Abstract:
This invention utilizes the power electronics of a switched reluctance motor controller and the phase windings of a switched reluctance motor to make up a single stage boost converter capable of charging a battery with power factor correction (PFC) in the AC line.

Description:
BACKGROUND 
     The present disclosure relates to generating a battery charge current for a hybrid electric vehicle with multi-phase motor drive circuits. More particularly, this invention utilizes a switched reluctance motor controller to both drive a switched reluctance motor and to implement the converter circuits of a battery charger. 
     It is known to those skilled in the art that battery charging circuits and motor drive circuits have many parts in common. Various methods of combining a battery charger and a motor drive controller to eliminate redundant components and thereby reduce cost and weight are utilized in the art. Each of the known methods requires additional components beyond the motor control electronics to implement the battery charging function. 
     In a typical battery charger, an AC input is rectified to produce a DC voltage. Often, a second stage DC converter is also utilized to produce the correct charging voltage for the battery. In this arrangement, the AC line current has large peaks that reduce the power factor (the ratio of real power to apparent power). This limits the amount of power that can be drawn from the AC input. The AC input currents can be forced to a unity power factor by employing a boost circuit. 
     SUMMARY 
     Disclosed is a battery charging circuit which incorporates two or more semiconductor H-bridges with the windings of an electromagnetic machine connected across the H-bridges and each line of an AC electric source connected to a switching node of the H-bridge. In this way, the elements of an electric motor control circuit are also used for the battery charging circuits and can be controlled to draw power factor corrected currents from the AC source. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates two linked single stage boost converters. 
         FIG. 2  illustrates a three phase power factor correction (PFC) boost converter. 
         FIG. 3  illustrates an SR motor/motor controller configured to use a leakage inductance to provide power factor correction. 
         FIG. 4  illustrates an asymmetrical H-bridge. 
         FIG. 5  illustrates a three phase SR motor connected to three asymmetrical H-bridges, and a three phase AC source. 
         FIG. 6  illustrates a three phase SR motor connected to three asymmetrical H-bridges, and a single phase AC source. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates two linked single stage boost converters  20 ,  22 , one to each side of an AC line  30 . Inductor  51 , diode  52 , and transistor  53  form a boost converter circuit  20  attached to a power side of the AC line  30  and inductor  61 , diode  62 , and transistor  63  form the boost converter  22  attached to a neutral side of the AC line  30 . When the power side of the AC line  30  is positive with respect to neutral, the first boost converter  20  operates in a power factor correction (PFC) mode in order to produce a battery charging current. When the AC line  30  is negative with respect to neutral, the second boost converter  22  is switched according to known PFC techniques, thereby producing a battery charging current. A controller  40  senses the line voltage, at least one line current and the battery voltage in order to allow for the implementation of the PFC charging function. A line filter  50  is used to filter the switching frequencies from the AC line  30 . The methods and techniques for performing this operation are understood in the art. 
       FIG. 2  shows a three phase PFC boost converter system  100  incorporating a multiple boost converter. Each line of the AC source  120  has an inductor  150 ,  152 ,  154 , a low side switch  160 ,  162 ,  164  and a high side switch  170 ,  172 ,  174  forming one boost circuit per phase. Each of the high side switches  170 ,  172 ,  174 , and the low side switches  160 ,  162 ,  164  is a semi-conductor switch. The set of six switches  160 ,  162 ,  164 ,  170 ,  172 ,  174  form a three phase inverter that drives a three phase motor according to known techniques. There are several methods of switching the three phase inverter  100  in order to produce three phase power factor correction while generating a battery charging current. At least two line currents  132 ,  134 , a line voltage  136  and the battery voltage  138  are sensed by a controller  140  in order to properly effect the power factor correction. 
     Multiphase AC motors have a leakage inductance and the leakage inductance can be used to implement the inductors of a three phase PFC battery charging circuit.  FIG. 3  illustrates a system implementing this feature. An AC line  230  is rectified through a diode bridge  232  to form an intermediate unregulated DC voltage  234 . The unregulated DC voltage  234 , the phase windings  240 ,  242 , the switch  264 , and the diode corresponding to transistor  261 , form a boost circuit (as in  FIG. 1 ) that functions as a PFC battery charging circuit. Alternatively, phase windings  240  and  244 , switch  266  and the diode corresponding to transistor  261  can implement the boost function. The diode bridge  232  adds components that can add cost and space to the overall inverter/battery charger combination. 
     Switched reluctance (SR) motors are in a class of multiphase motors in which the phase windings are often not interconnected. The power switching structure used to drive an SR motor also differs from the standard three phase bridge employed with other poly-phase motors.  FIG. 4  illustrates an asymmetrical H-bridge  300  used to drive each phase of a SR motor. In the H-bridge  300 , an insulated gate bipolar transistor (IGBT)  351  is connected to a positive side  310  of a DC voltage  312  and is called the high side switch. An IGBT  362  is connected to a negative or return side  314  of the DC voltage  312  and is called the low side switch. Both the high side  310  and low side  314  IGBTs  351 ,  352  can be varied types of transistor, depending on the application. Diodes  361  and  362  are used for ‘free-wheeling’ operation during active current control. Diodes  363  and  364  provide a ‘hard chopping’ and quick discharge of phase energy back to the DC source  312 . Collectively, transistor  351 , diode  361 , and diode  363  are a high side leg  320 , while transistor  352 , diode  362 , and diode  364  are a low side leg  330 . The center point  322 ,  332  of each leg, where the phase winding connects to each leg, is called a switching node  322 ,  332 . One current sensor  340  per phase is used for motor operation. 
       FIG. 5  illustrates a three phase SR motor  410  connected to three asymmetrical H-bridges  422 ,  424 ,  426 . This connection of three asymmetrical H-bridges  422 ,  424 ,  426 , a three phase motor  410 , a DC voltage source  430 , a bus capacitor  432 , current sensors  440 ,  442 ,  444 , and a bus voltage sensor  446  forms a SR motor controller  400 . 
     To implement a battery charging circuit using the motor controller  400 , each leg  452 ,  454 ,  456  of a three phase AC line  450  is connected to the switching node  462 ,  464 ,  466  of each corresponding high side leg. Thus the low side leg of each H-bridge  422 ,  424 ,  426  functions as a boost converter using the SR motor phase  412 ,  414 ,  416  as the boost inductor. 
     Described below is an example operation with the three phase source  450  having a positive phase output  452 , and two negative phase outputs  454 ,  456 . When the low side IGBT  482  is on, energy is stored in the magnetic field of the motor phase  412 . When the low side IGBT  482  is switched off, the boost function current flows through a diode  492 , the battery  430 , diodes  493  and  495  and to the AC source  450 . This switching is implemented using known PFC methods in all three asymmetrical H-bridges  422 ,  424 ,  426  to create sinusoidal currents in the AC lines  452 ,  454 ,  456  in phase with the line voltages. The phase current sensors  440 ,  442 ,  444  provide a line current feedback to a controller  470 . The battery voltage sensor  446  is additionally part of the SR motor controller  470 . A phase voltage sensor  472  is added to match the phase of the line currents  440 ,  442 ,  444  to the line voltages. Otherwise a SR motor controller with this configuration includes all motor controlling and battery charging circuits. As on all AC lines attached to high frequency switching circuits, a line filter  474  is included. 
     Any voltage can be used to generate the charging current, provided the peak phase to phase voltage is less than the battery voltage, however, a single phase 110 or 220 volt outlet is the most prevalent.  FIG. 6  illustrates a single phase connection for implementing the PFC battery charging circuit described above with regard to  FIG. 5 . As in  FIG. 1 , when the AC line  530  is positive, the low side leg of phase one  520  functions as a boost converter. When a low side switch  582  is on, current flows from the AC line  530 , through the phase winding  512 , returning to the neutral side of the AC line  530  through diode  593 , and stores energy in the magnetic field of the phase winding  512 . When the low side switch  582  is switched off, the magnetic field in the phase winding collapses, thereby producing a voltage that is added to the AC line voltage  530  and forward biases diode  592 . Current then flows through the battery  550  and again returns to the neutral side of the AC line  530  through diode  593 . The high side leg is not conducting current because a high side switch  581  is off and a diode  591  is reverse biased. 
     When the AC line goes negative, phase legs  1  and  4  are utilized. When the low side switch  584  is on, current flows through phase two  522  with diode  591  providing the return path. Then, when the low side switch  584  is switched off, flyback current flows through a diode  594 , the battery  550  and returns through a diode  591  to the AC line  530 . 
     The single phase connection illustrated in  FIG. 6  of the SR bridge includes the components necessary to implement both the motor control function as well as the battery charging circuits. As in the three phase case, a line voltage sensor  560  and AC line filter  562  are further included. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this disclosure.