Abstract:
A method for operating an electric power generating system (EPGS) includes, in one aspect, detecting current limiting conditions in the SSPC, wherein the SSPC includes a main solid state switch in series with an output filter that includes a first solid state switch, and wherein a decoupling filter comprises a second solid state switch. Another aspect includes, based on the detection of the current limiting conditions in the SSPC, opening the first solid state switch and the second solid state switch; detecting an absence of current limiting conditions in the SSPC; and, based on the detection of the absence of current limiting conditions in the SSPC, closing the first solid state switch and the second solid state switch, and powering a direct current (DC) load by a generator of the EPGS via the output filter and the SSPC.

Description:
FIELD OF INVENTION 
     The subject matter disclosed herein relates generally to the field of electric power generation and distribution systems. 
     DESCRIPTION OF RELATED ART 
     A hybrid vehicle may comprise an electric power generating system (EPGS) integrated with a power distribution system. The power distribution unit may comprise one or more solid state power controllers (SSPCs). Solid State Power Controllers (SSPCs) are used in power distribution systems in, for example, military or aerospace applications, as alternatives to traditional electromechanical circuit breakers. An SSPC may distribute power to and protect various electrical loads. In comparison to electromechanical devices, SSPCs provide relatively fast response time, and may eliminate arcing during turn-off transient and bouncing during turn-on transient. SSPCs also do not suffer severe degradation during repeated fault isolation in comparison with electromechanical devices. SSPCs may be relatively small in weight and size. SSPCs facilitate advanced protection and diagnostics, allowing for efficient power distribution architectures and packaging techniques. However, because the switching device within an SSPC may produce excessive heat during current limiting at elevated current levels due to internal resistances, relatively complex thermal management techniques may be required, that may add complexity, cost and weight to the power distribution system. 
     U.S. patent application Ser. No. 12/720,703, filed on Mar. 10, 2010, and assigned to Hamilton Sundstrand Corp., which is herein incorporated by reference in its entirety, discusses current limiting performed by pulse width modulation (PWM) of a solid-state switch of an SSPC, utilizing the inductance of the feeder between the SSPC output and the DC load. In some applications, such as an aircraft application, the DC bus voltage may be relatively low (about 270 Vdc), and the feeder may have considerable inductance due to a relatively long length. However, in other applications, such as a military ground vehicle, the DC bus voltage may be relatively high (over about 600 Vdc), and the feeder may be relatively short, and have a relatively low inductance. Such high voltage and low feeder inductance conditions may preclude current limiting using PWM of an SSPC switch, even at very high switching frequencies. 
     BRIEF SUMMARY 
     According to one aspect of the invention, an electric power generating system (EPGS) includes a generator configured to power a direct current (DC) load via a power distribution module, the power distribution module comprising a solid state power converter (SSPC); a decoupling filter connected between the generator and the power distribution module, the decoupling filter comprising an inductor connected in parallel with a resistor and a solid state switch, the resistor and solid state switch being connected in series; wherein, during current limiting conditions in the SSPC, the solid state switch of the decoupling filter is configured to be open, and during the absence of current limiting conditions in the SSPC, the solid state switch of the decoupling filter is configured to be closed. 
     According to another aspect of the invention, a method for operating a decoupling filter of an electric power generating system (EPGS), the EPGS comprising a power distribution module comprising a solid state power converter (SSPC), the method including powering a direct current (DC) load by a generator via the SSPC of the power distribution module, wherein the decoupling filter is connected between the generator and the power distribution module, and wherein the decoupling filter comprises an inductor connected in parallel with a resistor and a solid state switch, the resistor and solid state switch being connected in series; during current limiting conditions in the SSPC, opening the solid state switch of the decoupling filter; and during the absence of current limiting conditions in the SSPC, closing the solid state switch of the decoupling filter. 
     Other aspects, features, and techniques of the invention will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Referring now to the drawings wherein like elements are numbered alike in the several FIGURES: 
         FIG. 1  illustrates an embodiment of an electric power generating and distribution system comprising a permanent magnet generator. 
         FIG. 2  illustrates an embodiment of an electric power generating and distribution system comprising an induction generator. 
         FIG. 3  illustrates an embodiment of an electric power generating and distribution system comprising a wound field synchronous generator. 
         FIG. 4  illustrates an embodiment of a decoupling filter. 
         FIG. 5  illustrates an embodiment of an SSPC. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of a decoupling filter for an electric power generating and distribution system comprising an SSPC, and methods of operating a decoupling filter for an electric power generating and distribution system comprising an SSPC, are provided, with exemplary embodiments being discussed below in detail. Use of the decoupling filter allows SSPC technology to be applied to distribution and protection of DC loads, including constant power loads, such as DC-DC converters, export inverters and motor drives, in a high voltage DC power generating and distribution system, which may have relatively low feeder inductance. Current limiting capability at increased DC bus voltage levels may be improved, and inrush current during soft start of capacitive loads may be controlled. Interaction between load channels during overload conditions in any one of the load channels may also be reduced. Voltage regulation at a point of regulation (POR) and power quality on the system bus during current limiting conditions at one or more of the load channels is also improved. Filtering requirements at the front end of the individual loads may also be reduced, and pre-charge function at the individual loads may be eliminated, resulting in lower overall system weight, size, and cost. Lastly, system safety is improved by containing high voltage, high current DC power within the power conversion unit (PCU). 
       FIG. 1  illustrates an electric power generating and distribution system  100  comprising a permanent magnet (PM) generator  102  that generates power from the motion of a prime mover  101 . The PCU  103  connected to the PM generator  102  controls and converts the power from generator  102  to power DC loads  109 A-C. PCU  103  comprises active rectifier  104 , decoupling filter  106 , and a power distribution module  107 . Power distribution module  107  includes a plurality of SSPCs  108 A-C. The SSPCs  108 A-C of power distribution module  107  are each connected to a respective DC load  109 A-C. Each SSPC  108 A-C provides load protective functions for respective DC load  109 A-C, including current limiting during shorted load and inrush current control during capacitive load pre-charge. SSPCs  108 A-C and DC loads  109 A-C are shown for illustrative purposes only; the power distribution module  107  may comprise any appropriate number of SSPCs, each connected to a respective load. The active rectifier  104  controls the system bus voltage at the point of regulation (POR)  105  in response to variable voltage received from the PM generator  102  and variable load conditions. Decoupling filter  106  minimizes voltage distortion at the POR  105  during overload conditions at any of the SSPCs  108 A-C. The decoupling filter  106  comprises a solid-state switch that controls the damping resistance and inductance across decoupling filter  106  based on the operating conditions in power conversion unit  103 , which is discussed below in further detail with respect to  FIG. 4 . SSPCs  108 A-C may also each comprise an optional solid state switch that controls the damping resistance and inductance across the SSPC based on the operating conditions in the SSPC, which is discussed below in further detail with respect to  FIG. 5 . 
       FIG. 2  illustrates an electric power generating and distribution system  200  comprising an induction generator (IM)  202  that generates power from the motion of a prime mover  201 . PCU  203  connected to the IM generator  202  comprises converter  204 , a decoupling filter  206 , and a power distribution module  207 , comprising a plurality of SSPCs  208 A-C. The SSPCs  208 A-C of power distribution module  207  are each connected to a respective DC load  209 A-C. Each SSPC  208 A-C provides load protective functions for respective DC load  209 A-C, including current limiting during shorted load and inrush current control during capacitive load pre-charge. SSPCs  208 A-C and loads  209 A-C are shown for illustrative purposes only; the power distribution module  207  may comprise any appropriate number of SSPCs, each connected to a respective load. Decoupling filter  206  minimizes voltage distortion at the POR  205  during overload conditions at one or more of the SSPCs  208 A-C. The decoupling filter  206  comprises a solid-state switch that controls the damping resistance of decoupling filter  206  based on the operating conditions in power conversion unit  203 , which is discussed below in further detail with respect to  FIG. 4 . SSPCs  208 A-C may also each comprise an optional solid state switch that controls the damping resistance and inductance across the SSPC based on the operating conditions in the SSPC, which is discussed below in further detail with respect to  FIG. 5 . 
       FIG. 3  illustrates an electric power generating and distribution system  300  comprising a wound field synchronous generator (WFSG) generator  302  that generates power from the motion of a prime mover  301 . PCU  303  connected to the WFSG  302  comprises passive rectifier  304 , generator control unit (GCU)  305 , decoupling filter  306 , and power distribution module  307 . Generator control unit  305  controls WFSG  302  based on conditions at the point of regulation located between passive rectifier  304  and decoupling filter  306 . Power distribution module  307  comprises a plurality of SSPCs  308 A-C, which are each connected to a respective DC load  309 A-C. Each SSPC  308 A-C provides load protective functions for respective DC load  309 A-C, including current limiting during shorted load and inrush current control during capacitive load pre-charge. SSPCs  308 A-C and loads  309 A-C are shown for illustrative purposes only; the power distribution module  307  may comprise any appropriate number of SSPCs, each connected to a respective load. Decoupling filter  306  minimizes voltage distortion in the system  300  during overload conditions at one or more of the SSPCs  308 A-C. The decoupling filter  306  comprises a solid-state switch that controls the damping resistance of decoupling filter  306  based on the operating conditions in power conversion unit  303 , which is discussed below in further detail with respect to  FIG. 4 . SSPCs  308 A-C may also each comprise an optional solid state switch that controls the damping resistance and inductance across the SSPC based on the operating conditions in the SSPC, which is discussed below in further detail with respect to  FIG. 5 . 
       FIG. 4  illustrates an embodiment of a decoupling filter  400 , which may comprise any of decoupling filters  106 ,  206 , or  306 . Decoupling filter  400  comprises an inductor  402  connected in parallel with a damping resistor  403  connected in series with a solid state switch  404 . Input  401  may be connected to the POR ( 105 ,  205 ) in the embodiments shown in  FIGS. 1 and 2 , and to the output of the passive rectifier  304  in the embodiment shown in  FIG. 3 . Output  405  is connected to the power distribution module ( 107 ,  207 ,  307 ). During normal operation, the solid state switch  404  is closed to provide system damping across the decoupling filter  400  from damping resistor  403 . When current limiting conditions are present in an SSPC (any of SSPCs  108 A-C,  208 A-C,  308 A-C) located in the power distribution module ( 107 ,  207 ,  307 ) connected to the decoupling filter  400 , the solid state switch  404  is opened to provide additional output impedance from inductor  402  across decoupling filter  400 . The provision of additional output impedance during overload conditions by opening of solid state switch  404  acts to minimize voltage distortion and improve power quality in the EPGS ( 100 ,  200 ,  300 ) during current limiting. 
       FIG. 5  illustrates an embodiment of an SSPC  500 , which may comprise any of SSPCs  108 A-C,  208 A-C, or  308 A-C in a power distribution modules ( 107 ,  207 ,  307 ). Input  501  is connected to the output  405  of the decoupling filter ( 106 ,  206 ,  306 ). During normal operation, power flows across SSPC  500  from input  501  through main solid-state switch  503  to output  513 , which is connected to a DC load ( 109 A-C,  209 A-C,  309 A-C). Main solid state switch  503  is connected across diode  504 . Main solid state switch  503  protects its associated EPGS by disconnecting a faulty load connected to the SSPC  500 , limiting inrush current during pre-charge of capacitive loads via pulse width modulation, and provides current limiting during overload conditions via pulse width modulation in response to the current data received from output current sensor  512 . Overvoltage protection diodes  505  and  511  are connected on the output of switch  503  and filter inductor  508  respectively to a common voltage received from input  502 . The SSPC  500  further comprises an output filter comprising inductor  506 , capacitor  507 , and inductor  508 , connected in parallel with a damping resistor  509  connected in series with a second solid state switch  510 . Second solid state switch  510  is closed to provide additional system damping across the output filter from resistor  509  during current limiting mode of the SSPC  500 , and opened during normal operation of SSPC  500  in order to improve filtering. 
     The technical effects and benefits of exemplary embodiments include improved power quality and minimized voltage distortion in an EPGS during short circuit conditions. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while various embodiment of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.