Variable frequency drive system

Abstract

A motor drive system for a linear motor having a plurality of stator segments and a rotor movable relative to the plurality of stator segments. The motor drive system includes a variable frequency drive comprising at least one energy cell, the variable frequency drive supplying a medium voltage between 1 kV and 100 kV and a plurality of switches operable to connect the variable frequency drive to selected segments of the plurality of stator segments based upon a position of the rotor. The variable frequency drive is connectable to an external energy source to at least one of charge the at least one energy cell or to supply power to the external energy source.

What is claimed is: 
     
         1 . A motor drive system for a linear motor having a plurality of stator segments and a rotor movable relative to the plurality of stator segments, the motor drive system comprising:
 a variable frequency drive comprising at least one energy cell, the variable frequency drive supplying a medium voltage between 1 kV and 100 kV; and   a plurality of switches operable to connect the variable frequency drive to selected segments of the plurality of stator segments based upon a position of the rotor,   wherein the variable frequency drive is connectable to an external energy source to at least one of charge the at least one energy cell or to supply power to the external energy source.   
     
     
         2 . The motor drive system according to  claim 1 , wherein the at least one energy cell comprises at least one low-voltage energy storage module. 
     
     
         3 . The motor drive system according to  claim 2 , wherein the at least one low-voltage energy storage module comprises at least one of an ultracapacitor or a flywheel. 
     
     
         4 . The motor drive system according to  claim 2 , wherein the at least one energy cell further comprises a converter to convert a voltage supplied by the at least one low-voltage storage module to the medium voltage supplied by the variable frequency drive. 
     
     
         5 . The motor drive system according to  claim 4 , wherein the converter reduces a voltage supplied from the external energy source to the variable frequency drive. 
     
     
         6 . The motor drive system according to  claim 4 , wherein the voltage supplied from the at least one low-voltage storage module to the converter is one of single phase or multiphase. 
     
     
         7 . The motor drive system according to  claim 4 , wherein the at least one low-voltage storage module comprises at least two low-voltage storage modules connected to the converter. 
     
     
         8 . The motor drive system according to  claim 7 , wherein the at least two low-voltage storage modules are arranged in parallel and connected to a common bus, and
 wherein the converter is connected to the at least two low-voltage storage modules via the common bus.   
     
     
         9 . The motor drive system according to  claim 8 , further comprising an inductor arranged to couple the common bus to the converter. 
     
     
         10 . The motor drive system according to  claim 4 , wherein the at least one low-voltage storage module comprises a flywheel and a motor, and
 wherein the motor is coupled to the converter.   
     
     
         11 . The motor drive system according to  claim 10 , wherein the motor is a multiphase motor and each phase is connected to the converter. 
     
     
         12 . A linear motor system, comprising:
 a plurality of line commutated inverters distributed along a linear motor and each of the plurality of line commutated inverters having an alternating current side that outputs alternating current, and a direct current side that conveys direct current,   wherein the alternating current side of each line commutated inverter is connected to a stator segment of the linear motor, and   wherein the direct current side of each line commutated inverter are connected in series.   
     
     
         13 . The linear motor system of  claim 12 ,
 wherein the direct current sides of the line commutated inverters are connected in series to line commutated inverters that connect to an energy storage module and to an energy source.   
     
     
         14 . The linear motor system of  claim 13 ,
 wherein the energy storage module comprises at least one of an ultracapacitor and a flywheel.   
     
     
         15 . The linear motor system of  claim 13 ,
 wherein a direct current in a direct current loop smoothing inductor is built up by converting energy either from the energy source or from the energy storage module via a respective line commutated inverter connected to the energy source or the energy storage.   
     
     
         16 . The linear motor system of  claim 15 ,
 wherein the built up direct current is used to charge or discharge the energy storage module via the line commutated inverter connected to the energy storage.   
     
     
         17 . The linear motor system of  claim 16 ,
 wherein, as a rotor travels along the linear motor, the line commutated inverters connected to stator segments of the linear motor commutate the direct current sequentially into each phase of stator coils in the stator segments in order to form a moving flux that drives the rotor.   
     
     
         18 . The linear motor system of  claim 17 ,
 wherein the line commutated inverters connected to stator segments which are not currently powered bypass the direct current by turning on a plurality of thyristors in one or more phases.   
     
     
         19 . The linear motor system of  claim 18 ,
 wherein a direct current inductor is implemented using passive stator coils that are not currently powered, and selected thyristors are activated such that passive stator coils are connected in the direct current loop to provide direct current inductance.   
     
     
         20 . The linear motor system of  claim 12 ,
 wherein the distributed line commutated inverters are connected to the linear motor to reduce torque ripples,   wherein each of the distributed line commutated inverters have multiple phase legs, and   wherein adjacent line commutated inverters operate with phase shifts.   
     
     
         21 . The linear motor system of  claim 12 ,
 wherein the linear motor is arranged along a guideway, over which a pod is driven electromagnetically as a rotor.