measured quantity detected by the measuring system ( 12 ) and generates at least one manipulated variable for controlling the drive ( 10 ), where at least one signal acquisition ( 34, 73, 79, 89, 91, 93 ) is provided for detecting errors in the measuring system ( 12 ).

Description:
BACKGROUND INFORMATION 
     The present invention relates to a device for monitoring a measuring system of an electric drive according to the definition of the species of the independent claim. German Patent 43 30 823 C2 describes a drive device having a safety device for special operation. In a special mode, a redundant safety device monitors the rotation speed of the motor to determine whether it is maintaining a preset maximum, interrupting the power supply to the motor when the rotation speed exceeds the preset maximum. To determine the rotation speed, two different signals are obtained, the first signal being obtained from a rotation speed sensor and the second signal being derived from the variation over time of the current measured by another sensor for this purpose in at least one phase lead to the motor. If the rotation speed detected exceeds a predetermined maximum, the power supply to the motor is interrupted by switching a circuit breaker upstream from a line rectifier and also disconnecting the power inverter. Monitoring a speed sensor on the basis of the current variation is load-dependent and therefore relatively inaccurate. The object of the present invention is to provide an improved monitoring system over the entire rotation speed range without requiring an additional rotation speed sensor. 
     ADVANTAGES OF THE INVENTION 
     The device according to the present invention for monitoring a measuring system of an electric drive includes at least one measuring system for detecting a measured quantity of an electric drive and at least one controller which receives at least the measured quantity detected by the measuring system and generates at least one manipulated variable to control the drive. At least one signal processor is provided for detection of errors in the measuring system. This yields early detection of errors in the drive system if there is an error in the measuring system. 
     In an expedient refinement, at least one quantity generated by the controller is sent to the signal processor for error detection in the measuring system. No additional signal acquisition is necessary for error detection due to a skillful choice of the controller quantity for analysis. Since the controller is available with the drive system anyway, the system&#39;s interference immunity can be improved by simple means. 
     In an expedient embodiment, the signal processor receives at least one quantity generated by the measuring system and/or derived therefrom for error detection in the measuring system. Including an additional quantity for analysis increases reliability in error detection. If multiple error detection options are provided in particular, analysis of the quantity supplied by the measuring system can be used for checking the plausibility of the error detection. 
     In another expedient embodiment, a measuring system model that generates at least one estimate expected for the measuring system is provided for error detection in the measuring system. Taking into account the estimate of the measuring system model further increases the reliability of the error detection and can also be used for a plausibility check. 
     A device according to the present invention for monitoring a measuring system of an electric drive is characterized in that a signal processor generates an error signal, as a function of the synchronous generated voltage, thus indicating an error in the measuring system. The synchronous generated voltage varies when the measuring system of the electric drive, e.g., a rotation speed sensor or a position sensor, slips and therefore there is a sensor offset. In particular, the flux-forming component of the synchronous generated voltage is suitable as a quantity for analysis. The sensor offset with respect to the rotor in comparison with the normal case changes the voltage induced in the field direction and is also available during ongoing operation of the electric drive. Countermeasures can be taken in due time if a faulty sensor arrangement is detected. 
     In an expedient embodiment, an output quantity of a direct-axis current controller is used to generate an error signal. Usually, to regulate a synchronous or asynchronous machine, a direct-axis current controller is usually provided for regulation of the flux-forming current component. Because of the additional (direct-axis) voltage component induced due to the sensor offset, a system deviation also develops with a direct-axis current controller. 
     Therefore, the integral component of the direct-axis current controller can be analyzed as a quantity indicating sensor offset in a measuring system, because the integral component is a measure of the additional direct-axis voltage induced due to the sensor offset. This quantity is available at the controller anyway and need not be generated separately. 
     An advantageous embodiment provides for the quantity indicating sensor offset to be compared with a limit value which depends on the controller parameters and/or the line parameters. System deviations may be caused in particular by the dead time voltage due to the switch dead time of the trigger stage, the induced synchronous generated voltage due to the dead time of the quadrature-axis current controller or parameter deviations in inductors and resistors, additionally affecting the integral component of the direct-axis current controller. Since the controller parameters and line parameters are approximately known, they can be taken into account in selecting the limit value with which the integral component of the direct-axis current controller is compared. This increases accuracy in error detection in the measuring system. 
     An alternative embodiment is characterized in that the acceleration of the drive derived from the output signal of the measuring system is analyzed. In the subsequent comparison with certain limit values, any lack of mechanical connection between the electric drive and the sensor is detected. In an expedient refinement, this monitoring is active only when the setpoint current preset by the drive controller reaches the maximum allowed setpoint current. In this case, a critical operating situation may be assumed, possibly caused by a defective measuring system. This embodiment is preferably carried out as a plausibility check in parallel with other sensor monitoring methods. 
     In an alternative embodiment, a rotation speed monitoring model is provided for monitoring a measuring system of an electric drive, generating an estimate of the output signal of the measuring system as a function of certain input quantities. If there arc significant deviations with respect to the actual output signal of that measuring system, a defective measuring system is inferred. 
     In an expedient embodiment, a selector module is provided to select the monitoring function as a function of the estimated rotation speed. The rotation speed monitoring model is used at high rotation speeds. Since this is ineffective at low rotation speeds, direct-axis voltage monitoring is relied on for this case. This ensures that an error in the measuring system will be detected reliably in any rotation speed range. 
     Additional expedient embodiments are derived from additional dependent claims and from the description. 
    
    
     DRAWING 
     The embodiments of the present invention are illustrated in the drawing and are described in greater detail below. 
     FIG. 1 shows a controller structure having a monitoring device of a synchronous machine; 
     FIG. 2 shows a controller structure having, a monitoring device of an asynchronous machine: 
     FIG. 3 shows a block diagram of direct-axis voltage monitoring: 
     FIG. 4 shows a control engineering equivalent circuit diagram of the synchronous machine in the normal case: 
     FIG. 5 shows a control engineering equivalent circuit diagram of the synchronous machine in the case of an error: 
     FIG. 6 shows a block diagram of the monitoring device for the asynchronous machine, and 
     FIG. 7 shows a rotation speed monitoring model. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     A rotation speed-position sensor  12  as a measuring system detects the angular displacement of an electric drive  10 , namely a synchronous machine in the first embodiment according to FIG. 1. A converter  14  driven by a pulse width modulator  16  supplies with current the three phases of electric drive  10 . Current sensors  20  whose output signals  11 ,  13  arc sent to an input transformer  22  are provided in taco of the three phases. Input transformer  22  generates a quadrature-axis current actual value IQ_IST and a direct-axis current actual value ID_IST. Quantity ω from which a direction angle φ is formed by an integrator  26  is obtained over a first differentiator  30  to which the angular displacement is sent. A sine-cosine generator  28  supplies corresponding sin(φ) and cos(φ) values to input transformer  22  and output transformer  18  from direction angle φ. By way of a converter  31 , a sensor rotation speed actual value n_sensor is formed from the output quantity of first differentiator  30  and sent (with a negative sign) to a second differentiator  32  and a second summation point  42 . The output signal of second differentiator  32  functions as an input quantity for a circuit component labeled as a plausibility check  34 . Plausibility check  34  generates a plausibility error signal  35 . A speed controller  44  forms a quadrature-axis current setpoint value IQ_SOLL from the rotation speed deviation available at second summation point  42  between rotation speed setpoint n_soll and a sensor rotation speed actual value n_sensor and sends it to a third summation point  46 , plausibility check  34  and a buffer  50 . Quadrature-axis current actual value IQ_IST formed by input transformer  22  is used as an input quantity for plausibility check  34  and (with a negative sign) for third summation point  46 . The system deviation of quadrature-axis current setpoint value IQ_SOLL and quadrature-axis current actual value IQ_IST is sent to a quadrature-axis current controller  48  designed as a PI controller. The system deviation of direct-axis current setpoint ID_SOLL and direct-axis current actual value ID_IST, generated by input transformer  22  is available at a fourth summation point  52  as an input quantity for a direct-axis current controller  54 , also designed as a PI controller. Direct-axis current setpoint ID_SOLL assumes a value of zero for the synchronous machine. It is also sent to buffer  50 . At a fifth summation point  56 , an output quantity of buffer  50  is subtracted from the output signal of quadrature-axis current controller  48 , yielding a quadrature-axis voltage setpoint value UQ_SOLL. Similarly, a direct-axis voltage setpoint UD_SOLL is generated at a sixth summation point  58 . Quadrature-axis voltage setpoint UQ_SOLL and direct-axis voltage setpoint UD_SOLL form input quantities for output transformer  18 . Output transformer  18  converts these values together with sin(φ) and cos(φ) into two additional voltage setpoints US 1 _SOLL, US 2 _SOLL which are sent to pulse width modulator  16 . 
     The block diagram according to FIG. 2 shows the controller structure of an asynchronous machine. It is essentially identical to the controller structure of the synchronous machine shown in FIG. 1 except that direct-axis current setpoint ID_SOLL is no longer set at a value of zero, but instead an output quantity of a voltage controller  85 . Voltage controller  85  receives as input quantities quantrature-axis current setpoint value IQ_SOLL, quadrature-axis voltage setpoint UQ_SOLL and direct-axis voltage setpoint UD_SOLL. Integral component I_ANTEIL_D of direct-axis current controller  54  is sent to a direct-axis voltage controller  87  whose output quantity is used at summation point  25  as an input quantity in addition to slip ω·s and the output quantity of flux model  24 . 
     The embodiment according to FIGS. 1 and 2 is expanded and made more precise in FIG.  3 . Quadrature-axis current controller  48  can be represented by a parallel circuit of a proportioned component  60  and an integral component  61  of quadrature-axis current controller  48 . Direct-axis current controller  54  is composed of a parallel-connected proportional component  63  and an integral component  64 . The output of integrator  64  of direct-axis current controller  54  is sent to a comparator  73  which receives a limit value (i and generates a direct-axis voltage error signal  75 . Multiplying angular velocity ω (angular velocity of the d-q coordinate system) by interlinked flux Ψp yields a synchronous generated voltage Up, which is sent to fifth summation point  56 . Buffer  50  is implemented by a first proportional element  69  (stator resistor R S ), a second proportional element  70  (stator inductor L S ) and a third proportional element  71  (stator resistor R S ) and two multipliers  66 ,  67 . 
     In the case of the control engineering equivalent circuit diagram of the synchronous machine in the normal case according to FIG. 4, a direct-axis voltage Ud of the drive is sent to a tenth summation point  110 . From the output quantity of tenth summation point  110 , a PT1 direct-axis component  115  forms a direct-axis current Isd of the drive which is used by a third multiplier  113  as an input quantity in addition to angular veloeity ω (angular velocity of the d-q coordinate system). The output quantity of third multiplier  113  weighted with stator inductance L S  is used, in addition to a quadrature-axis voltage Uq of the drive and a negative synchronous generated voltage Up (formed from the product of angular velocity ω and a magnetic flux Ψ p ) with a negative sign as an input quantity by an eleventh summation point  111 . A PT1 quadrature-axis component  116  determines a quadrature-axis current Isq of the drive from the output quantity of eleventh summation point  111 . A proportionality factor  118  ( 3 / 2 ·P·Ψ p ) which takes into account the number of pole pairs p and magnetic flux Ψ p  forms from this an electric moment Mel from which a load moment Mi is subtracted in a twelfth summation point  112 . The resulting quantity is processed by an integrator  119 , weighted with a reciprocal of the mass inertia moment J to yield angular velocity ωm of the rotor. If angular velocity ωm of the rotor is multiplied by the number of pole pairs p (reference number  120 ). this yields angular velocity ω (angular velocity of the d-q coordinate system), which is sent as a second input quantity to two multipliers  113 ,  114 . The output quantity of a fourth multiplier  114  weighted with stator inductance L S  is used as an input quantity by tenth summation point  110 . 
     The control engineering equivalent circuit diagram of the synchronous machine in the event of an error according to FIG. 5 differs from the normal case illustrated in FIG. 4 as follows. Now only synchronous generated voltage Up (Up=ω·Ψ p ) weighted with a factor cos(α)  117 ′ is returned as a negative value to eleventh summation point  111 , where α is the offset angle of rotation speed-position sensor  12 , with respect to its original arrangement in error-free operation. Due to sensor offset α, synchronous generated voltage Up weighted with a factor sin(α)  121 ′ also goes to tenth summation point  110 . The effects of sensor offset α are also reflected in proportionality factor  118 ′ with factor cos(α). 
     FIG. 6 shows the monitoring concept of the asynchronous machine. Direct-axis voltage monitor  79  shown in FIG. 3 is integrated into controller  78  according to FIG.  2 . In addition, a rotation speed monitoring model  89  is provided as a measuring system model which receives quadrature-axis voltage and quadrature-axis current setpoints UQ_SOLL, IQ_SOLL, direct-axis current actual value ID_IST and the flux actual value. As an output quantity, rotation speed monitoring model  89  supplies estimated rotation speed n_modell to a comparator  91  and a reversing switch  93 . Reversing switch  93  receives a model error signal  92  as an output signal of comparator  91  and direct-axis voltage error signal  75  as the output quantity of comparator  73  of direct-axis voltage monitor  79  according to FIG.  3 . 
     FIG. 7 shows rotation speed monitoring model  89  in greater detail. Quadrature-axis current setpoint value IQ_SOLL, weighted using a proportional element “rotor resistor”  96 , goes to a first divider  99  and over a proportional element “stator resistor”  95  with a negative sign to a seventh summation point  102 . Seventh summation point  102  also receives quadrature-axis voltage setpoint UQ_SOLL as an input quantity and supplies the resulting output quantity to an eighth summation point  103 . The actual flux value is sent to a first divider  99  and a second divider  100 . The output quantity of first divider  99  is sent to a ninth summation point  104 . Second divider  100  receives as an additional input quantity the output quantity of eighth summation point  103  and supplies its output quantity to ninth summation point  104  (with a negative sign) and (weighted with a proportional element “leakage inductance”  97  ) to a multiplier  105 . As an additional input quantity, multiplier  105  receives quadrature-axis current actual value IQ_IST and delivers the resulting output quantity with a negative sign to eighth summation point  103 . An integrator  107  processes the output quantity of ninth summation point  104  to yield an estimated rotation speed n_modell. 
     According to the theory of field-oriented control of a synchronous or asynchronous machine, stator current  11 ,  13  detected by current sensors  20  can be divided into two components, namely quadrature-axis current actual value IQ_IST and direct-axis current actual value ID_IST, after conversion to a rotor-based orthogonal two-phase system (d-q coordinate system). Direct-axis current component ID builds up the magnetic field of the machine and is oriented in the same direction as the field. Quadrature-axis current IQ is perpendicular to direct-axis current ID and together with it forms the resultant current which rotates with rotational frequency ω of the field. Quadrature-axis current IQ_IST forms the torque of electric drive  10 , while direct-axis voltage ID_IST is the flux-forming current component. 
     Plausibility check  34  described below monitors the rotation speed control circuit for plausible acceleration data when quadrature-axis current setpoint value IQ_SOLL reaches maximum current I max  which can still be output by speed controller  44 . The drive system receives a maximum torque. By differentiating the output signal of rotation speed-position sensor  12  twice, actual acceleration a_ist is obtained. An error signal is generated if actual acceleration a_ist is less than a preselectable minimum acceleration. Electric drive  10  could he in a blocked state. A corresponding display with the error message “blocked” may be provided. An error message is also generated if actual acceleration a_ist does not have the same sign as quadrature-axis current setpoint IQ_SOLL. In this case, rotation speed-position sensor  12  might be twisted or the motor leads might be connected incorrectly. An interruption in power supply to drive  10  can be detected on the basis of quadrature-axis current actual value IQ_IST if no quadrature-axis current actual value IQ_IST can be determined despite a maximum allowed quadrature-axis current setpoint value IQ_SOLL. Plausibility check  34  is used in particular for rapid response to an incorrectly adjusted rotation speed-position sensor  12  or to lack of mechanical coupling between rotation speed-position sensor  12  and drive  10 . 
     Subsequent direct-axis voltage monitoring  79  according to FIG. 3 is used in particular to determine a slipping rotation speed-position sensor  12 . A slipping rotation speed-position sensor  12  indicates a rotation speed deviating from the actual rotation speed of drive  10 . For the synchronous machine, rotation speed-position sensor  12  is normally set to drive  10  so that the rotor and the stator resistance axis of phase U are in opposition at a measured angular displacement of 0°. A loose screw joint of rotation speed-position sensor  12  causes the rotor position to no longer correspond to the imaginary longitudinal axis of the current controller. 
     In this case, the coordinate system of the current controller based on the rotor is twisted toward the rotor by sensor offset α. For further calculation, it is assumed for the sake of simplicity that sensor offset α relative to angular displacement ε hardly changes at all (α=const). 
     Coordinate System Based on the Stator              Normal                 case           Error                 case               α   =   ∅             α                 constant     ≠   ∅                   Ψ   _     P     =       Ψ   P     *     e     j                 ɛ                     Ψ   _     P     =       Ψ   P     *     e     j        (     ɛ   +   α     )                       (   1.1   )           (   1.2   )                   U   _     P     =     j                   Ψ   P     *     e     j                 ɛ       *          ɛ          t                     U   _     P     =     j                   Ψ   p     *     e     j                 ɛ       *          ɛ          t                                      
     Coordinate System Based on the Rotor              Normal                 case           Error                 case                     U   ′     _     P     =       U   P     *     e       -   j                   ɛ                       U   ′     _     P     =       U   P     *     e     -     j        (     ɛ   +   α     )                               U   ′     _     P     =     j                   Ψ   P     *     e     j                 ɛ       *          ɛ          t                       U   ′     _     P     =     j                   Ψ   P     *     e     j                   (     ɛ   +   α     )         *          ɛ          t                     (   1.3   )           (   1.4   )                     U   ′     _     P     =     j                   U   P                     U   ′     _     P     =     j                     U   p          [       cos        (   α   )       +     sin        (   α   )         ]                                      
     Control Engineering Model in Fixed Rotor Components 
     With reference to FIG. 4 (control engineering equivalent circuit diagram of the synchronous machine in the normal case) and FIG. 5 (control engineering equivalent circuit diagram of the synchronous machine in the error case), the following equations are obtained for the two cases: 
     Normal Case                  U   d     =         R   S     *     I     S                 D         +       L   S                 l                   s                 d          t         -     ω   *     L   S          I   sq                
            U   q     =         R   S     *     I   sq       -       L   S     *     I   sd       +     U   P                 (   1.5   )                                
     Error Case                  U   d     -       R   S     *     I   Sd       +       L   S                 l                   s                 d          t         -     ω   *     L   S          I   sq       -       U   P          sin        (   α   )                
            U   q     =         R   S     *     I   sq       -       L   s                 l                   s                 d          t         -     ω   *     L   S          I   sd       +       U   P          sin        (   α   )                     (   1.6   )                                
     where I sq , U q  quadrature-axis current and voltage component of the drive 
     I Sd , U d  current and voltage component of the drive 
     ω angular velocity of the d-q coordinate system 
     Ψ P  magnetic flux generated by the permanently excited rotor 
     Ls stator inductance 
     Rs stator resistance 
     In the normal case (α=0, no offset of rotation speed-position sensor  12  ), the d-q coordinate systems of controller  78  and drive  10  are identical. If the response characteristic of converter  14  is disregarded, components UD_SOLL and UQ_SOLL preset by controller  78  correspond to voltages components Ud and Uq, respectively, of drive  10 . 
     In the event of an error (α≠0), the d-q coordinate systems of controller  78  and drive  10  are no longer identical. The quadrature-axis components and direct-axis components (Ud. Isd, Uq, Isq) in the drive deviate from those in controller  78  (UD_SOLL, ID_SOLL, UQ_SOLL, IQ SOLL) because of the sensor offset (α≠0). Angular velocity ωm of the rotor is detected by slipping rotation speed-position sensor  12 , and after multiplying by the number of pole pairs p according to FIG. 3, it is sent as angular velocity ω to direct-axis voltage monitoring  79 . Induced voltage Ψ P ·ω (synchronous generated voltage Up) no longer occurs only in the q axis in controller  78 . This yields a significant change in voltage Ud in the d axis (by Up·sin(α)). Since direct-axis current controller  54  still regulates direct-axis current I D  at zero, the change in voltage Ud in the d axis can be detected in the voltage setpoint. Because of the nature of direct-axis current controller, this change in voltage due to sensor offset (α≠0) is reflected in integrator  64 . 
     Therefore, the output quantity of integrator  64  is suitable for determining whether sensor offset has occurred. To do so, the output value of integrator  64  is compared with limit value G in comparator  73 . In the ideal case (sensor offset α=0, no system dead times, consistently accurate information for model parameters L S  and R S ) integrator  64  assumes a value of zero. In the normal case, however, even without sensor offset (α=0), integrator  64  delivers a constant signal which is due to the dead time voltage (switch dead time of the PWM stage), the induced synchronous generated voltage (following the dead time of direct-axis current controller  54 ) and fluctuating model parameters. However, these parameters can be calculated in advance and taken into account in the form of limit value G. If limit value CG is exceeded by a certain value, then the error results from sensor offset α. In this case, an error signal  75  is generated, e.g., in conjunction with the message “slipping sensor.” 
     Although in principle, the I component of quadrature-axis current controller  48  could also be used to analyze the sensor offset, an advance calculation is made difficult by a fluctuating quadrature-axis current setpoint IQ_SOLL under some circumstances. 
     FIG. 2 shows the controller structure of an asynchronous machine. The essential difference from the synchronous machine is that (direct-axis current setpoint ID_SOLL is not fixed at a value of zero, but instead is generated in the manner shown here. However how it is generated is not essential for the present invention, but instead is mentioned only for the sake of thoroughness, because they function as input quantities for direct-axis voltage monitoring  79  according to FIG.  2 . Thus, direct-axis voltage monitoring  79  according to FIG.  3  and plausibility check  34  can also be used for the asynchronous machine. 
     In the embodiment according to FIG. 6, a dual measuring system monitoring concept has been implemented for the asynchronous machine. At low frequencies, direct-axis voltage monitoring  79  is identical to that in FIG.  3 . 
     Because of parameter tolerances (temperature dependence of the rotor resistance, saturation phenomena), this method is subject to errors at higher frequencies. These parameter deviations can be compensated by an additional controller which adjusts transformation angle φ that the induced voltage in the d axis is zero. The result is that the method of direct-axis voltage monitoring  79  cannot he used at a high rotation speed. while d-q coordinate systems in controller  78  and in drive  10  are in sufficiently good agreement even with a slipping sensor  12 . It is thus possible to obtain sufficiently accurate rotation speed information n_modell from the internal quantities of controller  79  over a rotation speed monitoring model  89 . The output signal of comparator  73  goes as direct-axis voltage error signal  75  to reversing switch  93 . At low values of estimate n_modell, reversing switch  93  relays error signal  75  of direct-axis voltage monitoring  79  to the output as resultant error signal  94 . Otherwise, reversing switch  93  relays model error signal  92  generated by comparator  91 . Comparator  91  determines a significant deviation in the signal delivered by rotation speed-position sensor  12  from the output signal of rotation speed monitoring model  89 , estimate n_modell of the actual rotation speed. Reversing switch  93  is driven as a function of estimate n_modell. 
     FIG. 7 shows rotation speed monitoring model  89 . It essentially emulates the controlled system of drive  10 . Quantities formed by controller  78  such as quadrature-axis current setpoint IQ_SOLL, quadrature-axis voltage setpoint UQ_SOLL, direct-axis current actual value ID_IST and flux actual value FLUSS_IST are used as input quantities. In addition, parameters of drive  10  such as stator resistance  95 , rotor resistance  96  and stator inductance  97  are also input.