Abstract:
A power supply generates alternating current and direct current from a constant-voltage source. A multi-phase pulse width modulation voltage source inverter is connected across the source to output multi-phase alternating current. At least one waveform generator is bridged in parallel with the inverter, with each waveform generator outputting zero-sequence waveform current compensated to maintain the multi-phase current within a predetermined tolerance from a desired set point. A rectifier receives the waveform current and generates direct current.

Description:
FIELD OF THE INVENTION 
     The present invention relates to power supplies, and more particularly to power supplies for vehicles. 
     BACKGROUND OF THE INVENTION 
     Vehicles may require a voltage source that provides a regulated voltage such as 12 VDC and/or 48 VDC. Internal combustion engine (ICE) vehicles use alternators that generate AC voltage, which is rectified to DC voltage. When the ICE is either operated intermittently (in a hybrid vehicle) or is absent (in a fuel cell or battery powered vehicle), an alternator can no longer be used to generate auxiliary DC power. DC power from a battery or fuel cell is the normal source of power for electric traction motors in such vehicles. DC/DC converters that are supplied by a high voltage DC bus are typically used to provide auxiliary power at a lower voltage level. 
     The reliability of DC/DC converters supplied by the high voltage bus needs to improve for automotive applications. DC/DC converters are also relatively expensive, especially when structurally enhanced to meet the tougher automotive applications. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a power supply that generates low voltage direct current (DC) from a high voltage DC voltage source. The power supply includes an inverter that supplies multi-phase current to a traction motor. A controller determines an adjusted first phase current based in part on the measured first phase current and determines an adjusted second phase current based in part on the measured second phase current. The controller calculates an available current based on the first and second adjusted phase currents and generates a voltage control PWM signal based on the available current. 
     In one feature, the power supply further includes a first auxiliary transformer supplied with a first auxiliary current from the inverter and having a first voltage output and a second auxiliary transformer supplied with a second auxiliary current from the inverter and having a second voltage output. The controller determines the first and second adjusted phase currents based on the first and second auxiliary currents. 
     In another feature, the controller controls the inverter based on the voltage control signal. 
     In another feature, the adjusted first phase current is determined by subtracting a first phase magnetizing current and a total auxiliary current from the measured first phase current. The first magnetizing current is determined based on the first phase voltage and frequency. 
     In still another feature, the adjusted second phase current is determined by subtracting a second phase magnetizing current and a total auxiliary current from the measured second phase current. The second magnetizing current is determined based on the second phase voltage and frequency. 
     In yet another feature, the inverter includes a first phase half bridge connected across the DC voltage source to provide the first phase current. A second phase half bridge is connected across the DC voltage source to provide the second phase current. A third phase half bridge connected across the DC voltage source to provide a third phase current to the traction motor. The inverter further includes a first auxiliary half bridge connected across the DC voltage source to provide a first auxiliary current and a second auxiliary half bridge connected across the DC voltage source to provide a second auxiliary current. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is an electrical schematic of a power supply with 2 dual-switch auxiliary power half-bridges according to the present invention; 
         FIG. 2  is an electrical schematic of an exemplary configuration of the power supply with 2 single-switch auxiliary power half-bridges according to the present invention; 
         FIG. 3  is an electrical schematic of an alternate configuration of the power supply with 2 single-switch auxiliary power half-bridges according to the present invention; and 
         FIG. 4  is a functional block diagram of a controller for the electrical circuits of  FIGS. 1–3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. 
     In overview, the power system according to the present invention produces AC power for an electric traction motor as well as auxiliary low voltage DC power. DC power is preferably output at a first voltage level such as 12 volts nominal and also at a second voltage level such as 42 volts nominal. A three-phase inverter generates power that is output to traction motor windings. One half-bridge is added to the three-phase traction inverter for each auxiliary voltage level that is produced. A controller operates the inverter and auxiliary bridge(s) to ensure that traction power demand takes precedence over auxiliary power demand. Accordingly, the controller limits the auxiliary power so as to maintain the multi-phase AC current to the traction motor within a predetermined tolerance. 
     The controller includes a traction inverter control module that calculates an available current signal, which is output to an auxiliary voltage control module. Available current is defined as the difference between the maximum safe current of a traction inverter switch and the measured value of a traction phase current. The auxiliary voltage control module adjusts an output thereof to maintain an auxiliary current less than the available current signal. 
     Three alternative power conversion systems are shown in  FIGS. 1 through 3 . A controller, further described in the discussion of  FIG. 4 , measures one or more parameters and operates the power conversion systems. Referring now to  FIG. 1 , a power supply  100  includes a DC voltage source  104  and a 3-phase inverter  108 . First, second and third primary half-bridges  112 -A,  112 -B and  112 -C of the inverter  108  are associated with phases A, B, and C. The half-bridges  112 -A,  112 -B and  112 -C include first and second switches SA 1  and SA 2 , SB 1  and SB 2 , and SC 1  and SC 2 , respectively, that are connected across the voltage source  104 . The switches SA 1 , SA 2 , SB 1 , SB 2 , SC 1  and SC 2  are also connected in anti parallel with diodes DA 1 , DA 2 , DB 1 , DB 2 , DC 1  and DC 2 , respectively. 
     Output conductors  116 A,  116 B and  116 C have one end that is connected between the switches SA 1 , SA 2 , SB 1 , SB 2 , SC 1  and SC 2 , respectively. Opposite ends of the conductors  116 A,  116 B,  116 C are connected to first ends of first, second and third primary windings  120 - 1 ,  120 - 2 , and  120 - 3  of a first transformer  124 . Opposite ends of the conductors  116 A,  116 B,  116 C are also connected to first ends of first, second and third primary windings  128 - 1 ,  128 - 2 , and  128 - 3  of a second transformer  132  and to windings of a traction motor  134 . First and second auxiliary half-bridges  112 -D and  112 -E also include switches SD 1 , SD 2 , SE 1  and SE 2 , respectively, that are connected across the voltage source  104 . The switches SD 1 , SD 2 , SE 1  and SE 2  are also connected in anti parallel with diodes DD 1 , DD 2 , DE 1  and DE 2 , respectively. The first and second auxiliary half-bridges  112 -D and  112 -E are associated with the generation of first and second auxiliary voltage levels, as will be described further below. 
     Output conductor  116 -D has one end that is connected between the switches SD 1  and SD 2 . An opposite end of the conductor  116 -D is connected to second ends of the first, second and third primary windings  120 - 1 ,  120 - 2 , and  120 - 3  of the first transformer  124 . Output conductor  116 -E has one end that is connected between the switches SE 1  and SE 2 . An opposite end of the conductor  116 -E is connected to second ends of the first, second and third primary windings  128 - 1 ,  128 - 2 , and  128 - 3 , respectively, of the second transformer  132 . 
     A rectifier  144  includes first, second, third and fourth diodes  150 - 1 ,  150 - 2 ,  150 - 3  and  150 - 4 , respectively. The anode of diode  150 - 2  is connected to the cathode of diode  150 - 1 . The anode of diode  150 - 3  is connected to the cathode of diode  150 - 4 . The anode of diode  150 - 4  is connected to the anode of diode  150 - 1 . The cathode of diode  150 - 2  is connected to the cathode of diode  150 - 3 . 
     Secondary windings  160 - 1 ,  160 - 2  and  160 - 3  of the first transformer  124  are connected in series. One end of the third secondary winding  160 - 3  is connected to the cathode of diode  150 - 1  of the rectifier  144 . One end of the first secondary winding  160 - 1  is connected to the anode of the diode  150 - 3  of the rectifier  144 . A capacitor  164  has one end that is connected to the anode of diode  150 - 4  and an opposite end that is connected to the cathode of diode  150 - 3 . In a similar manner, secondary windings  180 - 1 ,  180 - 2  and  180 - 3  of the second transformer  132  are connected to a rectifier  184  and a capacitor  188 . Current sensors  190 -A,  190 -B,  190 -D and  190 -E sense current flowing through the conductors  116 -A,  116 -B,  116 -D and  116 -E. Voltage sensor  192 -D senses voltage across capacitor  164  and voltage sensor  192 -E senses voltage across capacitor  188 . 
     In one embodiment, the transformers  124  and  132  are integrated into corners of traction motor  134 . In an alternative embodiment, the transformers  124  and  132  are free standing. In one embodiment, magnetics associated with each power converter are located in corners of the traction motor stator. In this regard, laminations are cut in a square configuration instead of in a traditional circular configuration. 
     Windings of the traction motor  134  respond to plus and minus sequence voltage from inverter  108 . Windings of the traction motor  134  preferably do not respond to zero-sequence waveform voltages from half-bridges  112 -D and  112 -E in conductors  116 -D and  116 -E. Series-connected secondary windings of each of three-phase auxiliary power transformers  124  and  132  do not produce an output in response to the plus- and minus-sequences of the inverter  108 . These secondary windings do produce an output in response to the zero-sequence waveform voltages that are generated from auxiliary half-bridges  112 -D and  112 -E. 
     A positive or negative sequence sine wave output from traction inverter  108  produces torque in traction motor  134 . Zero sequence sine wave waveform current from each auxiliary half-bridge  112 -E and  112 -D produce a corresponding DC auxiliary voltage at the output of rectifiers  144  and  184 . Current sensors  190 -D and  190 -E measure currents from corresponding auxiliary half-bridges  112 -D and  112 -E. A controller bases control commands on the measured currents as described in further detail below in conjunction with  FIG. 4 . 
     As previously noted, the auxiliary half-bridges  112 -D and  112 -E include switches SD 1 , SD 2 , SE 1  and SE 2 , respectively, with anti-parallel free-wheeling diodes DD 1 , DD 2 , DE 1  and DE 2 , respectively. Alternatively, if the output of the auxiliary half-bridge is capacitor coupled, the upper leg of the auxiliary half-bridge only needs the free-wheeling diode and not the switch. This arrangement is shown in both  FIGS. 2 and 3 . 
     Referring now to  FIG. 2 , a power supply  200  having single-switch auxiliary power half-bridges is shown. Many elements of power supply  200  are the same as those of the power supply  100  in  FIG. 1 . However, the elements of the auxiliary half-bridges providing current to secondary windings of transformers  124  and  132  are different between power supply  200  and power supply  100 . 
     Power supply  200  replaces each half-bridge  116 -D and  116 -E of circuit  100  with half-bridges  205 -D and  205 -E. Half-bridge  205 -D has a diode DD 1  and a diode DD 2  connected in series across the voltage source  104 . A switch SD 2  is connected in parallel to diode DD 2 . The half-bridge  205 -E likewise includes diodes DE 1  and DE 2  and a switch SE 2  that are arranged in a similar manner. The half-bridge  205 -D is connected to one end of capacitors  220 ,  221 , and  222 . Opposite ends of the capacitors  220 ,  221  and  222  are connected to the primary windings  120 - 1 ,  120 - 2  and  120 - 3 , respectively. The half-bridge  205 -E is connected to the end of capacitors  224 ,  226 , and  228 . Opposite ends of the capacitors  224 ,  226  and  228  are connected to the primary windings  128 - 1 ,  128 - 2  and  128 - 3  of the transformer  132 . 
       FIG. 3  shows an alternate connection for the traction motor  134  in a power supply  300 . The power supply  300  includes many elements from the power supply  200 . The differences between the power supply  200  and the power supply  300  are in the relative positioning of inverter  108 , auxiliary transformers  124  and  132 , sensors  190 -A and  190 -B, and motor  134 . The power supply  200  ( FIG. 2 ) connects auxiliary transformers  124  and  132  and motor  134  to power phases  116 -A and  116 -B and  116 -C through sensors  190 -A and  190 -B. The power supply  300  ( FIG. 3 ) connects the power phases  116 -A,  116 -B and  116 -C of inverter  108  between auxiliary transformers  124  and  132  and motor  134 . The power supply  300  positions sensors  190 -A and  190 -B between inverter  108  and motor  134 . The impact of these differences will be further discussed in conjunction with the control module of  FIG. 4 . 
     Current sensors  190 -A and  190 -B generate measured phase currents IPHASEA and IPHASEB for phases A and B, respectively. Current sensors  190 -D and  190 -E generate zero-sequence waveform currents I 12 Vaux and I 42 Vaux that are produced by the zero-sequence waveform voltage from the auxiliary bridges  112 -D,  112 -E, respectively. The voltage sensors  192 -D and  192 -E generate voltage signals V 12 VAUX and V 42 VAUX that indicate the voltages supplied by the auxiliary transformers  124  and  132 , respectively. Voltage signals VAPPLIEDA and VAPPLIEDB indicate the commanded positive or negative sequence voltage applied to the traction motor for phases A and B, respectively. VAPPLIEDA and VAPPLIEDB also indicate the commanded positive or negative sequence voltage applied through the auxiliary transformers  124 , 132 . 
     For the power supplies  100 ,  200  and  300  discussed above, there are two components of current flowing in the transformer primary. A first current component includes a magnetizing current that results from the positive and negative sequence voltage. A second current component includes a reflected load current produced by the zero sequence voltage. 
     If the auxiliary transformers  124 ,  132  are connected after the traction current sensors, as is the case for the power supplies  100 ,  200  of  FIGS. 1 and 2 , respectively, the magnetizing current is sensed by the current sensors  190 -A and  190 -B. The magnetizing current represents an error in IPHASEA and IPHASEB and must be subtracted out to maintain accurate control of the traction current. The magnetizing current, however, is not sensed by the current sensors  190 -D,  190 -E. Therefore, the magnetizing current IMAGA and IMAGB for phases A and B, respectively, are estimated. IMAGA and IMAGB are estimated based on the following equations: 
                     I   MAGA     =       v   APPLIEDA         2   ⁢   π   ⁢           ⁢   f     ⁢                             I   MAGB     =       v   APPLIEDB         2   ⁢   π   ⁢           ⁢   f     ⁢                           
where f is the voltage frequency.
 
     Because all 3 secondary windings of each of the auxiliary transformers  124 ,  132  are in series, I 12 Vaux and I 42 Vaux also flow through the respective primary windings of the auxiliary transformer  124 ,  132 . As a result, I 12 Vaux and I 42 Vaux are also subtracted from IPHASEA and IPHASEB. Subtracting I 12 Vaux, I 42 Vaux, IMAGA and IMAGB provides adjusted currents IADJA and IADJB for phases A and B, respectively. 
     Referring now to  FIG. 4 , a control system  400  is illustrated and defines the control logic for the power supplies  100  and  200  (i.e., where the auxiliary transformers  124 ,  132  are connected after the traction current sensors  190 -A,  190 -B). The current sensors  190 -A,  190 -B,  190 -D, and  190 -E, voltage sensors  192 -D and  192 -E, and switches of the power supply circuits  100 ,  200 ,  300  are connected to the control system  400 . The control system  400  receives current signals and voltage signals from the connected power supply circuit and controls the switches SA 1 , SA 2 , SB 1 , SB 2 , SC 1 , SC 2 , SD 1 , SD 2 , SE 1 , and SE 2 . 
     The signals f, V 12 VAUX, V 42 VAUX, VAPPLIEDA, VAPPLIEDB, IPHASEA, IPHASEB, I 12 Vaux and I 42 Vaux are inputs to the control system  400 . V 12 VAUX, V 42 VAUX, I 12 Vaux and I 42 Vaux are input to a voltage control module  402 . The voltage control module  402  determines a pulse-width modulated (PWM) voltage control signal based on V 12 VAUX, V 42 VAUX, I 12 Vaux and I 42 Vaux and an available current signal IAVAILABLE to control the voltage of the auxiliary transformers  124 ,  132 . IAVAILABLE is the difference between the maximum current that the traction inverter switches can handle (a predetermined set point) and the measured value of the traction phase currents. The voltage control module  402  maintains the auxiliary current less than IAVAILABLE. I 12 Vaux and I 42 Vaux are summed by a summer  403  to provide a total auxiliary current IAUX. 
     VAPPLIEDA, VAPPLIEDB and f are input to magnetizing current estimators  404  and  406 . More specifically, the current estimator  404  determines IMAGA based on VAPPLIEDA and f as described above. Similarly, the current estimator  406  determines IMAGB based on VAPPLIEDB and f. IMAGA and IAUX are inverted and summed with IPHASEA by a summer  408  to provide an adjusted phase current IADJA. In effect, IMAGA and IAUX are subtracted from IPHASEA. Similarly, IMAGB and IAUX are inverted and summed with IPHASEB by a summer  410  to effectively subtract IMAGA and IAUX from IPHASEA to provide IADJB. 
     IADJA and IADJB are sent to a traction motor control module  412 . The traction motor control module  412  represents a typical AC control system such as a field oriented system. The traction motor control module  412  determines a PWM motor control signal based on IADJA and IADJB. The traction motor  134  is operated based on the PWM motor control signal. Traction power demand takes precedence over auxiliary power demand. To accomplish this, the traction motor control module  412  determines IAVAILABLE based on IADJA and IADJB. IAVAILABLE is input to the voltage control module, which limits the PWM voltage control signal such that the auxiliary power current is less than IAVAILABLE, as discussed above. 
     If the auxiliary transformers  124 ,  132  are connected before the traction current sensors  190 -A,  190 -B, as is the case for the power supplies  300  of  FIG. 3 , IMAGA, IMAGB and IAUX need not be subtracted from IPHASEA and IPHASEB, respectively. In this case, IPHASEA and IPHASEB are input directly to the traction motor control module  412 , which determines the PWM motor control signal and IAVAILABLE based thereon. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.