Abstract:
The invention relates to a device and a method for monitoring the connection of an electrical supply unit comprising voltage detection ( 32 ) detecting phase voltage ( 14 ), current detection ( 32 ) detecting phase voltages ( 38 ), a transformation unit ( 66 ) transforming the phase voltages ( 38 ) after conducting field-oriented regulation in at least one cross current ( 62 ), wherein a monitoring device ( 34 ) is provided to monitor at least one supply connection ( 28, 36 ) by means of which an electrical supply unit ( 32 ) is supplied, said monitoring unit evaluating the variation of the cross current ( 62 ) in order to monitor the connection.

Description:
BACKGROUND OF THE INVENTION 
   The invention is based on a device and a method for monitoring the connection of an electrical supply unit. From German Patent DE 42 13443 C1, a circuit arrangement for monitoring the failure of fuses is already known. The fuses are each connected into the current paths of a rotary current network for supplying a consumer. The circuit arrangement has a first delta-connection circuit for detecting the phase of a voltage between each two conductors of the rotary current network upstream of the fuses and a second delta circuit for detecting the phase of a voltage between each two conductors of the rotary current network downstream of the fuses. The respective phases upstream and downstream of the fuses are compared with one another, and a failure signal is output if a phase difference occurs, or if one or more phases are absent. This circuit is also suitable for monitoring the connection of an electrical supply unit. 
   The object of the invention is to disclose a device for monitoring the connection which in particular reduces the requisite hardware expense for that purpose. This object is attained by the characteristics of the independent claim. 
   SUMMARY OF THE INVENTION 
   The device according to the invention for monitoring the connection of an electrical supply unit has a voltage detector, which ascertains the phase voltages. A current detector is also provided for detecting the phase currents. A transformation unit converts the phase currents, on the theory of field-oriented regulation, into at least one transverse current. According to the invention, for monitoring at least one supply connection, by way of which an electrical supply unit is supplied, a monitoring device is provided, which evaluates the course of the transverse current for monitoring the connection, and in particular in servo drives, recourse is had to field-oriented regulation. In the course of the field-oriented regulation, the requisite coordinate transformations of the phase variables into transverse and longitudinal variables are performed. The transverse current, in particular, is thus already available in field-oriented regulation. According to the invention, this transverse current is now evaluated for the purpose of monitoring the connection. This is because it has been demonstrated that particularly the polarity of the transverse current during the activation course is an unambiguous indication whether the phase connections of the supply unit have been transposed. Only if connection is done correctly is the transverse current course always below a defined limit value, in this case I=0. In all other cases, conversely, in which the transverse current permanently or briefly assumes a positive value during the activation operation, it can be concluded that there is faulty connection wiring. This monitoring the connection can thus be done purely by software. Additional hardware is no longer needed. This makes the corresponding monitoring device less expensive. 
   In an expedient refinement, it is provided that the monitoring device, for monitoring the connection, ascertains the various phase powers from the phase voltages and phase currents and evaluates them. In particular the sign of the resultant powers can in turn be evaluated as an indication of whether phases have been transposed with one another and if so which phases and in which way. In the monitoring of a three-phase rotary current network for supplying the electrical supply unit, if there is only one positive phase power it can be concluded that the other two phases of negative power have been transposed. By including the phase-related powers, an unambiguous connection fault diagnosis can be achieved purely computationally without requiring additional hardware. 
   In an expedient refinement, it is provided that the monitoring device evaluates the longitudinal current for monitoring the connection. Particularly if all the phase-related powers are negative, the phase shift by either +120° or −120° can be detected unambiguously from the longitudinal current. By including the longitudinal current, all possible faulty connections can now be detected unambiguously. Since on the other hand the longitudinal current is already available in the context of field-oriented regulation, this evaluation assures low effort and expense for computation. Further expedient refinements will become apparent from the further dependent claims and from the description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One exemplary embodiment of the device of the invention is shown in the drawing and will be described in further detail below. 
     Shown are 
       FIGS. 1   a  and  1   b , the basic layout of the device for monitoring the connection; 
       FIG. 2 , the monitoring program that runs in the device for monitoring the connection; and 
       FIGS. 3 through 8 , typical courses of the longitudinal current and transverse current with the associated intermediate circuit voltage, for different connections of the three phases of a rotary current network. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Via a network connection  12 , the three phases U, V, W of a rotary current network (360 to 510 V, 50/60 Hz) are supplied to a network connection unit  10 . Each of the three phases U, V, W is protected via a fuse  20 . Downstream of the fuses  20  in terms of the network, the phase voltages U U , U V , U W    14  are picked up and delivered to a regulation and control block  34  of a supply unit  32 . This regulation and control block  34  furnishes a first and second protective trigger signal  16 ,  18  for triggering a charge contactor  22  and a network contactor  24 , which is integrated with the network connection unit  10 . If the charge contactor  22  is triggered by a suitable trigger signal  16  in the direction of closure, then the phase currents I U , I V , I W , via charge resistors  26 , reach the respective reactor connection points  28  in the form of outputs of the network connection unit  10 . The charge resistors  26  are bridged by the network contactor  24 , once the charging operation of the intermediate circuit capacitors  44  is ended. This is recognized by means of measuring the intermediate circuit voltage  46 . For each of the phases U, V, W, commutation reactors  30  are now provided, which are to be connected to the three reactor connection points  28 . The other connections of the commutation reactors  30  are connected to the reactor connections  36  of the supply unit  32 . The phase currents I U , I V , I W  delivered via these reactor connections  36  of the supply unit are detected in the supply unit  32  and delivered to the regulation and control block  34 . Six power transistors of the end stage  40 , wired as B 6  bridge, form the DC converter or AC converter block of the supply unit  32 . Each of the transistors is provided with an antiparallel-connected diode as a free-wheeling diode. The end stage  40  is connected by end stage trigger signals  42  from the regulation and control block  34 , in order to convert the supplied three-phase alternating voltage, for supplying for instance an electrical drive mechanism, into a direct voltage. This direct voltage is available in a direct voltage intermediate circuit as an intermediate circuit voltage  46 . For further smoothing of this voltage, intermediate circuit capacitors  44  are provided. The intermediate circuit voltage  46  applied to the intermediate circuit capacitors  44  is likewise delivered to the regulation and control block  34 . 
   The regulation and control block  34  of the supply unit  32  is shown in further detail in  FIG. 1   b . A voltage regulator  50  disposed in the regulation and control block  34  receives as its input variables both an intermediate circuit voltage set-point value  48  and the intermediate circuit voltage  46  as an actual value. From them, the voltage regulator  50  ascertains a transverse current set-point  52 , which is delivered as an input variable to both a current regulator  56  and a transformation and PWM conversion unit  60 . The phase voltages U U , U V , U W    14  are delivered to both a voltage transformer  74  and a reference angle generator  68 . From them, the reference angle generator  68  ascertains the phase angle  67 , which in turn is supplied as an input variable to a current transformer  66  and the voltage transformer  74  as well as to the transformation and PWM conversion unit  60 . From the phase currents I U , I V , I W    38  also supplied, the current transformer  66 , on the principles of field-oriented regulation, generates both a transverse current actual value  62  and a longitudinal current actual value  64 , which serve not only as a longitudinal current set-point value  64  but also serve the current regulator  56  as input variables. As output variables, the current regulator  56  makes both a transverse voltage set-point value  57  and a longitudinal voltage set- point value  59  available to the transformation and PWM conversion unit  60 . The transformation and PWM conversion unit  60  is also supplied with a transverse voltage actual value  70  and a longitudinal voltage actual value  72 , both of them generated by the voltage transformer  74 . The transformation and PWM conversion unit  60  performs a back- transformation of the longitudinal and transverse components to the corresponding phase-related components and generates pulse-width modulated trigger signals for the six transistors of the end stage  40 . External interface signals  19  are also delivered to the regulation and control block  34 . The monitoring process for monitoring the connection that runs in the regulation and control block  32  is shown in  FIG. 2 . 
   In  FIG. 3 , the courses of the transverse current (actual value)  62  and longitudinal current (actual value)  64  and of the intermediate circuit voltage  46  are shown as a function of time. The intermediate circuit voltage  46  rises at the instant of activation, with the course of an exponential function. At the same instant, the transverse current  62  abruptly drops and then rises with the course of an exponential function. However, the transverse current  62  always remains negative; that is, it never exceeds the value I=0. The longitudinal current  64  oscillates around the zero line. In  FIG. 3 , the courses of these variables with correct connection are shown. In  FIG. 4 , the phases U, V, W are cyclically offset by +120°; that is, they have been connected in the sequence V, W, U. Both the transverse current  62  and the longitudinal current  64  then always have positive values and approach the zero line.  FIG. 5  shows an arrangement of the phases cyclically transposed by −120°: The order of connection is W, U, V. Once again, the transverse current  62  is only positive and oscillatingly approaches the value I=0. The longitudinal current  64 , conversely, has only negative values, whose course likewise approaches the value of I=0. In  FIG. 6 , two phases have been transposed: Here the connection order is W, V, U. Both the transverse current  62  and the longitudinal current  64  oscillate about the zero line and reach both positive and negative values. This behavior can also be seen from  FIGS. 7 and 8 . In  FIG. 7 , the phases W and V have been transposed (connection order: U, V, W), while in  FIG. 8  the phases V and U are transposed (connection order: V, U, W). 
   These characteristic current courses are purposefully interrogated in the monitoring program of  FIG. 2  for the sake of monitoring the connection. 
   The supply unit  32  is regulated in field- or network-oriented fashion. According to the theory of vector regulation, the detected phase current I U , I V , I W , after transfer to a field-related orthogonal two-phase system (D-Q coordinate system), can be divided into two components, namely the transverse current  62  and the longitudinal current  64 . The longitudinal current component  64  (reactive current component) builds up the supplied and fed back reactive power of the supply unit  32  and is normally set at the value zero. The transverse current  62  is perpendicular to the longitudinal current  64 ; it is oriented in the same direction as the network voltage and forms a standard for the effective power supplied. 
   The supply unit  32  can be triggered such that it rectifies the alternating voltage of the three-phase alternating voltage network into the intermediate circuit voltage  46  and with this energy from the network supplies an electrical consumer, not shown in detail, such as an inverter which in turn supplies an electric motor. For example, the supply unit  32  includes six controlled power transistors of the end stage  40 , which are triggered in pulse width modulated fashion, for instance at a clock frequency of 8 kHz with a variable pulse width ratio. 
   Thus the current transformer  66 , in the context of field-oriented regulation, already makes the transverse current actual value  62  and the longitudinal current actual value  64  available. According to the invention, now, among others these components are evaluated intentionally for detecting the network phase relationship. The three phases U, V, W of a rotary current network are delivered with the correct phase in the intended way to a network connection unit  10 . The reactor connection points  28  should be connected correctly for each phase U, V, W to the reactor connections  36  of the supply unit via the commutation reactors  30 . A correct connection is shown in  FIG. 1   a . However, there are also possible ways of transposing the network phase order compared to the network connection  12 , as a result of incorrect connection. The result could be that the outputs of the network connection unit  10  for the phases U, V, W are not correctly connected to the phase-related connections of the supply unit  32 . In correct operation, the phases U, V, W of the supply unit  32  should be supplied in the order U, V, W from left to right, as shown in  FIG. 1   a . Incorrect connections are detected by the monitoring method described in conjunction with  FIG. 2 . 
   For starting the supply unit  32 , the charge contactor  22  should be triggered in the direction of closure via the external interface signal  19 , so that the intermediate circuit capacitor  44  can be charged via the charge resistors  26 , serving to limit current, and the free-wheeling diodes of the end stage  40 . The network contactor  24  is opened. In an interrogation block  103 , however, the regulation and control block  34  decides beforehand, by comparison of the intermediate circuit voltage  46  with a fixed limit value, which control mechanism will be chosen (step  105  or step  107 ). For instance, if an intermediate circuit voltage  46  of less than 30% of the intermediate circuit voltage is detected (for example, the supply unit  32  was not yet connected to the network, and the intermediate circuit capacitors  44  are completely discharged), then the routine is started in step  107 . Conversely, if an intermediate circuit voltage  46  greater than 30% of the intermediate circuit voltage is detected (for instance, the supply unit  32  was activated, and, the intermediate circuit capacitors  44  have not yet been completed discharged, or no load currents can flow after the charge contactor  22  has been turned on), then the routine is started in accordance with step  105 , or all three upper transistors 1.1, 1.3, 1.5, or all three lower transistors 2.2, 2.4, 2.6, are triggered via the IGBT triggers  42 . Thus via these transistors and charge resistors  26 , an intentional short circuit is brought about for a length of time that is fixed in the regulation and control block  34 , so that the short-circuit current in this case acts as a substitute charging current, which is what is to be monitored. This is again followed by step  107 . In step  107 , the charge contactor  22  is switched on, and the question is asked whether the network current  30  (charge current or short-circuit current) is flowing. For a predeterminable length of time, the current and voltage courses of the phase currents I U , I V , I W    38  and the phase voltages U U , U V , U W    14  are detected and stored, for instance in digitized form. From these phase-related current and voltage courses, the electrical power is now ascertained for each phase: PU=Σ i U * u U ; p V =Σ i V * u V ; p W =Σ i W * u W , over an integral multiple of a period length. Moreover, in step  107 , the course over time of the transverse current  62  and of the longitudinal current  64 , for instance as it results as shown in  FIGS. 3 through 8 , is ascertained. 
   As the first criterion for whether a correct phase connection of the supply unit  32  exists, in the interrogation block  109  the transverse current  62  is compared with a limit value. If the course over time of the transverse current  62  within a time interval 20 ms—found out via the interrogation block  111 —never exceeds the value I=0, then the conclusion is drawn that the phase connection is correct. A report is for instance issued that phase equality prevails (connection order: U, V, W), in step  121 . No instantaneous value of the transverse current  62  may be greater than zero. Only in that case is the criterion IQ&lt;0 met. 
   If any instantaneous value of the transverse current  62  whatever, within the predeterminable time interval, exceeds the value I=0, then in a further interrogation block  113  it is ascertained whether the phase-related powers p U , p V , p W , ascertained in step  107  are all of them greater than zero. If so, it can be concluded that the phases are cyclically transposed by either +120° or −120°. If that is the case, then in step  115  the course over time of the longitudinal current  64  is evaluated. If one of the instantaneous values of the longitudinal current  64  is positive, this is an indication of a phase shift by +120°. In that case, the supply unit  32  would be cabled as follows: V, W, U. A report accordingly is issued in step  129 . The corresponding course over time of the transverse and longitudinal currents is shown in  FIG. 4 . However, if none of the instantaneous values of the longitudinal current  64  exceeds the value of zero, this means a phase shift by −120°. The connection order in that case is: W, U, V. This corresponds to the course over time of the currents in  FIG. 5 . 
   However, if in the interrogation block  113  it is found that at least one of the phase-related powers p U , p V , p W  assumes a positive value, then it is ascertained which one of the phase-related powers p U , p V , p W  is that value. If the power of the phase U is greater than zero, as asked in step  117 , this means that the phases V and W are transposed; the connection order is U, V, W. In step  123 , a report accordingly is generated. The associated current courses are shown in  FIG. 7 . However, if the power of phase U is less than zero, then in step  119  it is checked whether the power in phase V is positive. If so, then in step  127  the following report is issued: The phases U and W are transposed with one another. The connection order now looks like this: W, V, U, with the associated current course as in  FIG. 6 . If the power in phase V is no greater than zero either, then what remains, as the last possible type of fault, is that the phases U and V are transposed. The corresponding fault report is generated in step  125 . The phase order is now V, U, W, with the associated current course shown in  FIG. 8 . 
   Thus now all the possibilities of transposition of the phase connections of the supply unit  32  are reliably detected. Besides the corresponding displays, still other countermeasures can be initiated, in which for instance the PWM trigger  60  and thus the transistors of the end stage  60  are synchronized with the actual detected network phase order. It is thus possible for the supply unit  40  to be operated with the “wrong phase relationship”.