Abstract:
A current control system including a load, a power source in selective communication with the load and an energy management regulator adapted to receive electrical energy from the load and transfer the electrical energy to the power source.

Description:
[0001]     This application claims priority from U.S. Ser. No. 60/682,784 filed on May 19, 2005, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     Electromagnetic actuators typically include a coil and a controller for controlling the amount of electric current passing through the coil. The current passing through the coil may generate a magnetic flux and the magnetic flux may be proportional to the amount of force generated by the actuator. Therefore, the force generated by an actuator may be controlled by controlling the current passing through the coil, which in turn may be a function of the applied voltage.  
         [0003]     Typically, steady state current is controlled using pulse width modulation (“PWM”) techniques. Referring to  FIG. 1 , a typical PWM control system, generally designated  10 , may include a power source  12 , a controller  14 , a power switch  16  (e.g., a MOSFET switch), a diode  18  and a load  20 . The load  20  may consist of an inductive component  22  and a resistive component  24 . The power source  12 , diode  18  and load  20  each may be connected to ground  26  (e.g., a vehicle chassis).  
         [0004]     Accordingly, when the controller  14  actuates the switch  16 , current passes from the power source  12 , through the switch  16 , through the load  20  and back to the power source  12  by way of the ground  26 , thereby increasing the current in the load  20  at a positive rate. However, when the switch  16  is de-actuated, current in the inductive component  22  of the load  20  will pass through the resistive component  24 , through the diode  18  by way of the ground  26  and back to the inductive component  22 , thereby decreasing the current in the load  20  at a negative rate.  
         [0005]     As the current in the load  20  decreases, energy is dissipated from the diode  18  as heat, thereby increasing the power consumption of the system  10  and increasing the temperature of the associated controller assembly.  
         [0006]     Accordingly, there is a need for a current control system capable of recovering energy and returning the recovered energy to the power source, thereby facilitating a rapid reduction of current in the load. There is also a need for a current control system capable of operating at high frequencies without detriment to the performance of the system  
       SUMMARY  
       [0007]     In one aspect, a current control system may include a load, a power source in selective communication with the load and an energy management regulator adapted to receive electrical energy from the load and transfer the electrical energy to the power source.  
         [0008]     In another aspect, a current control system may include a load in electrical communication with a power source by way of a power switch, a high frequency controller adapted to control the actuation of the power switch and a low pass filter system disposed between the power switch and the load.  
         [0009]     In another aspect, a method for controlling a current passing through a load may include the steps of electrically connecting the load to a power source, thereby supplying energy to the load, disconnecting the load from the power source, after the disconnecting step, transferring at least a portion of the energy in the load to a capacitor, and, upon reaching a predetermined voltage across the capacitor, transferring at least a portion of the energy from the capacitor to the power source.  
         [0010]     Other aspects of the disclosed current control system will become apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a schematic illustration of a prior art control system for an electromechanical actuator;  
         [0012]      FIG. 2  is a schematic illustration of one aspect of the disclosed current control system;  
         [0013]      FIG. 3  is a schematic illustration of an alternative aspect of the current control system of  FIG. 2 ;  
         [0014]      FIG. 4  is a schematic illustration of a second aspect of the disclosed current control system; and  
         [0015]      FIG. 5  is a schematic illustration of a third aspect of the disclosed current control system. 
     
    
     DETAILED DESCRIPTION  
       [0016]     As shown in  FIG. 2 , one aspect of the disclosed current control system, generally designated  100 , may include a power source  102 , a controller  104 , a power switch  106 , a diode  108 , a load  110  and an energy management regulator  112 . The power source  102  may be a battery or the like, the controller  104  may be PWM controller or the like, the power switch  106  may be a MOSFET switch or the like and the diode  108  may be a free wheeling diode or the like. The load  110  may be the coil of an electromagnetic actuator (not shown) or the like and may include an inductive component  114  and a resistive component  116 . Additional loads or output drives  118 ,  120  may also be provided. The regulator  112  may include a capacitor  122 , an inductor  124 , a diode  126 , a controller  128  and a power switch  130 . Controllers  104  and  128  may be separate units or may be associated with a single processor or control unit.  
         [0017]     The power source  102 , the load  110  and the regulator  112  may be connected to ground  132 , such as a vehicle chassis or the like.  
         [0018]     The controller  104  may control the power switch  106  to achieve the desired current flow through the load  100 . In particular, when the controller  104  actuates the switch  106 , current may flow from the power source  102 , through the switch  106 , through the load  110  and back to the power source  102  by way of the ground  132 . However, when the switch  106  is de-actuated, the current in the inductive component  114  of the load  110  may flow through the resistive component  116  of the load  110 , to the capacitor  122  by way of the ground  132 , then through the diode  108  and back to the inductive component  114 . As the current passes through the capacitor  122 , the current may charge the capacitor  122 , thereby storing energy in the capacitor  122  as a voltage across the capacitor  122 .  
         [0019]     The voltage V Lload  across the inductive component  114  of the load  110  may be represented as follows: 
 
V Lload =I load R load +V D +V C    (Eq. 1) 
 
 wherein I load  is the load current, R load  is the resistance of the resistive component  116 , V D  is the voltage across the diode  108  and V C  is the voltage across the capacitor  122 . Therefore, as the voltage V C  across the capacitor increases, the load current I load  may decrease a corresponding amount. 
 
         [0020]     Thus, the capacitor  122  of the regulator  112  may facilitate a faster reduction of load current, thereby facilitating a more robust control response.  
         [0021]     As the voltage across the capacitor  122  increases, the controller  128  may determine that a threshold voltage across the capacitor  122  has been reached and may actuate the power switch  130  of the regulator  112  to facilitate the removal of stored energy, thereby reducing the risk of damage to the components of the system  100 . In particular, the controller  128  may actuate switch  130  such that current may flow from the capacitor  122 , through the inductor  124  and the switch  130  and back to the capacitor  122 . However, when the switch  130  is de-actuated, the current in the inductor  124  may flow through the diode  126  and the power source  102  and back to the inductor  124  by way of the ground  132 .  
         [0022]     Thus, the energy removed from the load  110  when the switch  106  is de-actuated may be recovered and returned to the power source  102  by way of the regulator  112 .  
         [0023]     As shown in  FIG. 3 , an alternative aspect of the disclosed current control system, generally designated  200 , may be adapted for bidirectional current flow and may include a power source  202 , a controller  204 , a first power switch  206 , a second power switch  208 , a load  210  and an energy management regulator  212 . The load  110  may be the coil of an electromagnetic actuator (not shown) or the like and may include an inductive component  214  and a resistive component  216 . The regulator  212  may include a capacitor  218 , an inductor  220 , a third power switch  222 , a fourth power switch  224  and a controller  226 . The power switches  206 ,  208 ,  222 ,  224  may include body diodes  228 A,  228 B,  228 C,  228 D.  
         [0024]     The power source  202 , the load  210  and the regulator  212  may be connected to ground  230 , such as a vehicle chassis or the like.  
         [0025]     Thus, when switch  206  is actuated, current may flow (e.g., positive current flow) from the power source  202 , through the switch  206  and the load  210  and back to the power source  202  by way of the ground  230 . When the switch  206  is de-actuated, current may flow from the load  210 , to the capacitor  218  by way of the ground  230 , through the diode  228 B of the switch  208  and back to the load  210 , thereby accumulating a voltage across the capacitor  218  such that the node −V source  becomes more negative.  
         [0026]     When the controller  226  of the regulator  212  determines that the voltage across the capacitor  218  has reached and/or exceeded a predetermined threshold value, the switch  222  may be actuated such that current may flow from the capacitor  218 , through the inductor  220  and back to the capacitor  218  by way of the switch  222 . When the switch  222  is de-actuated, the current may flow from the inductor  220 , through the diode  228 C of the switch  224 , to the power source  202  and back to the inductor  220  by way of the ground  230 , thereby returning energy recovered by the regulator  212  to the power source  202 .  
         [0027]     An opposite current flow may be achieved by actuating switch  208  such that current may flow from the capacitor  218 , through the load  210  by way of the ground  230 , through the switch  208  and back to the capacitor  218  by way of the node −V source , thereby decreasing the voltage across the capacitor  218 . When switch  208  is de-actuated, the current may flow from the load  210 , through the diode  228 A of the switch  206 , through the power source  202  and back to the load  210  by way of the ground  230 .  
         [0028]     The switch  224  may be actuated such that current may flow from the power source  202 , through the switch  224  and the inductor  220  and back to the power source  202  by way of the ground  230 . When the switch  224  is de-actuated, current may flow from the inductor  220 , through the capacitor  218  and the diode  228 D of the switch  222  and back to the inductor  220 , thereby accumulating a voltage across the capacitor  218 .  
         [0029]     Thus, the voltage of the node −V source  may be controlled by controlling the actuation and de-actuation of switches  206 ,  208 ,  222 ,  224 , which may facilitate the recovery and return of electrical energy to the power source  202 , while facilitating bidirectional current flow.  
         [0030]     As shown in  FIG. 4 , another aspect of the disclosed current control system, generally designated  300 , may include a power source  302 , a controller  304 , a power switch  306 , a diode  308 , a low pass filter system  310 , a current feedback system  312  and a load  314 . The power source  302 , diode  308  and load  314  may be connected to ground  324 .  
         [0031]     The current feedback system  312  may include a sense resistor  320  and an amplifier  322 , such as a differential amplifier or the like. The amplifier  322  may detect a voltage drop across the resistor  320  and may communicate a corresponding current signal to the controller  304  (e.g., by way of communication line  326 ). Therefore, the controller  304  may generate a control signal for controlling the switch  306  based upon an input command  328  and current feedback  326  from the current feedback system  312 . In one aspect, the controller  304  may operate at high frequencies, such as about 50 to about 150 kHz, for example.  
         [0032]     The low pass filter system  310  may include an inductor  316  and a capacitor  318  and may be adapted to filter high frequency signals. In one aspect, the low pass filter system  310  may reduce the bandwidth of the signals that reach the sense resistor  320  and ultimately the load  314 . For example, filtered signals may have a frequency of about 0 to about 5 kHz.  
         [0033]     Thus, by incorporating the low pass filter  310 , the controller  304  may be a high frequency controller (e.g., a high frequency PWM controller) and may control the switch  306  at a high frequency without some or all of the disadvantages (e.g., EMC problems) associated with a high frequency signal passing through the wire harness  315 , which may be relatively long, to the load  314 .  
         [0034]     Referring to  FIG. 5 , an alternative aspect of the current control system illustrated in  FIG. 3 , generally designated  400 , may include a power source  402 , a controller  404 , a first power switch  406 , a second power switch  408 , a load  410 , an energy management regulator  412 , a low pass filter system  414  and a current feedback system  416 .  
         [0035]     Thus, the system  400  may achieve bidirectional current flow, as described above, in response to an input signal  418  and a current feedback signal  420  from the current feedback system  416 . Furthermore, the energy management regulator may facilitate the recovery and return of electrical energy to the power supply. Still furthermore, with the addition of the low pass filter system  414 , the controller  404  may operate the switches  406 ,  408  at a high frequency without negative downstream effects.  
         [0036]     Although various aspects of the disclosed current control system have been shown and described, modifications may occur to those skilled in the art upon reading the specification. This application includes such modifications and is limited only by the scope of the claims.