Electric motor drive

Abstract

The invention relates to an electric motor drive for operating an alternating-current motor. The electric motor drive comprises a frequency converter, for controlling the electric motor, that includes a rectifier and an inverter implemented using semiconductor switches arranged in a bridge, and an intermediate circuit comprising a capacitor and placed between the rectifier and the inverter. The electric motor drive additionally comprises two regulating units. The first regulating unit contains an inductor unit at the input of the frequency converter and at the input of the rectifier, where the inductors comprised in the unit being connected to each phase; and an intermediate circuit with a low-value capacitor of 50 μF. The second regulating unit comprises an auxiliary switch, to which the supply of electric power is arranged to occur via a safety relay and a current measuring unit. The auxiliary switch is connected to each semiconductor switch of the inverter bridge in which the control signal for each semiconductor switch will pass via the auxiliary switch when the auxiliary switch is in a conducting state. The current measuring unit measures and/or monitors the supply current to the electric motor.

1 . An electric motor drive for driving an alternating-current motor comprising: 
 a frequency converter for controlling the electric motor, wherein the frequency converter comprises a rectifier and an inverter;    an inductor unit, in a three-phase network, connecting the alternating-current power source to an input of the frequency converter to an input of the rectifier for reducing a surge current from a power source;    an intermediate circuit connecting an output of the rectifier and an input of the inverter for further reducing the surge current from the power source; and    a current measuring unit, in a three-phase network, measuring and/or monitoring a three-phase current to the electric motor.    
     
     
         2 . The electric motor drive according to  claim 1 , wherein the inverter, connected from the output of the rectifier, includes switching units and produces the three-phase current and a three-phase voltage to the electric motor.  
     
     
         3 . The electric motor drive according to  claim 1 , further comprising: 
 a current monitoring unit in a control unit of the inverter for supplying control pulses to a semiconductor switch in the switching units.    
     
     
         4 . The electric motor drive according to  claim 3 , wherein the switching units in the inverter comprises: 
 an auxiliary switch connected to the semiconductor switch which comprises a switching transistor that includes an emitter, base and collector.    
     
     
         5 . The electric motor drive according to  claim 3 , wherein the semiconductor switch is an insulated-gate bipolar transistor (IGBT).  
     
     
         6 . The electric motor drive according to  claim 4 , wherein the emitter of the switching transistor receives a voltage supply via a safety relay switch, when the safety relay switch is not actuated, where the voltage allows the switching transistor to be in a conducting state, 
 the base of the switching transistor receives the control pulses from the semiconductor switch, and    the collector, which is connected to ground, transmits undistorted control pulses to a control terminal of the semiconductor switch to supply current in the three-phase network to the electric motor.    
     
     
         7 . The electric motor drive according to  claim 1 , wherein the intermediate circuit comprises a capacitor connected at an output terminal of the rectifier.  
     
     
         8 . The electric motor drive according to  claim 7 , wherein the intermediate circuit comprises a switch arranged in series with the capacitor.  
     
     
         9 . The electric motor drive according to  claim 7 , wherein the capacitor has a value of 50 μF.  
     
     
         10 . A method for driving an alternating-current motor in an electric motor drive comprising: 
 controlling the electric motor in a frequency converter;    connecting the alternating-current power source to the input of an inductor in a three-phase network unit for reducing a surge current in a power source;    connecting a rectifier and inverter in the frequency converter for further reducing a surge current in the power source; and    measuring and/or monitoring a three-phase current to the electric motor.    
     
     
         11 . The method of  claim 10 , wherein the inverter, connected from an output of the rectifier, includes switching units and produces the three-phase current and a three-phase voltage to the electric motor.  
     
     
         12 . The method of  claim 10 , further comprising: 
 supplying control pulses to an IGBT semiconductor switch in the switching units.    
     
     
         13 . The method of  claim 11 , wherein the switching units in the inverter comprises: 
 an auxiliary switch connected to the semiconductor switch which comprises a switching transistor that includes an emitter, base and collector.    
     
     
         14 . The method of  claim 13 , wherein the emitter of the switching transistor receives a voltage supply via a safety relay switch, when the safety relay switch is not actuated, where the voltage allows the switching transistor to be in a conducting state, 
 the base of the switching transistor receives the control pulses from the semiconductor switch, and    the collector, which is connected to ground, transmits undistored control pulses to a control terminal of the IGBT semiconductor switch to supply current in the three-phase network to the electric motor.