Abstract:
An electric drive has at least one electric motor and a power converter feeding electrical motor current thereto. A current desired-value emitter generates a reference signal. An additional circuit is coupled to the current desired-value emitter so as to receive the reference signal and generates a current desired-value signal. A current regulator is coupled to the additional circuit so as to receive the current desired-value signal. The current regulator generates a control signal to the power converter so as to regulate the motor current as a function of the current desired-value signal. The additional circuit has a first mode wherein the current desired-value signal corresponds to the reference signal and a second mode wherein the current desired-value signal is a pulsed signal.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the United States national phase application of PCT/EP2008/003237, filed Apr. 23, 2008, which claims priority from German patent application Serial No. DE102007021632.9, filed May 9, 2007, the entire content of each application is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to an electric drive having at least one electric motor to which an electrical motor current is or can be fed by means of a power converter. The driving has a current regulator by means of which the motor current is or can be regulated as a function of a current desired-value signal by action taken on the power converter. The drive has a current desired-value emitter which is coupled to the current regulator and by means of which a reference signal is or can be generated for the current regulator. The invention also relates to a wind power generator system having a drive of this kind, to a use of a drive of this kind and to a method of adjusting the position of at least one blade of the rotor of a wind power generator system. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wind power generator systems regulate the position of the rotor blades using converter-equipped drives acting as pitch-control drive systems. So that the maximum load carrying capacity of the converters is not exceeded, the actual current at any given time is monitored. The permitted limiting current of the converters is so designed that a dynamic peak current is permitted for a defined length of time and is then reduced to the rated current of the units. It is known that the current permitted under dynamic conditions is equal to twice the rated current of the given unit. Typical drives allow 1.5 to 2 times the rated current of the unit a usual value for the dynamic current. 
         [0004]    The converters which are used for D.C. drives are typically four-quadrant converters having B6 thyristor bridges connected in parallel, but oriented in opposite directions to one another. The dynamic current typically is available for 6 seconds in the converter. However, a period of 6 seconds is only achieved if there is no pre-existing load whatever on the converter. A reduction then takes place to the continuous current or rated current which is set. 
         [0005]    The value of the dynamic current and its duration are preset at fixed values, with the monitoring of the current being performed by means of a monitoring circuit. With certain pre-existing loads, it may happen that all that the converter will then permit is the rated current. Depending on the load torque, this may result in the required revolution speed not being reached, which may result in the drive stopping. Particularly if there are resistances in the mechanical transmission, it may thus happen that the drive stalls and that it is erroneously switched off by the master fault monitoring system. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention improves an electric drive in such a way that it can be operated at comparatively high currents for a longer time. 
         [0007]    The electric drive according to the invention, particularly for adjusting the position of at least one rotor blade of a wind power generator system, has at least one electric motor to which an electrical motor current is or can be fed by means of a power converter. The drive has a current regulator by means of which the motor current is or can be regulated as a function of a current desired-value signal by action taken on the power converter, and a desired-value emitter for current which is coupled to the current regulator and by means of which a reference signal is or can be generated for the current regulator. The current desired-value emitter is coupled to the current regulator via an intervening additional circuit. In a first mode, the reference signal or a signal corresponding to the reference signal can be fed to the current regulator as the current desired-value signal from the additional circuit. In a second mode, a pulsed signal is or can be generated and is or can be fed to the current regulator as the current desired-value signal from the additional circuit. 
         [0008]    Because, by means of the additional circuit, a pulsed signal is or can be generated and is or can be fed to the current regulator as a current desired-value signal is possible for the electric motor to be supplied with a pulse of current in a second mode. This results in the rms value of the current flowing through the power converter being reduced, but in the electric motor nevertheless being able to put out a high torque for the duration of each pulse. In the pulsed mode, the power converter is thus able to be operated at a high current (in the form of pulses) for a longer time than in the unpulsed mode. In particular, it is easier for resistances in the mechanical transmission to be overcome by pulsed operation lasting for a certain length of time than it is by a torque which acts continuously (without being pulsed) and which is available for only a relatively short time. The signal height of the pulses is preferably sufficiently large in this case for 1.5 to 2 times the rated current to flow through the power converter during the pulses. Between the pulses the signal height of the pulsed signal is lower, and the rated current or a lower current thus flows through the power converter between the pulses. What is to be understood by rated current in this case is in particular the rated current of the power converter. However, the exact values for the signal heights of the pulsed signal during the pulses and between the pulses can be set to preferred figures. In particular, the temporal duration of the pulses and/or the duration of the time between the pulses can be set. These temporal durations and durations of time are preferably of a size such that the speed of the current regulation is sufficient for the pulsed signal to be followed. 
         [0009]    The pulsed signal may for example be a square-wave signal or a sawtooth signal or a sinusoidal signal, etc. The pulsed signal is preferably a periodic signal whose frequency can be set. 
         [0010]    The signal corresponding to the reference signal is preferably generated by means of the additional circuit or can be generated by means thereof. The current desired-value signal is generated or can be generated by means of the additional circuit both in the first mode and in the second mode. In the first mode the current desired-value signal is preferably generated as a copy of the reference signal and in the second mode the current desired-value signal is preferably generated as the pulsed signal. 
         [0011]    In a refinement, the pulses in the pulsed signal form at least two groups of pulses which succeed one another at an interval of time which is greater than the interval of time between two successive pulses in the same group of pulses. By this means too it is possible to overcome any overloading of the power converter, because there is a period free of pulses between two successive groups of pulses. In this pulse-free period, the signal height of the current desired-value signal is preferably such that the rated current flows through the power converter. 
         [0012]    What is more, the temperature of the power converter may be monitored by means of the additional circuit. For this purpose, the additional circuit is preferably coupled to a temperature sensor by means of which the temperature of the power converter is or can be measured. The signal height of the pulses in the pulsed signal is or can be varied, and in particular reduced, by means of the additional circuit if the measured temperature reaches or exceeds a preset maximum temperature. The purpose of this provision too is to protect the power converter against overloading. The temperature measurement can be made directly at the power converter or at a body, such as a heat sink, which is thermally coupled to the power converter. 
         [0013]    The additional circuit is preferably able to monitor the reference signal in the first mode, which means that the additional circuit switches or can switch to the second mode if the reference signal or the magnitude thereof is equal to or greater than a preset maximum value for a preset period of time. In particular, the additional circuit may monitor the reference signal in the second mode too, meaning that the additional circuit switches or can switch to the first mode if the reference signal or the magnitude thereof drops below a preset threshold value which is equal to or smaller than the maximum value. 
         [0014]    The current desired-value emitter is preferably part of a speed regulator which regulates or can regulate the motor speed particularly in the first mode, or it may be the speed regulator. The current desired-value emitter preferably forms a speed-correcting means for the speed regulator (though as an alternative the speed-correcting means may also be called a speed regulator). In this case the reference signal is dependent on a difference between a desired electric motor speed and an actual speed thereof. In particular, the reference signal is generated as a function of a difference between the desired speed for the electric motor and the actual speed. The electric drive thus preferably has speed regulation with downstream or secondary current control. The reference variable for current regulation may be supplied by the speed regulator or in other words by the speed-correcting means thereof. Hence it is easily possible for the invention to be incorporated in an existing electric drive by breaking the connection between the speed-correcting means or speed regulator and the current regulator and inserting the additional circuit between them. 
         [0015]    The electric motor is preferably a D.C. electrical machine which is operated and/or switched in particular as a series-wound electrical machine. 
         [0016]    The current regulator can act on the power converter to regulate the motor current or acts on the power converter to regulate the motor current. The power converter is therefore preferably a controllable power converter which is or can be controlled or regulated in particular by means of the current regulator. The power converter preferably comprises one or more thyristors on whose gate terminal or gate terminals the current controller acts or can act directly or indirectly. 
         [0017]    The power converter is or can be supplied with multi-phase power, the multi-phase power preferably being two-phase power or three-phase power. The power converter may have at least one multi-phase thyristor bridge to which the multi-phase power is or can be applied. The multi-phase thyristor bridge is preferably a two-phase or three-phase thyristor bridge. In particular the power converter has two B6 thyristor bridges which are connected in parallel, but oriented in opposite directions to one another, and which are or can be supplied with three-phase power. 
         [0018]    The current regulator and/or the current desired-value emitter may take a digital form. The current regulator is preferably an analogue regulator, which means that the reference signal and/or the current desired-value signal are also preferably analogue signals. The current desired-value emitter and/or the speed-correcting means are also preferably analogue circuits. The speed regulator is also an analogue regulator. The additional circuit by contrast preferably has a digital processor. So that the processor is able to take in and process or rather evaluate the analogue signals, the additional circuit preferably has at least one analogue-to-digital converter by means of which the reference signal can be read in and digitized, and at least one digital-to-analogue converter by means of which the current desired-value signal can be emitted. Alternatively, it is possible for the additional circuit to be implemented in analogue form. 
         [0019]    The invention also relates to a wind power generator system having a support, a rotor which is mounted on the support to be able to turn about a rotor axis and which has a rotor hub, and at least one rotor blade fastened to the rotor hub whose position relative to the rotor hub is or can be adjusted by means of a pitch-control drive, the pitch-control drive having at least one drive according to the invention which may be refined in conformity with all the embodiments mentioned. 
         [0020]    To allow rotor blade position adjustment, it is preferably mounted on the rotor hub to be rotatable about a blade axis and can be turned by means of the pitch-control drive about the blade axis, which extends obliquely or perpendicularly to the rotor axis. 
         [0021]    The invention also relates to the use of an electric drive for adjusting the position of at least one rotor blade of a wind power generator system, the electric drive being a drive according to the invention which may be refined in conformity with all the embodiments mentioned. 
         [0022]    The invention relates in addition to a method of adjusting the position of at least one rotor blade of a wind power generator system by means of at least one electric motor to which an electric motor current which is regulated as a function of a current desired-value signal is fed by means of a power converter, a reference signal being generated to which the current desired-value signal corresponds in a first mode. There is a also a pulsed signal, to which the current desired-value signal corresponds in a second mode, which is generated if the reference signal or the magnitude thereof exceeds a preset maximum value for a preset period of time. 
         [0023]    A change is preferably made back to the first mode if the reference signal or the magnitude thereof drops below a preset threshold value which is equal to or smaller than the maximum value. 
         [0024]    The speed of the electric motor is preferably regulated, in particular in the first mode. When this is done the reference signal is preferably dependent on the difference between a desired electric motor speed and its actual speed. In particular, the reference signal is generated as a function of the difference between the desired speed and the actual speed. 
         [0025]    The temperature of the power converter is preferably measured, the signal height of the pulses in the pulsed signal being varied, and in particular reduced, if the temperature which is measured reaches or exceeds a preset maximum value for temperature. 
         [0026]    The electric motor is in particular a D.C. electrical machine. Also the power converter preferably has a multi-phase current, and in particular a two-phase current or three-phase current, fed to it. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a schematic side view of a wind power generator system having an electric drive which conforms to one embodiment of the invention. 
           [0028]      FIG. 2  is a schematic block diagram of the embodiment of the drive. 
           [0029]      FIG. 3  is a schematic block diagram of the additional circuit shown in  FIG. 2 . 
           [0030]      FIG. 4  is a flow chart for the additional circuit shown in  FIG. 3 . 
           [0031]      FIG. 5  shows a waveform over time of the output signal from the additional circuit. 
           [0032]      FIG. 6  shows another waveform over time of the output signal from the additional circuit. 
           [0033]      FIG. 7  is a circuit diagram of the power converter. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]      FIG. 1  provides a side view of a wind power generator system  1  which has a tower  2  which is anchored in the ground  4  by means of a foundation  3 . At the end of the tower  2  remote from the foundation  3 , a machinery support  5  is mounted on the tower  2  in such a way as to be rotatable about the longitudinal axis  7  of the tower  2  by means of an azimuth system  6 . A rotor  8  is mounted on the machinery support  5  to rotate about a rotor axis  9 . The rotor has a hub  10  and a plurality of rotor blades  11  which are each able to be turned relative to the rotor hub  10  about a blade axis  12 . The blades axes  12  extend perpendicularly or obliquely to the rotor axis  9 . Each of the rotor blades  11  may be turned about its blade axis  12  by means of a pitch-control drive  13 . The rotor  8  can be turned about the rotor axis  9  by the wind  14  and can drive an electric generator  15 . Also, each of the pitch-control drives  13  is electrically coupled to a system controller  16  which actuates or can actuate the pitch-control drives  13  to turn the rotor blades  11 . Each of the pitch-control drives  13  has an electric drive  85  (see  FIG. 2 ) which forms an embodiment of the invention, or is formed by a drive  85  of this kind. 
         [0035]      FIG. 2  provides a schematic block circuit diagram of one of the electric drives  85 . The drive  85  is fed a desired-value speed signal  17  from which an actual-value speed signal  18  is subtracted. A speed difference signal  19  is fed to a speed-correcting portion  20 . The speed-correcting portion  20  is electrically connected to a current regulator  22  via an intervening additional circuit  21 . The speed-correcting portion  20  generates a reference signal  23  for the current regulator  22  as a function of the speed difference signal  19  and transmits it to the additional circuit  21 . The additional circuit  21  transmits a current desired-value signal  24  to the current regulator  22 . 
         [0036]    The current regulator  22  has a current-correcting portion  25  which has a controllable power converter  26  connected downstream of it. A current actual-value signal  27  is subtracted from the current desired-value signal  24 , and the current difference signal  28  is fed to the current-correcting portion  25 . The current-correcting portion  25  generates a control signal  29  as a function of the current difference signal  28  and transmits it to the power converter  26 . The power converter  26  supplies an electrical current  30  to an electric motor  31 , which takes the form of a D.C. electrical machine in the present case, as a function of the control signal  29 . The speed  32  of the electric motor  31  is measured by a speed-measuring element  33  which generates the speed actual-value signal  18 , which represents the present speed  32  of the electrical motor  31 . Also, the electric current  30  is measured by a current-measuring element  34  which generates and transmits the current actual-value signal  27  which represents the electric current (motor current)  30  which is flowing at the time through the electric motor  31 . 
         [0037]    In  FIG. 2 , reference numeral  84  identifies the speed regulator. As an alternative, it might however equally well be the speed-correcting portion  20  that was identified as the speed regulator. Also, in  FIG. 2  reference numeral  22  identifies the current regulator. As an alternative, it might however equally well be the current-correcting portion  25  that was identified as the current regulator. 
         [0038]      FIG. 3  provides a schematic block circuit diagram of the additional circuit  21 , which has an analogue-to-digital converter  35  which converts the analogue reference signal  23  into a digital reference signal  36 . The digital reference signal  36  is fed to a digital processor  37  which evaluates the digital reference signal  36  and generates and emits a digital current desired-value signal  38  as a function of its evaluation. The digital current desired-value signal  38  is fed to a digital-to-analogue converter  39  which converts the digital current desired-value signal  38  into the analogue current desired-value signal  24 . Also provided is a temperature sensor  53  which is thermally coupled to the power converter  26 . The temperature signal  79  emitted by the temperature sensor  53  represents the present temperature of the power converter  26  and is fed to an analogue-to-digital converter  80  which converts the analogue temperature signal  79  into a digital temperature signal  81  which is fed to the processor  37 . The digital temperature signal  81  is evaluated by the processor  37  and if required is taken into account in the generation of the digital current desired-value signal  38 . The temperature sensor  53  is preferably a KTY sensor. 
         [0039]    The process which takes place in the additional circuit  21 , or rather in the processor  37 , will be described in what follows by reference to the flow chart which can be seen in  FIG. 4 . This flow chart merely indicates one of several possible implementations in this case and the flow chart in  FIG. 4  should therefore not be construed as limiting. 
         [0040]    First, in step  40 , the additional circuit  21  is set to a first mode. In the first mode, the current desired-value signal (I_desired)  24  always corresponds to the reference signal (I_f)  23 , and the transfer function of the additional circuit  21  is thus equal to “1” or approximately equal to “1”. This being the case, the electric drive  85  forms an electric motor  31  which has a speed regulator  84  which is secondary to the current regulator  22 . 
         [0041]    In step  41 , the reference signal I_f is determined and in step  42  it is checked whether the reference signal I_f is equal to or greater than a preset maximum value I_max. If it is not, a change is made back to step  41 . If the result of the check in step  42  is positive, a timer is started in step  43 . When interrogated, the timer supplies that period of time Δt which has elapsed between the time when the timer was started and the time of the interrogation. Consequently, what applies at the time when the timer is started is Δt=0. Following this, in step  44 , the reference signal I_f is determined again and in step  45  is it checked whether the reference I_f is equal to or greater than the maximum value I_max. If it is not, a change is made back to step  41 . If the result of the check in step  45  is positive, then the timer is interrogated in step  46  and, as a result of the interrogation, the period of time Δt which has elapsed from the time when the timer was started in step  43  to the time of the interrogation in step  46  is delivered. 
         [0042]    In step  47  it is checked whether the period of time Δt supplied as a result of the interrogation is equal to or greater than a maximum time t_max. If it is not, a change is made back to step  44 . If the result of the check in step  47  is positive, then the additional circuit  21  is set to a second mode in step  48 . In the second mode, a pulsed signal I_puls (see  FIG. 5 ) is generated by the additional circuit  21  and is emitted as the current desired-value signal, I_desired. 
         [0043]    In step  49  the reference signal I_f is read in and in step  50  it is checked whether the reference signal I_f is equal to or greater than the maximum value I_max. If it is not, a change is made back to step  40  and the additional circuit  21  is set back to the first mode. If the result of the check in step  50  is positive, the temperature T of the converter  26  is determined in step  51 . An evaluation of the temperature T which has been determined then follows in step  52 , after which a change is made back to step  49 . 
         [0044]    The evaluation in step  52  of the temperature T which has been determined may comprise in particular a reduction in the signal height I_dyn (see  FIG. 5 ) of the pulses in the pulsed signal I_puls if the temperature T which has been determined reaches or exceeds a preset maximum temperature T_max. 
         [0045]    A possible waveform for the current desired-value signal I_desired as a function of time t can be seen in  FIG. 5 . Initially, the additional circuit  21  is in the first mode in which the current desired-value signal I_desired corresponds to the reference signal I_f. At first, the current desired-value signal I_desired is below the maximum value I_max but as the time t goes on it rises and at time t_ 0  it reaches the maximum value I_max. Since the current desired-value signal I_desired then does not drop below the maximum value I_max for the preset period of time t_max, the additional circuit  21  switches over to the second mode at time t_ 0 +t_max. The pulsed signal I_puls is now generated and is emitted as the current desired-value signal I_desired until, at t_ 1 , the reference signal I_f again drops below the maximum value I_max. In  FIG. 5  the pulsed signal is a square-wave signal. Other pulse shapes are possible however. 
         [0046]    The signal height I_dyn of the pulses in the pulsed signal I_puls is equal to I_max in the present case. This preferably results in the current flowing through the power converter  26  corresponding to twice the rated current of the power converter during the pulses. Between the pulses, the signal height of the pulsed signal I_puls is I_rec, which is preferably sufficiently high for the current flowing through the power converter  26  during the time t_rec between the pulses to correspond to the rated current of the power converter  26  or to a lower current. The time t_rec between the pulses is equal in the present case to the pulse length t_puls, and the pulsed signal I_puls thus has a mark-to-space ratio of, preferably, 0.5. A typical value for t_puls=t_rec is for example 1s, although this value should not be construed as limiting. 
         [0047]    At t_ 1 , the additional circuit  21  switches back to the first mode, in which the current desired-value signal I_desired corresponds to the reference signal I_f. However, at t_ 2  the current desired-value signal I_desired again reaches the maximum value I_max and remains there for the time t_ 2 +t_max, thus causing a switch to be made to the second mode and the pulsed mode to be initiated. Also, it is found at time t_ 3  that the temperature T of the power converter  26  has reached or exceeded the preset maximum temperature T_max, and the signal height I_dyn of the pulses in the pulsed signal I_puls is therefore reduced to a value which is less than I_max. 
         [0048]    From  FIG. 6  can be seen the waveform over time of the current desired-value signal I_desired in a modification in which a group of pulses  82  comprising five pulses is first generated and emitted in the pulsed mode (second mode), starting from t_ 0 +t_max. Following this there is a refresh period t_refresh in which no pulses are emitted. On expiry of the refresh period t_refresh, a group of pulses  83  comprising five pulses is again emitted as the current desired-value signal I_desired, after which there is again a refresh period t_refresh. This sequence is repeated for as long as the pulsed mode continues. The number of pulses in each group of pulses is not limited to five in this case but can also be set to some other figure. Also, a reduction in the signal height of the pulses is possible in this case too if the temperature T of the power converter  26  reaches or exceeds the maximum temperature T_max. 
         [0049]      FIG. 7  provides a circuit diagram of the power converter  26 , which has a first B6 thyristor bridge  54  and a second B6 thyristor bridge  55 , the two thyristor bridges  54  and  55  being connected in parallel but being oriented in opposite directions to one another. Each of the thyristor bridges  54  and  55  has six thyristors  56 , with the gate terminals of the thyristors  56  in the thyristor bridge  54  being connected to a pulse transformer  57  and the gate terminals of the thyristors  56  in the thyristor bridge  55  being connected to a pulse transformer  58 . The pulse transformers  57  and  58  are connected to a phase-control module  59  to which the control signal  29  emitted by the current-correcting portion  25 , which preferably represents the delay angle at the time, is fed as an input signal. 
         [0050]    A first output line  60  from the thyristor bridges  54  and  55  is connected to one end of the rotor winding  62  of the electric motor  31  via an intervening fuse  61 . Also, the other end of the rotor winding  62  is connected to one end of the stator winding  65  of the electric motor  31  by a lead  63  via an intervening diode array  64 . The second output line  66  from the thyristor bridges  54  and  55  is connected to the other end of the stator winding  65  via the intervening diode array  64 . The electric motor  31  is operated as a series-wound electrical machine in the present case, with the four diodes  67  of the diode array  64  ensuring that current always flows through the stator winding  65  in the same direction. It is thus possible for the current through the rotor winding  62  to be reversed without the current through the stator winding  65  reversing. A change in the direction of rotation of the rotor can be brought about in this way. 
         [0051]    The two thyristor bridges  54  and  55  are connected by connections  68 ,  69  and  70  and lines  74 ,  75 , and  76  to the three phases of a three-phase mains supply, with a series circuit comprising a fuse  71  and a reactor  72  being inserted in the line associated with each phase. Three varistors  73  are also connected between the lines  74 ,  75  and  76  to serve as over-voltage protection. 
         [0052]    Inserted in the lines  75  and  76  are current transformers  77  and  78  by means of which the current flowing through the thyristor bridges  54  and  55  can be measured. The two current transformers  77  and  78  thus form the sensor part of the current-measuring means  34 . The current which is measured also represents in this case the current which flows through the motor  31  and which is thus suitable to form the current actual-value signal  27 . 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 Wind power generator system 
               
               
                 2 
                 Tower 
               
               
                 3 
                 Foundation 
               
               
                 4 
                 Ground 
               
               
                 5 
                 Machinery support 
               
               
                 6 
                 Azimuth system 
               
               
                 7 
                 Longitudinal axis of tower 
               
               
                 8 
                 Rotor 
               
               
                 9 
                 Rotor axis 
               
               
                 10 
                 Rotor hub 
               
               
                 11 
                 Rotor blade 
               
               
                 12 
                 Blade axis 
               
               
                 13 
                 Pitch-control drive 
               
               
                 14 
                 Wind 
               
               
                 15 
                 Electrical generator 
               
               
                 16 
                 System controller 
               
               
                 17 
                 Speed desired-value signal 
               
               
                 18 
                 Speed actual-value signal 
               
               
                 19 
                 Speed difference signal 
               
               
                 20 
                 Speed-correcting portion/current desired-value emitter 
               
               
                 21 
                 Additional circuit 
               
               
                 22 
                 Current regulator 
               
               
                 23 
                 (Analogue) reference signal 
               
               
                 24 
                 (Analogue) current desired-value signal 
               
               
                 25 
                 Current-correcting portion 
               
               
                 26 
                 Power converter 
               
               
                 27 
                 Current actual-value signal 
               
               
                 28 
                 Current difference signal 
               
               
                 29 
                 Control signal 
               
               
                 30 
                 Electric current/motor current 
               
               
                 31 
                 Electric motor 
               
               
                 32 
                 Speed of electric motor 
               
               
                 33 
                 Speed-measuring element 
               
               
                 34 
                 Current-measuring element 
               
               
                 35 
                 Analogue-to-digital converter 
               
               
                 36 
                 Digital reference signal 
               
               
                 37 
                 Digital processor 
               
               
                 38 
                 Digital current desired-value signal 
               
               
                 39 
                 Digital-to-analogue converter 
               
               
                 40 
                 Step: Set additional circuit to first mode 
               
               
                 41 
                 Step: Determine reference signal 
               
               
                 42 
                 Step: Check whether reference signal equal to or greater than 
               
               
                   
                 maximum value 
               
               
                 43 
                 Step: Start timer 
               
               
                 44 
                 Step: Determine reference signal 
               
               
                 45 
                 Step: Check whether reference signal equal to or greater than 
               
               
                   
                 maximum value 
               
               
                 46 
                 Step: Interrogate timer for period of time 
               
               
                 47 
                 Step: Check whether period of time supplied equal to or greater 
               
               
                   
                 than maximum value 
               
               
                 48 
                 Step: Set additional circuit to second mode 
               
               
                 49 
                 Step: Determine reference signal 
               
               
                 50 
                 Step: Check whether reference signal equal to or greater than 
               
               
                   
                 maximum value 
               
               
                 51 
                 Step: Determine temperature of power converter 
               
               
                 52 
                 Step: Evaluate temperature determined 
               
               
                 53 
                 Temperature sensor 
               
               
                 54 
                 B6 thyristor bridge 
               
               
                 55 
                 B6 thyristor bridge 
               
               
                 56 
                 Thyristor 
               
               
                 57 
                 Pulse transformer 
               
               
                 58 
                 Pulse transformer 
               
               
                 59 
                 Phase-control module 
               
               
                 60 
                 Line 
               
               
                 61 
                 Fuse 
               
               
                 62 
                 Rotor winding of electric motor 
               
               
                 63 
                 Line 
               
               
                 64 
                 Diode array 
               
               
                 65 
                 Stator winding of electric motor 
               
               
                 66 
                 Line 
               
               
                 67 
                 Diodes 
               
               
                 68 
                 Connection 
               
               
                 69 
                 Connection 
               
               
                 70 
                 Connection 
               
               
                 71 
                 Fuse 
               
               
                 72 
                 Reactor 
               
               
                 73 
                 Varistor 
               
               
                 74 
                 Line 
               
               
                 75 
                 Line 
               
               
                 76 
                 Line 
               
               
                 77 
                 Current transformer 
               
               
                 78 
                 Current transformer 
               
               
                 79 
                 (Analogue) temperature signal 
               
               
                 80 
                 Analogue-to-digital converter 
               
               
                 81 
                 Digital temperature signal 
               
               
                 82 
                 Group of pulses 
               
               
                 83 
                 Group of pulses 
               
               
                 84 
                 Speed regulator 
               
               
                 85 
                 Electric drive