Abstract:
Systems and methods for providing power to a refrigeration unit or an air conditioner used on a hybrid vehicle. The system includes an accumulation choke, a PWM rectifier, and a frequency inverter. The accumulation choke is configured to receive a first AC power, a second AC power, and a DC power. The accumulation choke and PWM rectifier convert the received power into an intermediate DC power having a peak voltage. The PWM rectifier provides the intermediate DC power to the frequency inverter. The frequency inverter converts the intermediate DC power to an output AC power. The frequency inverter provides the output AC power to the refrigeration unit.

Description:
RELATED APPLICATION 
     The present application claims the benefit of prior filed U.S. Provisional Patent Application No. 61/158,964 filed on Mar. 10, 2009, the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     Refrigeration units, e.g., for refrigerated trucks or rail cars, typically include an internal combustion engine which drives a compressor of the refrigeration unit via a belt. Some refrigeration units also include means for plugging the unit into electrical mains (shore power) for powering the unit when the unit is not in transit. The shore power powers an electric motor which drives the compressor via a belt. 
     SUMMARY 
     In one embodiment, the invention provides a power system for powering a refrigeration unit. The power system includes a first set of connections, a second set of connections, and a third set of connections. The first set of connections are configured to receive power from a first power source, the first power source being a first high-voltage AC power source. The second set of connections are configured to receive power from a second power source, the second power source being a high-voltage DC power source. The third set of connections are configured to receive power from a third power source, the third power source being a second high-voltage AC power source. The power system couples the first power source to the refrigeration unit when power is received at the first set of connections, couples the second power source to the refrigeration unit when power is received at the second set of connections but not the first set of connections, and couples the third power source to the refrigeration unit when power is not available from both the first and second set of connections. 
     In another embodiment, the invention provides a power system for powering a refrigeration unit. The power system includes a first connection, a second connection, a third connection, and a power converter. The first connection is configured to receive power from a first power source. Where the first power source is a first high-voltage alternating current (AC) power source. The second connection is configured to receive power from a second power source. Where the second power source is a high-voltage direct current (DC) power source. The third connection is configured to receive power from a third power source. Where the third power source is a second high-voltage AC power source. The power converter is configured to supply power to the refrigeration unit. The power system couples the first power source to the power converter when power is received at the first connection, couples the second power source to the power converter when power is received at the second connection but not the first connection, and couples the third power source to the power converter when power is not available from both the first and second connections. 
     In another embodiment, the invention provides a system for powering a refrigeration unit coupled with a hybrid vehicle having a plurality of high-voltage batteries. The system includes a power system, a refrigeration control unit, and an engine. The power system is coupled to the plurality of high-voltage batteries and is configured to receive power from a shore power source. The refrigeration control unit is coupled to the power system, and receives an indication from the power system of the availability of power from the high-voltage batteries and the shore power source. The engine is also coupled to the refrigeration control unit. The refrigeration control unit links power from the power system to the refrigeration unit when power is available from the power system, and links the engine to the refrigeration unit when power is not available from the power system. 
     In another embodiment, the invention provides a method of powering a refrigeration unit. The method includes the acts of receiving at a first input a high-voltage DC power from a plurality of batteries of a hybrid vehicle, receiving at a second input a high-voltage AC power from an electric mains, connecting one of the first input and the second input to a power converter based on a position of a switch, the connecting act coupling one of the high-voltage DC power and the high-voltage AC power to the power converter thereby resulting in a coupled power, disconnecting the coupled power from the power converter when the position of the switch has changed, converting the coupled power into a second high-voltage AC power, and providing the second high-voltage AC power to the refrigeration unit. 
     The invention relates to systems and methods for powering a refrigeration or air conditioning unit used with a hybrid vehicle, such as a truck or bus. In one embodiment, the invention uses high-voltage power from the batteries of the hybrid vehicle to power the refrigeration unit, while maintaining the capability of using shore power or operating the compressor using an internal combustion engine when the power available from the batteries is not available. 
     In another embodiment, the invention provides a system for providing power to a refrigeration unit used on a hybrid vehicle. The system includes an accumulation choke, a PWM rectifier, and a frequency inverter. The accumulation choke is configured to receive a first AC power having a voltage range of about 150 to 600 VAC, a second AC power of about 150 to 600 VAC, and a DC power having a voltage range of about 263 to 408 VDC. The accumulation choke and PWM rectifier convert the received power into an intermediate DC power having a peak voltage of about 750 VDC. The PWM rectifier provides the intermediate DC power to the frequency inverter. The frequency inverter converts the intermediate DC power to a variable output AC power having a voltage of about 0 to 525 VAC and a frequency of about 0 to 100 Hertz (Hz). The frequency inverter provides the output AC power to the refrigeration unit. 
     In another embodiment, the invention provides a system for providing power to a refrigeration unit used on a hybrid vehicle. The system includes an accumulation choke, a PWM rectifier, and a frequency inverter. The accumulation choke is configured to receive an AC power having a voltage range of about 150 to 600 VAC and a DC power having a voltage range of about 263 to 408 VDC. The accumulation choke and PWM rectifier convert the received power into an intermediate DC power having a peak voltage of about 750 VDC. The PWM rectifier provides the intermediate DC power to the frequency inverter. The frequency inverter converts the intermediate DC power to an output AC power having a voltage of about 0 to 525 VAC. The frequency inverter provides the output AC power to the refrigeration unit. If the AC power and the DC power are not available, the refrigeration unit is driven by an internal combustion engine. 
     In yet another embodiment, the invention provides a method of providing power to a refrigeration unit used on a hybrid vehicle. The method includes providing to a power unit a first AC power from an external source, providing to the power unit a DC power from high-voltage batteries of the hybrid vehicle, determining if the first AC power is sufficient to power the refrigeration unit, using the first AC power to generate an output AC power if the first AC power is determined to be sufficient to power the refrigeration unit, determining if the DC power is sufficient to power the refrigeration unit, using the DC power to generate the output AC power if the first AC power is not sufficient to power the refrigeration unit and the DC power is sufficient to power the refrigeration unit, generating the output AC power from a belt driven alternator if the first AC power and the DC power are not sufficient to power the refrigeration unit, and providing the output AC power to the refrigeration unit. 
     In another embodiment, the invention provides a system for powering a refrigeration unit of a hybrid vehicle. The system includes an external source of power, a power unit for receiving AC power from the external source of power, a battery charger receiving AC power from the external source of power, and a plurality of batteries forming a high-voltage battery for powering the hybrid vehicle. The power unit modifies the AC power into an output AC power suitable to operate the refrigeration unit. The charger recharges the plurality of batteries. 
     Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram of a construction of a power system for a hybrid vehicle with a refrigeration unit. 
         FIG. 1B  is a block diagram of an alternative construction of a power system for a hybrid vehicle with a refrigeration unit. 
         FIG. 2A  is a schematic diagram of a construction of an accumulation choke and a full-control PWM rectifier for use with three-phase AC power. 
         FIG. 2B  is a schematic diagram of a construction of an accumulation choke and a half-control PWM rectifier for use with three-phase AC power. 
         FIG. 3A  is a schematic diagram of a construction of an accumulation choke and a full-control PWM rectifier for use with DC power. 
         FIG. 3B  is a schematic diagram of a construction of an accumulation choke and a half-control PWM rectifier for use with DC power. 
         FIG. 4  is a block diagram of a construction of a system for powering a refrigeration unit of a hybrid vehicle. 
         FIG. 5  is a schematic diagram of a construction of a circuit of a power system for using AC or DC power to generate three-phase AC power. 
         FIG. 6  is a schematic diagram of a construction of a circuit for controlling the operation of the circuit of  FIG. 5 . 
         FIG. 7  is an alternative construction of a power system for powering multiple systems. 
         FIGS. 8A and 8B  are a schematic diagram of another construction of a power system. 
         FIGS. 9A, 9B, 9C, and 9D  are a schematic diagram of another construction of a power system. 
         FIG. 10  is a block diagram of another construction of a system for powering a refrigeration unit of a hybrid vehicle. 
         FIG. 11  is a schematic diagram of another construction of a circuit of a power system for using AC or DC power to generate three-phase AC power. 
         FIG. 12  is a schematic diagram of a construction of a full-control PWM rectifier, incorporating a pre-charge circuit, for use with three-phase AC power. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
       FIG. 1A  shows a block diagram of a construction of a system  100  for powering a refrigeration unit  105  using power from a belt driven alternator  110 , from high-voltage batteries  115  of a hybrid vehicle, and from shore power  120 . A switch  125  selects which of the three power sources  110 ,  115 , and  120  is used. In some constructions, the switch  125  is a manual switch, where a user selects which power source  110 ,  115 , and  120  to use. In other constructions, the switch  125  is automatic, where a controller senses which power source(s) are providing sufficient power to operate the refrigeration unit  105  and selects the most appropriate power source to use. For example, in some embodiments, shore power  120  is used whenever it is available, followed by power from the high-voltage batteries  115 , and finally by power from the belt driven alternator  110 . In addition, the controller may control operation of an internal combustion engine used to drive the alternator, turning on the engine when there is insufficient power available from the shore power  120  or the high-voltage batteries  115 , and turning off the engine when there is sufficient power available from either the shore power  120  or the high-voltage batteries  115 , thus saving energy (i.e., fuel). 
     In some constructions, the power available from the belt driven alternator  110  is about 150 to 600 volts AC (VAC), the power available from the high-voltage batteries  115  is about 263 to 408 volts DC (VDC), and the power available from shore power  120  is about 150 to 600 VAC. In the construction shown, AC power is assumed to be three-phase, however the invention contemplates the use of single-phase AC power as well. 
     Depending on the position of the switch  125 , set either manually or automatically, the power from one of the power sources  110 ,  115 , and  120  is applied a power converter  130  including an accumulation choke  135 , a pulse-width-modulated (PWM) rectifier  140 , and a frequency inverter  145 . The accumulation choke  135  is coupled to the PWM rectifier  140 . The accumulation choke  135  operates with the PWM rectifier  140  to convert/modify the power received from the belt driven alternator  110 , the high-voltage batteries  115 , or the share power  120  to a DC voltage having a maximum amplitude of about 750 VDC. The DC voltage is provided to the frequency inverter  145  which converts the DC voltage to a variable voltage of 0 to 525 VAC having a frequency of about 0 to 100 Hz, which is provided to the refrigeration unit  105 . In some constructions, the DC power from the PWM rectifier  140  is also used to supply a DC chopper for an electric heater. The DC chopper provides DC power having a variable voltage of about 0 to 750 V DC. 
       FIG. 1B  shows a block diagram of an alternate construction of a system  100 ′ for powering a refrigeration unit  105  using power from a belt driven alternator  110 , from high-voltage batteries  115  of a hybrid vehicle, and from shore power  120 . Again a switch  125 ′ selects which of the three power sources  110 ,  115 , and  120  is used. However, in the construction shown, the switch  125 ′ has multiple throws such that when power from the belt driven alternator  110  is selected, the alternator  110  is connected directly to the PWM rectifier  140 , bypassing the accumulation choke  135 . Except for the alternator  110  being connected directly to the PWM rectifier  140 , the operation of the system  100 ′ is the same as the operation of system  100  described above. The construction shown in  FIG. 1B  can be used when the inductance of the belt driven alternator  110  is great enough that the accumulation choke  135  is not necessary. 
       FIG. 2A  shows a schematic diagram of a construction of the accumulation choke  135  and a full-controlled PWM rectifier  140 ′. The accumulation choke  135  includes a plurality of inductors  150 . The full-controlled PWM rectifier  140 ′ includes six insulated gate bipolar transistors (IGBT)  155 - 160 , each IGBT  155 - 160  having a diode  165 - 170  connected across its collector and emitter, and a capacitor  175 . 
       FIG. 2B  shows a schematic diagram of a construction of the accumulation choke  135  and a half-controlled PWM rectifier  140 ″. The accumulation choke  135  includes a plurality of inductors  150 . The half-controlled PWM rectifier  140 ″ includes three insulated gate bipolar transistors (IGBT)  158 - 160 , each IGBT  158 - 160  having a diode  168 - 170  connected across its collector and emitter, three diodes  155 - 157  connected in an upper branch of the half-controller PWM rectifier  140 ″, and a capacitor  175 . 
       FIG. 3A  shows a schematic representation of the accumulation choke  135  and a full-controlled PWM rectifier  140 ′ for use with DC input power from the high-voltage batteries  115 . The accumulation choke  135  and the full-controlled PWM rectifier  140 ′ include all the same components as described above with respect to  FIG. 2A ; however, the DC input voltage is applied to each inductor  150  and the upper IGBTs  155 - 157  are not used (i.e., they remain open). 
       FIG. 3B  shows a schematic diagram of a construction of the accumulation choke  135  and a half-controlled PWM rectifier  140 ″ for use with DC input power from the high-voltage batteries  115 . The accumulation choke  135  includes a plurality of inductors  150 . The half-controlled PWM rectifier  140 ″ includes three insulated gate bipolar transistors (IGBT)  158 - 160 , each IGBT  158 - 160  having a diode  168 - 170  connected across its collector and emitter, three diodes  155 - 157  connected in an upper branch of the half-controller PWM rectifier  140 ″, and a capacitor  175 . 
       FIG. 4  shows a block diagram of a construction of a hybrid vehicle system  200  including a refrigeration unit  205 . The system  200  includes, among other things, a 12 VDC battery  210 , a set of high-voltage batteries  215 , a vehicle controller  220 , a refrigeration unit controller  225 , a refrigeration power system  230  including a connection to shore power  240 , a refrigeration unit power switch  245 , and a generator set including an internal combustion engine  250  driving an alternator  255 . In some constructions, an internal combustion engine  250  drives a compressor and fans of the refrigeration unit  205  directly by one or more belts. In some constructions, an electric motor is powered by the shore power  240  and drives a compressor and fans of the refrigeration unit  205  directly by one or more belts. 
     A master switch  260  enables the entire system  200 . The power system  230  receives power from the shore power connection  240  and the high-voltage batteries  215 , and provides power, if available, from either the shore power connection  240  or the high-voltage batteries  215  to the refrigeration unit power switch  245 . 
     The vehicle controller  220  provides an indication to the power system  230 , via line  265 , that power is available from the high-voltage batteries  215 . The power system  230  provides to the refrigeration unit controller  225 , via line  270 , an indication that power is available from either the shore power connection  240  or the high-voltage batteries  215 , and is being provided to the refrigeration unit power switch  245 . The refrigeration unit controller  225  provides to the power unit  230 , via line  275 , an indication that the refrigeration unit  205  is on or off. The refrigeration unit controller  225  controls the refrigeration unit power switch  245 , switching between power provided by the power system  230  or, if power is not available from the power system  230 , power provided by the belt driven alternator  255 . If the refrigeration unit  205  is on, power is provided to the refrigeration unit  205  by the power system  230  if power is available from either the shore power connection  240  or the high-voltage batteries  215 . If power is not available from the power system  230  and the refrigeration unit  205  is on, the refrigeration unit controller  225  turns on the internal combustion engine  250  which drives, via a belt, the alternator  255 . The alternator  255  then provides power to the refrigeration unit power switch  245 , which is set, by the refrigeration unit controller  225 , to provide the power from the alternator  255  to the refrigeration unit  205 . In alternative constructions, there may be no alternator present in the system  200 , instead the internal combustion engine  250  drives a compressor and fans of the refrigeration unit  205  directly. 
       FIG. 5  shows a construction of a portion of the power system  230 . The system  230  includes an AC power connector  300  and a DC power connector  305 . The AC connector  300  includes three connections L 1 , L 2 , and L 3  for connecting three-phase shore power (if available) to the system  230 . The DC connector  305  includes a positive  310  and a negative  315  connection for connecting to the high-voltage batteries  115 . Each input line L 1 , L 2 , L 3 ,  310 , and  315  is connected to the rest of the system  230  through a fuse FSUP 1 -FSUP 5  sized appropriately for the voltage and current received on its respective input line L 1 , L 2 , L 3 ,  310 , and  315 . Each input line L 1 , L 2 , L 3 ,  310 , and  315  is also connected to the power converter  130  through a normally-open relay  320 - 326 . As discussed below, when shore power is available, the normally-open relays  320 - 322  are closed to provide the AC shore power to the power converter  130 , and when shore power is not available and DC power from the high-voltage batteries  115  is available, the normally-open relays  323 - 326  are closed to provide the DC power to the power converter  130 . When the AC normally-open relays  320 - 322  are closed, the DC normally-open relays  323 - 326  are open, and when the DC normally-open relays  323 - 326  are closed, the AC normally-open relays  320 - 322  are open. In some constructions, an interlock module monitors relays  320 - 322  and  323 - 326  to ensure that only one of the relay groups  320 - 322  or  323 - 326  is closed at any time. 
     The system  230  also includes AC pre-charging circuits having normally-open relays  330  and  331  and resistors  332  and  333 , and a DC pre-charging circuit including a normally-open relay  334  and resistor  335 . The pre-charging circuits are used when power is initially applied to the power system  230 , and during a transition from AC power to DC power or from DC power to AC power. During a transition, the pre-charging circuits maintain power to the power converter  130 , and allow the AC or DC power to be completely removed before the DC or AC power, being transitioned to, is connected. 
     As discussed above with respect to  FIGS. 1-3 , if available, AC or DC power is provided to the accumulation choke  135  and the PWM rectifier  140  of the power converter  130 . The accumulation choke  135  and the PWM rectifier  140  convert the AC or DC power to DC power having a maximum voltage of about 750 volts. The DC power is the provided to the inverter  145  which converts the DC power to three-phase AC power having a variable voltage of 0 to 525 volts and frequency of about 0 to 100 Hz. In the construction shown in  FIG. 4 , this AC power is then provided to the refrigeration unit  205  via the refrigeration unit power switch  245 . In some constructions, the DC power from the PWM rectifier  140  is also used to supply a DC chopper for an electric heater. The DC chopper provides DC power having a variable voltage of about 0 to 750 V DC. 
       FIG. 6  shows a circuit  350  for controlling the application of AC or DC power to the power converter  130  for the system  230  shown in  FIG. 5 . The circuit  350  includes an AC delay  355  having a normally-closed switch  360  and a normally-open switch  365 , a DC delay  370  having a normally-closed switch  375  and a normally-open switch  380 , and a plurality of coils  390 - 396  for closing corresponding normally-open relays  320 - 326  shown in  FIG. 5 . A switch  400  selects either AC or DC power. In the construction shown, the switch  400  is a manual switch requiring an operator to select the AC or DC power. In some embodiments, the switch  400  is an automatic switch where AC power is automatically chosen if available, and if AC power is not available but DC power is available, DC power is automatically chosen. In other embodiments, DC power is automatically chosen if available and AC power is chosen if available when DC power is not available. In some embodiments, if the switch  400  is off, and neither AC nor DC power is available, an internal combustion engine drives the refrigeration unit directly when the refrigeration unit is on. 
     When the switch  400  is put into the AC position, power is provided to the AC delay  355  and to the AC pre-charge coil  395 . The power provided to the AC pre-charge coil  395  closes the AC pre-charge normally-open relays  330 - 331  ( FIG. 5 ) applying AC power through resistors  332  and  333  to the power converter  130 . After a delay period (e.g., five seconds), the AC delay  355  opens the AC normally-closed switch  360  and closes the AC normally-open switch  365 . When the AC normally-closed switch  360  opens, power is removed from the AC pre-charge coil  395  and the AC pre-charge normally-open relays  330 - 331  open. When the AC normally-open switch  365  closes, power is applied to the AC coil  396  and the AC normally-open relays  320 - 322  close providing three-phase AC power to the power converter  130 . 
     When the switch  400  is put into the DC position, power is provided to the DC delay  370  and to the DC pre-charge coil  391 , and to DC negative coil  390 . The power provided to the DC pre-charge coil  391  closes the DC pre-charge normally-open relay  334  ( FIG. 5 ) applying DC power through resistor  335  to the power converter  130 . The power provided to the DC negative coil  390  closes the normally-open relay  326  connecting the negative connection  315  from the high-voltage batteries  215  to the power converter  130 . After a delay period (e.g., five seconds), the DC delay  370  opens the DC normally-closed switch  375  and closes the DC normally-open switch  380 . When the DC normally-closed switch  375  opens, power is removed from the DC pre-charge coil  391  and the DC pre-charge normally-open relay  324  opens. When the DC normally-open switch  380  closes, power is applied to the DC coils  392 - 394  and the DC normally-open relays  323 - 325  close providing DC power to the power converter  130 . 
       FIG. 7  shows an alternative construction of a power converter  405  where multiple power converters  410 - 425  are employed for powering various devices such as a compressor motor  430 , an electric heater  435 , an evaporator fan  440 , and a condenser fan  445 . 
       FIGS. 8A and 8B  show a schematic diagram of a construction of the power system  230  ( FIG. 4 ). When system power is turned on (switch  260  in  FIG. 4  is closed), normally-open relay K 7  closes. If shore power is available, i.e., three-phase AC power is provided to L 1 , L 2 , L 3 , and a phase select module  450  receives power from normally-open relay K 7  and the AC power lines L 1 , L 2 , L 3 . The phase select module  450  then provides power to line  8 EA. The power on line  8 EA initiates a five second delay timer  455  and simultaneously powers coil P. The power to coil P closes normally-open relays P 1  and P 2 , and opens normally-closed relay P 2 . After five seconds, the five second delay timer  455  provides power to output MPT which is provided to the refrigeration unit controller  225  to indicate that power is available from the power system  230  ( FIG. 4 ). If the refrigeration unit controller  225  indicates that the refrigeration unit  205  is on, normally-open relay K 13  is closed providing power to coil MCA. The power to coil MCA causes normally-open relays MCA to close, supplying the AC shore power to the power converter  130 , which in turn supplies power to a condenser motor  460  (providing normally-open relays K 14  are closed). 
     If AC shore power is not available, normally-closed relay P 2  is closed. If the vehicle controller  220  ( FIG. 4 ) indicates that vehicle power is available, the vehicle controller  220  provides power to a five second delay timer  465 . After a five second delay, the timer  465  allows power to be applied to a coil T closing normally-open relay T 1  and providing power to output MPT, which is provided to the refrigeration unit controller  225  to indicate that power is available from the power system  230  ( FIG. 4 ). If the refrigeration unit controller  225  indicates that the refrigeration unit  205  is on, normally-open relay K 13  is closed, providing power to coil MCB. The power to coil MCB causes normally-open relays MCB to close, supplying the DC power from the high-voltage batteries  215  to the power converter  130 , which in turn supplies power to the condenser motor  460  (providing normally-open relays K 14  are closed). 
     If neither AC shore power nor DC power from the high-voltage batteries  215  is available, the output MPT to the refrigeration unit controller  225  is low and the refrigeration unit controller  225  starts the engine  250  which drives the refrigeration unit  205  directly. 
       FIGS. 9A, 9B, 9C, and 9D  show a schematic diagram of an alternative construction of a power system  500 . 
       FIG. 10  shows an alternate construction of a power system  505 . The system  505  includes a first AC power connector  510 , a second AC power connector  515 , and a DC power connector  520 . The first AC connector  510  includes three connections L 1 , L 2 , and L 3  for connecting three-phase power from the belt driven alternator  255  to the system  505 . The second AC connector  515  includes three connections L 1 ′, L 2 ′, and L 3 ′ for connecting three-phase shore power (if available) to the system  505 . The DC connector  520  includes a positive connection  525  and a negative  530  connection for connecting to the high-voltage batteries  215  to the system  505 . Each input line L 1 , L 2 , L 3 , L 1 ′, L 2 ′, L 3 ′,  525 , and  530  is connected to the rest of the system  505  through a fuse FSUP 1 -FSUP 8  sized appropriately for the voltage and current received on its respective input line L 1 , L 2 , L 3 , L 1 ′, L 2 ′, L 3 ′,  525 , and  530 . Each input line L 1 , L 2 , L 3 , L 1 ′, L 2 ′, L 3 ′,  525 , and  530  is also connected to the power converter  130  through a normally-open relay  535 - 544 . As discussed below, when shore power is available, the normally-open relays  538 - 540  are closed to provide the AC shore power to the power converter  130 , and when shore power is not available and DC power from the high-voltage batteries  215  is available, the normally-open relays  541 - 544  are closed to provide the DC power to the power converter  130 . When neither shore power nor DC power is available, the normally-open relays  535 - 537  are closed to provide AC power from the alternator  255  to the power converter  130 . Only one set of normally-open relays  535 - 537 ,  538 - 540 , or  541 - 544  are closed at any time. 
     The system  505  also includes first AC pre-charging circuits having normally-open relays  550  and  551  and resistors  552  and  553 , second AC pre-charging circuits having normally-open relays  555  and  556  and resistors  557  and  558 , and a DC pre-charging circuit having a normally-open relay  560  and a resistor  561 . The pre-charging circuits are used when power is initially applied to the power system  505 , and during a transition between one input power to another to maintain power to the power converter  130  during the transition, and allowing the power being transitioned from to be completely removed before the power being transitioned to is connected. 
     As discussed above with respect to  FIGS. 1-3 , if available, AC or DC power is provided to the accumulation choke  135  and the PWM rectifier  140  of the power converter  130  convert the AC or DC power to DC power having a maximum voltage of about 750 volts. The DC power is the provided to the inverter  145 , which converts the DC power to three-phase AC power having a voltage of 0 to 525 volts. In the construction shown in  FIG. 4 , this AC power is then provided to the refrigeration unit  205  via the refrigeration unit power switch  245 . 
       FIG. 11  shows a circuit  600  for controlling the application of the first AC power, the second AC power, or the DC power to the power converter  130  for the system  505  shown in  FIG. 10 . The circuit  600  includes a first AC delay  605  having a normally-closed switch  610  and a normally-open switch  615 , a second AC delay  620  having a normally-closed switch  625  and a normally-open switch  630 , a DC delay  635  having a normally-closed switch  640  and a normally-open switch  645 , and a plurality of coils  650 - 658  for closing corresponding normally-open relays  534 - 544 ,  550 - 551 ,  555 ,  556 , and  560  shown in  FIG. 10 . A switch  660  selects either the first AC power, the second AC power, or the DC power. In the construction shown, the switch  660  is a manual switch requiring an operator to select the power. In some constructions, the switch  660  is an automatic switch where the second AC power (shore power) is automatically chosen if available, and if the first AC power is not available but DC power is available, the DC power is automatically chosen. If neither the second AC power nor the DC power is available, the switch automatically chooses the first AC power. The circuit  600  operates similar to the operation of circuit  350  of  FIG. 6  with the addition of a second AC power. 
     In some constructions, a liquid cooling system of the hybrid vehicle is used to cool one or more components of the power system  230  (e.g., the power converter  130 ) and/or one or more components of the alternator  255  (e.g., the belt driven alternator  110 ). In other constructions, a liquid cooling system of the refrigeration unit  205  is used to cool one or more components of the power system  230  and/or one or more components of the alternator  255 . 
     In some constructions, shore power is provided to a charging circuit, in addition to the power system  230 , for charging the high-voltage batteries  215 . In some constructions, the refrigeration unit  205  is operated exclusively using either DC power from the high-voltage batteries  215  or AC shore power  240 . 
       FIG. 12  shows a schematic diagram of an alternative construction of a full-controlled PWM rectifier  700  incorporating a pre-charging circuit  705 . The full-controlled PWM rectifier  700  includes six insulated gate bipolar transistors (IGBT)  155 - 160 , each IGBT  155 - 160  having a diode  165 - 170  connected across its collector and emitter, and operates the same as system  100  described above. The pre-charging circuit  705  includes a capacitor  715 , a resistor  720 , a diode  725 , and an IGBT  730 . The pre-charging circuit  705  operates to buffer a current surge encountered when switching from one power source to a second power source, and eliminates the need for the pre-charging and delay circuits described for the controllers above. The pre-charging circuit  705  operates by opening the IGBT  730  prior to transitioning the power source. Applying the second power source and removing the first power source while the IGBT  730  is open. The IGBT  730  is held open until the capacitor  715  is fully charged forcing current to travel through the resistor  720 . Once the capacitor  715  is fully charged, the IGBT  730  is closed. 
     Constructions of the invention are capable of being used in non-hybrid vehicles, receiving AC power from an alternator of the vehicle during operation of the vehicle and having a shore power connection for use when the vehicle is not operating. 
     Thus, the invention provides, among other things, systems and method for powering a refrigeration unit of a hybrid vehicle.