System and method for servo control of nonlinear electromagnetic actuators

Abstract

Servo control using ferromagnetic core material and electrical windings is based on monitoring of winding currents and voltages and inference of magnetic flux, a force indication; and magnetic gap, a position indication. Third order nonlinear servo control is split into nested control loops: a fast nonlinear first-order inner loop causing flux to track a target by varying a voltage output; and a slower almost linear second-order outer loop causing magnetic gap to track a target by controlling the flux target of the inner loop. The inner loop uses efficient switching regulation, preferably based on controlled feedback instabilities, to control voltage output. The outer loop achieves damping and accurate convergence using proportional, time-integral, and time-derivative gain terms. The time-integral feedback may be based on measured and target solenoid drive currents, adjusting the magnetic gap for force balance at the target current. Incorporation of permanent magnet material permits the target current to be zero, achieving levitation with low power, including for a monorail deriving propulsion from the levitation magnets. Linear magnetic approximations lead to the simplest controller, but nonlinear analog computation in the log domain yields a better controller with relatively few parts. When servo-controlled solenoids provide actuation of a pump piston and valves, electronic LC resonance measurements determine liquid volume and gas bubble volume.

1 . A system for controlling movement of a solenoid having a drive coil, an armature capable of movement within the drive coil over a range of movement and a yoke coupled to the drive coil, the system comprising: 
 a controller that regulates the ongoing movement of the armature within the drive coil in response to a determination of present armature position, and in response to present armature position, provides an input to the drive coil that produces a desired rate of ongoing movement for a predetermined degree of armature position over the range of movement.    
   
   
       2 . The system as set forth in  claim 1  wherein the desired rate includes a rate that reduces impact of the armature with respect to a stop.  
   
   
       3 . The system as set forth in  claim 1  wherein the controller includes a position sensor that directly determines the present armature position free of estimation.  
   
   
       4 . The system as set forth in  claim 3  wherein the position sensor is constructed and arranged to directly determine the present armature position.  
   
   
       5 . The system as set forth in  claim 4  wherein the position sensor comprises a field effect device.  
   
   
       6 . The system as set forth in  claim 5  wherein the field effect device comprises a Hall effect sensor.  
   
   
       7 . The system as set forth in  claim 1  wherein the controller includes a position estimator that determines the present armature position based upon an estimation in response to signals from the drive coil.  
   
   
       8 . The system as set forth in  claim 7  wherein the estimation is based upon a measured magnetic flux of the drive coil.  
   
   
       9 . The system as set forth in  claim 8  wherein the position estimator includes a sense coil coupled to the drive coil that measures the magnetic flux.  
   
   
       10 . The system as set forth in  claim 9  wherein the position estimator is constructed and arranged to measure a current in the drive coil.  
   
   
       11 . The system as set forth in  claim 10  wherein the position estimator is constructed and arranged to determine the estimation based upon an approximate ratio of the current with respect to the magnetic flux.  
   
   
       12 . The system as set forth in  claim 7  wherein the estimation is based upon an oscillatory slope of a current in the drive coil.  
   
   
       13 . The system as set forth in  claim 12  wherein the controller is constructed and arrange to control a current in the drive coil in response to a ratio of the current versus the oscillatory slope so as to vary the current as a function of the oscillatory slope.  
   
   
       14 . The system as set forth in  claim 13  wherein the controller includes an amplifier that controls the current in the drive coil.  
   
   
       15 . The system as set forth in  claim 7  wherein the estimation is based upon a state observer that uses direct measurements of inputs and outputs of predetermined components of the system to estimate states of the system, the states including armature position.  
   
   
       16 . The system as set forth in  claim 7  wherein the estimation is based upon direct measurements of predetermined components of the system to estimate states of the system.  
   
   
       17 . The system as set forth in  claim 1  wherein the armature is adapted to operate an automotive valve.  
   
   
       18 . The system as set forth in  claim 17  wherein the armature is operatively connected to a biasing spring adapted to maintain the automotive valve in an opened position until driven closed in response to current applied by the controller.  
   
   
       19 . The system as set forth in  claim 18  wherein the controller is constructed and arranged to respond to changes in speed and power induced in an automotive engine.  
   
   
       20 . The system as set forth in  claim 19  wherein the desired rate includes a rate that reduces impact of the armature with respect to a stop.  
   
   
       21 . A method for controlling movement of a solenoid having a drive coil, an armature capable of movement within the drive coil over a range of movement and a yoke coupled to the drive coil, the method comprising the steps of: 
 regulating the ongoing movement of the armature within the drive coil in response to a determination of present armature position; and    in response to present armature position, providing an input to the drive coil that produces a desired rate of ongoing movement for a predetermined degree of armature position over the range of movement.