Abstract:
An improved DC bus regulator that utilizes more transistor packs for power conversion at some times and diode, SCR, and resistor packs at other times. The conversion technology is selected by the regulator based on the current load capacity and response required. For example, transistor packs may be used in low power load conditions. Through use of this hybrid system, the system obtains the desirable effects of transistor pack systems including fast response time, ability to regulate current, and bi-directional power conversion while mitigating the high costs and fragile nature of a system based solely on transistor packs.

Description:
TECHNICAL FIELD 
     This disclosure generally relates to power transmission networks. More specifically, this disclosure relates to operating a DC power system from one or more AC or DC power generators. Even more specifically, this disclosure relates to regulation of energy transfer between an AC and DC power network. 
     BACKGROUND OF THE INVENTION 
     Power transmissions networks can be made of AC systems, DC systems, or a combination of the two. AC power networks have conventionally been used throughout the world. However, DC power networks have certain advantages. DC power networks are easier to design and implement because they introduce no reactance into the power system. Higher efficiencies from generators can be achieved in DC systems because only real power is transmitted. Additionally, parallelization of power supplies is simple because the operating frequency of DC power supplies is 0 Hz. Therefore, no synchronization is required when additional supplies or loads are brought onto the network. 
     The conventional use of AC power networks is a result of the ease of transmitting AC power over long distances and handling voltage changes using transformers. However, over short distances, such as those in isolated environments, a DC power transmission network could be beneficial for the reasons previously explained. High-power generators available today typically produce AC power. Therefore, operation of a DC transmission network powered by AC generators requires conversion from AC to DC and vice versa. 
     Reliable operation of a power network is a critical element of many electronic systems, for example, on drilling platforms or vessels to operate onboard thrusters. Drilling vessels are not anchored in the ocean but are dynamically controlled to maintain a desired position in the ocean. Thrusters are used to maintain a position within specified tolerances of a drilling apparatus. Thrusters are propeller drives which can have variable rotation speed and azimuthal angle of the blades. These thrusters are operated by a power supply onboard the drilling vessel. Any failure of the power supply can lead to displacement of the vessel out of the tolerances of the drilling apparatus. In such a case, the drilling apparatus would need to be mechanically decoupled and recoupled after the power supply is restored and the position of the drilling vessel is corrected. 
     One method of facilitating a reliable power supply is to utilize a DC bus for powering thrusters and other components. Such a power transmission system is demonstrated in  FIG. 1 . In such a system, the power supply is generally made of AC generators coupled to an AC-to-DC converter. The AC-to-DC converter places power from the AC generators on an intermediate DC bus. The intermediate DC bus may be augmented with DC generators or a battery backup system. Each motor or thruster, as well as other devices utilizing the intermediate DC bus, on board the drilling vessel is coupled to the intermediate DC bus through a DC-to-AC converter. 
       FIG. 1  is a block diagram illustrating a conventional DC voltage bus coupling multiple AC voltage generation systems to various loads. Power system  100  includes generators  102 . Generators  102  couple to AC bus  104  through isolators  106 . Isolators  106  allow generators  102  to be removed from the bus when they are not needed or are malfunctioning. AC bus  104  couples to transformer  108  to condition the power for transmission to line  110 . AC-to-DC converter  112  couples to line  110  and converts AC power to DC power for output onto intermediate DC bus  120 . Coupled to DC bus  120  are DC-to-AC converters  130 . DC-to-AC converters  130  convert DC power to AC power which most components are designed to use. Coupled to DC-to-AC converters  130  is line  132  to which loads may be connected. Motor  134  is coupled to line  132 , and motor  134  could be, for example, a thruster. Additionally, transformer  135  is coupled to line  132  to condition power for load  136 . Load  136  could be, for example, a light bulb. 
     There are several methods for implementing the AC-to-DC converter necessary for placing power from the AC generators on the intermediate DC bus. These methods conventionally employ the use of either diodes, silicon-controlled rectifiers (SCRs), or transistors. 
     One apparatus for AC-to-DC power conversion is a diode rectifier (or a diode pack). The are several forms of diode rectifiers commonly known. One typical diode rectifier is a full-wave diode rectifier. The AC power systems on drilling vessels typically utilize a three-phase waveform such that a six diode rectifier configuration is typically used. Diodes conduct current only when the voltage at the anode of the diode is greater than the voltage at the cathode of the diode.  FIG. 2  is a schematic illustrating a conventional diode full-wave rectifier for three-phase AC power. Diode rectifier  200  accepts input from three-phase AC source  202 . The rectifier  200  includes diodes  204  for rectifying the first phase, diodes  206  for rectifying the second phase, and diodes  208  for rectifying the third phase. Two diodes are needed in each case to produce output from both the positive AC cycle and the negative AC cycle. Diodes  204 , diodes  206 , and diodes  208  are coupled between the AC source  202  and the DC bus  210 . Capacitor  212  is coupled to the DC bus  210  to average voltage ripples on DC bus  210 . While rectifier  200  is shown as a single rectifier arrangement, several individual arrangements of one power capacity may be placed in parallel to create a rectifier  200  with a higher power capacity. 
     Diode rectifiers are commercially available from various vendors or can be constructed by arranging individually-purchased diodes. The advantages to diode rectifiers are the low cost of the components. Individual diodes and complete rectifiers are relatively inexpensive for high-power configurations, i.e., several megawatts (MW). Diodes are also relatively small devices compared to other available solutions at an equivalent power load. Diode rectifiers, however, have no ability to regulate the output voltage or current. Additionally, they only conduct in one direction. 
     As a result of the inability to regulate output voltage or current from diode rectifiers, SCRs, also known as thyristor rectifiers, have largely been used in their place.  FIG. 3  is a schematic illustrating a conventional arrangement of SCRs for three-phase AC-to-DC conversion. SCR pack  300  accepts input from three-phase AC source  302 . SCR pack  300  includes SCRs  304  for converting the first phase, SCRs  306  for converting the second phase, and SCRs  308  for converting the third phase. Each individual SCR includes a gate terminal  305  for accepting input. Two SCRs are needed in each case to produce output from both the positive AC cycle and the negative AC cycle. SCRs  304 , SCRs  306 , and SCRs  308  are coupled to AC source  302  and to DC bus  310 . Capacitor  312  is coupled to the DC bus  310  to average ripples on DC bus  310 . While SCR pack  300  is shown as a SCR arrangement, several individual arrangements of one power capacity may be placed in parallel to create a SCR pack  300  with a higher power capacity. 
     Output current may be regulated in the SCRs by controlling through gate terminal  305  when in the AC cycle they turn on. SCRs also offer the low cost, small size, and reliability of diodes. The disadvantage of SCRs is their slow switching time that must occur in synchronization with the AC power supplies. As a result, they are not well suited to handle the power load changes experienced during instability in the power system. Additionally, once the SCR is turned on through gate terminal  305 , it may not be turned off through gate terminal  305 . 
     Transistors offer yet another solution for AC-to-DC power conversion.  FIG. 4  is a schematic illustrating a conventional arrangement of transistors for three-phase AC-to-DC power conversion. Transistor pack  400  accepts input from three-phase AC source  402 . Transistor pack  400  includes transistors  404  to convert the first phase, transistors  406  to convert the second phase, and transistors  408  to convert the third phase. Additionally, diodes  405  are coupled on both sides to transistors  404  to protect transistors  404  from damaging voltages which may develop across transistors  404  and complete the power transfer circuit. This setup is repeated for diodes  407  coupled to transistors  406  and diodes  409  coupled to transistors  408 . Inductors  403  condition the power before reaching transistors  404 , transistors  406 , and transistors  408 . Transistors  404 , transistors  406 , transistors  408  are coupled to AC source  402  and to DC bus  410 . Capacitor  412  is coupled to the DC bus  410  to average ripples on DC bus  410 . While transistor pack  400  is shown as a transistor arrangement, several individual arrangements of one power capacity may be placed in parallel to create a transistor pack  400  with a higher power capacity. 
     Transistors possess faster switching characteristics than SCRs as well as the ability to control on and off timing, making them a better solution under transients resulting from real loads. Additionally, transistors allow power flow in both directions through the converter. This allows power to be moved back from the DC bus to the AC bus. It is typically required that multiple transistor-based conversion devices be placed in parallel to handle large loads. Transistors are expensive devices relative to diodes and SCRs and occupy significantly larger amounts of space. Additionally, transistors are fragile and break easily. 
     Thus, there is a need for a power system that has the fast switching capability of transistors and the low cost, durability, and small footprint of diodes or SCRs. 
     BRIEF SUMMARY OF THE INVENTION 
     An apparatus for interfacing an AC bus and DC bus includes: a set of one or more transistors coupled to the AC bus and coupled to the DC bus; a set of one or more diodes coupled to the AC bus and coupled to the DC bus; and a microcontroller coupled to the set of one or more transistors configured to regulate the current flow through the set of one or more transistors and to regulate the current flow through the set of one or more diodes. The microcontroller can be configured to regulate current through the set of one or more diodes by regulating the voltage on the DC bus. The microcontroller can also be configured to regulate current flow through the set of one or more transistors and the set of one or more diodes such that substantially all power flows through the set of one or more transistors when the power load of the DC bus is within a first power range. The set of one or more transistors can have a first total power capacity and the set of one or more diodes can have a second total power capacity, where the first total power capacity is less than the second total power capacity, and which the first power range can be between zero and a level dynamically chosen, in part, based on the first total power capacity. The apparatus can also include a set of one or more power consuming or storing devices; and a switch coupled to the DC bus and to the set of one or more power consuming devices, in which the microcontroller is further configured to regulate power transfer to the set of one or more power consuming or storing devices. The set of one or more power consuming devices can include resistors. The set of one or more power consuming devices can include capacitors. The set of one or more transistors can includes one or more transistor packs, each transistor pack configured to operate as a separate unit. The apparatus can also include: a switch arranged between the AC bus and one of the transistor packs such that the transistor pack is not directly coupled to the AC bus, the switch coupled to the AC bus, an AC load device, and the transistor pack, in which the switch is configured to alternatively couple the transistor pack to the AC bus or the AC load device; in which the transistor pack is configured to perform AC to DC power conversion when coupled to the AC bus and the DC bus and to perform DC to AC power conversion when coupled to the DC bus and the AC load device. 
     An apparatus for interfacing an AC bus and DC bus includes: a set of one or more transistors coupled to the AC bus and coupled to the DC bus; a set of one or more SCRs coupled to the AC bus and coupled to the DC bus; and a first microcontroller coupled to the set of one or more transistors configured to regulate the current flow through the set of one or more transistors and to regulate the current flow through the set of one or more SCRs. The first microcontroller can be configured to regulate current through the set of one or more SCRs by regulating the voltage on the DC bus. The first microcontroller can further regulate current through the set of one or more SCRs by controlling the gates of the SCRs. The apparatus can also include: a second microcontroller coupled to the one or more SCRs; in which the first microcontroller regulates current through the set of one or more SCRs by signaling the second microcontroller. The microcontroller can be configured to regulate current flow through the set of one or more transistors and the set of one or more SCRs such that substantially all power flows through the set of one or more transistors when the power load of the DC bus is within a first power range. The set of one or more transistors can have a first total power capacity and the set of one or more SCRs can have a second total power capacity, where the first total power capacity is less than the second total power capacity, and which the first power range is between zero and a level that is dynamically chosen, in part, based on the first total power capacity. The apparatus can also include: a set of one or more power consuming devices; and a switch coupled to the DC bus and to the set of one or more power consuming devices, in which the first microcontroller is further configured to regulate power transfer to the set of one or more power consuming devices. The set of one or more power consuming devices can include resistors. The set of one or more power consuming devices can include capacitors. 
     A method for interfacing an AC bus coupled to a set of one or more generators with a DC bus includes: coupling a set of one or more transistors having a first total power capacity to the AC bus and to the DC bus; coupling a set of one or more diodes having a second total power capacity to the AC bus and to the DC bus; and regulating current flow through the set of one or more transistors and the set of one or more diodes such that substantially all power flows through the set of one or more transistors when the power load of the DC bus is within a first power range; wherein the first total power capacity is substantially less than the total power capacity of the set of one or more generators. The first power range can be selected, at least in part, to correspond to the power range in which the overall system, which includes the one or more generators, the AC bus, and the DC bus, is known to be less stable. The first power range can be between zero and a level. The level can be dynamically chosen, in part, based on the first total power capacity. The level can be dynamically chosen, in part, by the capacity of the one or more generators. The regulating current flow step can include regulating voltage on the DC bus. The method also can include: coupling, through a switch, the DC bus to a set of one or more power consuming or storing devices; regulating current flow through the set of one or more power consuming or storing devices when the power load of the DC bus is above a second level. The second level can be dynamically chosen, in part, based on the first total power capacity. 
     An apparatus for AC to DC and DC to AC power conversion includes: a set of one or more transistor packs, each transistor pack configured to operate as a separate unit coupled to an AC bus and a DC bus; a switch arranged between the AC bus and one of the transistor packs such that the transistor pack is not directly coupled to the AC bus, the switch coupled to the AC bus, an AC load device, and the transistor pack, in which the switch is configured to alternatively couple the transistor pack to the AC bus or the AC load device; in which the transistor pack is configured to perform AC to DC power conversion when coupled to the AC bus and the DC bus and to perform DC to AC power conversion when coupled to the DC bus and the AC load device. The apparatus can also include: a second switch arranged between the AC bus and a second one of the transistor packs such that the second transistor pack is not directly coupled to the AC bus, the switch coupled to the AC bus, an AC load device, and the second transistor pack, in which the switch is configured to alternatively couple the second transistor pack to the AC bus or the AC load device; in which the second transistor pack is configured to perform AC to DC power conversion when coupled to the AC bus and the DC bus and to perform DC to AC power conversion when coupled to the DC bus and the AC load device. 
     An apparatus for interfacing an AC bus and DC bus includes: a set of one or more transistors coupled to the AC bus and coupled to the DC bus; a set of one or more SCRs coupled to the AC bus and coupled to the DC bus; and a microcontroller coupled to the set of one or more transistors configured to regulate the current flow through the set of one or more transistors and to regulate the current flow through the set of one or more SCRs. The microcontroller can be configured to regulate current through the set of one or more SCRs by regulating the voltage on the DC bus. The microcontroller can be configured to regulate current flow through the set of one or more transistors and the set of one or more SCRs such that substantially all power flows through the set of one or more transistors when the power load of the DC bus is within a first power range. The set of one or more transistors can have a first total power capacity and the set of one or more SCRs can have a second total power capacity, where the first total power capacity is less than the second total power capacity, and which the first power range is between zero and a level that is dynamically chosen, in part, based on the first total power capacity. The apparatus can also include: a set of one or more power consuming or storing devices; and a switch coupled to the DC bus and to the set of one or more power consuming devices, in which the microcontroller is further configured to regulate power transfer to the set of one or more power consuming or storing devices. The set of one or more power consuming devices can include resistors. The set of one or more power consuming devices can include capacitors. The set of one or more transistors can include one or more transistor packs, each transistor pack configured to operate as a separate unit. The apparatus can also include: a switch arranged between the AC bus and one of the transistor packs such that the transistor pack is not directly coupled to the AC bus, the switch coupled to the AC bus, an AC load device, and the transistor pack, in which the switch is configured to alternatively couple the transistor pack to the AC bus or the AC load device; in which the transistor pack is configured to perform AC to DC power conversion when coupled to the AC bus and the DC bus and to perform DC to AC power conversion when coupled to the DC bus and the AC load device. 
     An apparatus for interfacing an AC bus and DC bus includes: a set of one or more transistors coupled to the AC bus and coupled to the DC bus; a set of one or more SCRs coupled to the AC bus and coupled to the DC bus; and a first microcontroller coupled to the set of one or more transistors configured to regulate the current flow through the set of one or more transistors and to regulate the current flow through the set of one or more SCRs. The first microcontroller can be configured to regulate current through the set of one or more SCRs by regulating the voltage on the DC bus. The first microcontroller can further regulates current through the set of one or more SCRs by controlling the gates of the SCRs. The apparatus can also include: a second microcontroller coupled to the one or more SCRs; in which the first microcontroller regulates current through the set of one or more SCRs by signaling the second microcontroller. The microcontroller can be configured to regulate current flow through the set of one or more transistors and the set of one or more SCRs such that substantially all power flows through the set of one or more transistors when the power load of the DC bus is within a first power range. The set of one or more transistors can have a first total power capacity and the set of one or more SCRs can have a second total power capacity, where the first total power capacity is less than the second total power capacity, and which the first power range is between zero and a level that is dynamically chosen, in part, based on the first total power capacity. The apparatus can also include: a set of one or more power consuming devices; and a switch coupled to the DC bus and to the set of one or more power consuming devices, in which the first microcontroller is further configured to regulate power transfer to the set of one or more power consuming devices. The set of one or more power consuming devices can include resistors. The set of one or more power consuming devices can include capacitors. 
     A method for interfacing an AC bus coupled to a set of one or more generators with a DC bus includes: coupling a set of one or more transistors having a first total power capacity to the AC bus and to the DC bus; coupling a set of one or more SCRs having a second total power capacity to the AC bus and to the DC bus; and regulating current flow through the set of one or more transistors and the set of one or more SCRs such that substantially all power flows through the set of one or more transistors when the power load of the DC bus is within a first power range; wherein the first total power capacity is substantially less than the total power capacity of the set of one or more generators. The first power range can be selected, at least in part, to correspond to the power range in which the overall system, which includes the one or more generators, the AC bus, and the DC bus, is known to be less stable. The first power range can be between zero and a level. The level can be dynamically chosen, in part, based on the first total power capacity. The level can be dynamically chosen, in part, based on the capacity of the one or more generators. The regulating current flow step can include regulating voltage on the DC bus. The method can also include: coupling, through a switch, the DC bus to a set of one or more power consuming or storing devices; regulating current flow through the set of one or more power consuming or storing devices when the power load of the DC bus is above a second level. The second level can be dynamically chosen, in part, based on the first total power capacity. 
     An apparatus for AC to DC and DC to AC power conversion includes: a set of one or more transistor packs, each transistor pack configured to operate as a separate unit coupled to an AC bus and a DC bus a switch arranged between the AC bus and one of the transistor packs such that the transistor pack is not directly coupled to the AC bus, the switch coupled to the AC bus, an AC load device, and the transistor pack, in which the switch is configured to alternatively couple the transistor pack to the AC bus or the AC load device; in which the transistor pack is configured to perform AC to DC power conversion when coupled to the AC bus and the DC bus and to perform DC to AC power conversion when coupled to the DC bus and the AC load device. The apparatus can also include: a second switch arranged between the AC bus and a second one of the transistor packs such that the second transistor pack is not directly coupled to the AC bus, the switch coupled to the AC bus, an AC load device, and the second transistor pack, in which the switch is configured to alternatively couple the second transistor pack to the AC bus or the AC load device; in which the second transistor pack is configured to perform AC to DC power conversion when coupled to the AC bus and the DC bus and to perform DC to AC power conversion when coupled to the DC bus and the AC load device. 
     An apparatus for use in with an AC generator, an AC load, and a DC bus, includes: a transistor pack configured to perform AC-to-DC power conversion and DC-to-AC power conversion, the transistor pack including at least a first input and a second input; a first switch coupled to the AC generator, the AC load, the DC bus, and the first input of the transistor pack, the first switch arranged to connect the first input of the transistor pack to the AC generator, the AC load, or the DC bus; a second switch coupled to the AC generator, the AC load, the DC bus, and the second input of the transistor pack, the second switch arranged to connect the second input of the transistor pack to the AC generator, the AC load, or the DC bus; and a microcontroller configured to, in a first instance, instruct the first switch and the second switch to connect the first and second inputs of the transistor pack so that the transistor pack may convert AC power from the AC generator to DC power for the DC bus and to, in a second instance, instruct the first switch and the second switch to connect the first and second inputs of the transistor pack so that the transistor pack may convert DC power from the DC bus to AC power for the AC load. The microcontroller may be configured to instruct the first switch to connect the first input of the transistor pack to the AC generator and instruct the second switch to connect the second input of the transistor pack to the DC bus so that the transistor pack may convert AC power from the AC generator to DC power for the DC bus, and may be further configured to instruct the first switch to connect the first input of the transistor pack to the DC bus and instruct the second switch to connect the second input of the transistor pack to the AC load so that the transistor pack may convert DC power from the DC bus to AC power for the AC load. 
     A method for using a transistor pack capable of performing AC-to-DC, DC-to-AC, or DC-to-DC conversion in conjunction with a generator, a load, and a DC bus, includes: coupling the transistor pack to the generator and the DC bus such that the transistor pack may perform AC-to-DC or DC-to-DC conversion. The method also includes coupling the transistor pack to the DC bus and the load such that the transistor pack may perform DC-to-AC conversion or DC-to-DC conversion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
         FIG. 1  is a block diagram illustrating a conventional DC voltage bus coupling multiple AC voltage generation systems to various loads. 
         FIG. 2  is a schematic illustrating a conventional six diode full-wave diode rectifier. 
         FIG. 3  is a schematic illustrating a conventional arrangement of SCRs for AC-to-DC conversion. 
         FIG. 4  is a schematic illustrating a conventional arrangement of transistors. 
         FIG. 5  is a graph illustrating the different operating regions experienced by a power conversion system according to one embodiment of the invention. 
         FIG. 6  is a schematic illustrating an exemplary DC bus regulator using a transistor pack and a diode pack according to one embodiment of the invention. 
         FIG. 7  is a schematic illustrating an exemplary DC bus regulator using a transistor pack and a SCR pack according to one embodiment of the invention. 
         FIG. 8  is a schematic illustrating an exemplary DC bus regulator using a resistor according to one embodiment of the invention. 
         FIG. 9  is a schematic illustrating an exemplary DC bus regulator using a resistor and capacitor according to one embodiment of the invention. 
         FIG. 10  is a block diagram illustrating a swing pack for AC-to-DC, DC-to-AC, and DC-to-DC conversion according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Fast switching characteristics in a DC bus regulator are more likely to be needed at some times than others. Under certain conditions it is more likely that the load scenario can be unpredictable and experience rapid changes making fast switching necessary to maintain the stability of the power system. For example, in the case of a power system on an offshore drilling rig, the power system tends to be unstable where the loads are small compared to the online generator capacity. Under these unstable conditions, the quick reaction time of transistors is desirable. However, when the power system is stable, fast switching may not be required. Where the fast switching of transistors is not needed, diodes or SCRs may be a more durable and cost-effective solution for power conversion. 
     By recognizing that the fast switching ability of transistors are only needed during certain system conditions, such as low power load as compared to generator capacity scenarios for an offshore drilling rig power system, a system may be designed to include transistors capable of only handling a fraction of the total power load along with diode or SCRs to handle the remaining load. Thus, such a hybrid system may be reduced in size and cost as compared to an all transistor system for the same total power load while still maintaining fast switching ability when needed. Realization of such a system is not possible by simply combining the two technologies since both technologies perform generally the same function. Rather, creation of a hybrid system requires utilizing a control system that recognizes power conditions during which fast switching is more likely to be needed and power conditions during which the system is likely to be more stable. 
       FIG. 5  is a graph illustrating the different operating regions experienced by an exemplary DC bus regulator in an offshore drilling rig power system according to one embodiment of the invention. Chart  500  plots power flow through the DC bus regulator on y-axis  501  versus power consumption by the DC bus on x-axis  502 . Lines  503 ,  504 ,  505 , and  506  represent the total capacity of the transistors included in the exemplary DC bus regulator, which is only a fraction of the total capacity of the system, as illustrated by lines  507  and  508 . Region  51  covers forward conduction from the AC generators to the DC bus. Region  51  has two operational modes. In region  511 , the transistors are in forward conduction. In region  512 , the transistor capacity has been exceeded and diodes are switched on to assist in handling the larger load. Region  52  covers reverse conduction from the DC bus to the AC generators. Region  52  has two operational modes. In region  521 , the transistors function in reverse conduction. In region  522 , the capacity of the transistors has been exceeded and a set of resistors or other power consumption or storage devices are switched on to consume additional power off the DC bus.  FIG. 5  illustrates one exemplary operating graph. Lines  503 ,  504 ,  505 , and  506  may be pre-defined levels or dynamically chosen based on the operating conditions of the power system. Other alternatives are discussed below and those skilled in the art will recognize others based on the teachings herein. 
       FIG. 6  is a schematic illustrating an exemplary DC bus regulator utilizes transistor packs and diode packs according to one embodiment of the invention. Regulator  600  may be used to implement the operational graph shown in  FIG. 5 . Regulator  600  accepts input from three-phase AC source  602  conditioned by transformer  604 . A typical value for AC source  602  in one application may be 11 kV. Transformer  604  outputs voltage onto line  610  and line  620 . A typical value for lines  610  and  620  is 600 V, but they need not be equal. Transistor pack  612  may be coupled to line  610  and DC bus  614 . Transistor pack  612  may be implemented, at least partially, using transistor pack  400  in  FIG. 4 . Diode pack  622  may be coupled to line  610  and DC bus  614 . Diode pack  622  may be implemented, at least partially, using diode rectifier  200  in  FIG. 2 . Microcontroller  613  is operatively connected to transistor pack  612  to control the current flow through and output voltage of transistor pack  612 . Microcontroller  613  may be any control system capable of controlling transistor pack  612  such as, for example, a programmable microprocessor, a digital signal processor (“DSP”), field programmable gate array (“FPGA”), application specific integrated circuit (“ASIC”), or any other logical device. Microcontroller  613  may be integrated with transistor pack  612  or may be separate. In another embodiment, transistor pack  612  may independently monitor the voltage of DC bus  614  and regulate current flow through transistor pack  612 . In yet another embodiment, loads connected to regulator  600  may be configured to provide input to microcontroller  613  about future power demands. 
     Turning to  FIG. 5 , in region of operation  511 , a substantial portion of the total energy passing through regulator  600  will pass through transistor pack  612 . In a preferred embodiment, this is accomplished by microcontroller  613  controlling transistor pack  612  such that the voltage on DC bus  614  is at a level below the voltage on line  620 , causing the diodes to not conduct. Microcontroller  613  may control the system such that all current flows through transistor pack  612  or simply such that a substantial portion flows through transistor pack  612  and a smaller portion flows through diode pack  622 . When the power load increases such that region of operation  512  is entered, additional energy will flow through diode pack  622 . This may be accomplished in a preferred embodiment by microcontroller  613  configuring transistor pack  612  to modify the voltage on DC bus  614  to enable conduction through diode pack  622 . When operation re-enters region  511 , microcontroller  613  configures transistor pack  612  to modify the voltage on DC bus  614  to disable or substantially reduce conduction through diode pack  622 . When operating in region  512 , power conduction through transistor pack  612  may, in some embodiments, be significantly reduced or terminated. As discussed in detail below, this may allow transistor pack  612  or some portion thereof to be used in other operations around the distribution network. It should be noted that the border between regions  511  and  512  need not be the absolute capacity of the available transistors. Rather, the border may be an appropriate value taking into account the available resources of regulator  600  and the operating characteristics of the system. 
     Another embodiment of a system that converts AC-to-DC power combines transistor packs and SCR packs. Advantages of this design are the fast response time of the transistors and the high capacity, low cost, and controllable current of the SCRs. SCRs operate in the simplest case identical to diodes but have the added feature of current control through gate timing. 
       FIG. 7  is a schematic illustrating an exemplary DC bus regulator using a transistor pack and an SCR pack according to one embodiment of the invention. Regulator  700  may, for example, implement the system illustrated in  FIG. 5 . Transistor pack  612  is coupled to line  610  to DC bus  614 , similar to regulator  600 . SCR pack  722  may be coupled to line  620 , after conditioning by inductors  723 , and to DC bus  614 , similar to the placement of diode pack  622  in  FIG. 6 . SCR pack  722  may be implemented, at least partially, using SCR pack  300  in  FIG. 3 . In region of operation  511 , a substantial portion of the total energy passing through regulator  700  will pass through transistor pack  612 . In a preferred embodiment, microcontroller  613  may control power flow through transistor pack  612  in order to regulate the voltage on DC bus  614 . In one embodiment, microcontroller  613  also couples to SCR pack  722 . Microcontroller  613  may control the gates of the SCRs in SCR pack  722  to enable power flow through SCR pack  722 . Alternatively, the microcontroller  613  may control a second microcontroller (not illustrated) that controls the SCRs. 
     Another embodiment of a system that converts AC to DC power combines transistors with diodes or SCRs and resistors. Diodes and SCRs as shown in  FIG. 6  and  FIG. 7  may be used to augment the capacity of transistors when the forward power exceeds the transistor&#39;s capacity. However, diodes and SCRs only conduct in one direction preventing them from allowing reverse power flow. In operating region  522 , resistors, batteries, capacitors, or other storage devices may be added to remove power from DC bus. 
       FIG. 8  is a schematic illustrating an exemplary DC bus regulator using resistors according to one embodiment of the invention. Regulator  800  accepts input from AC source  602  after conditioning by transformer  604  into line  610  and line  620 . Transistor pack  612  couples line  610  to DC bus  614  and diode pack  822  couples line  620  to DC bus  614 . An SCR pack could be used in place of diode pack  822  to achieve similar results, as illustrated in  FIG. 7 . Additionally, transistor pack  832  couples resistors  834  to DC bus  614 . Transistor pack  832  may be comprised of transistors which may be similar to the transistors used in transistor pack  612 , or may be any other switching component with the necessary operational characteristics. Transistor pack  832  may be controlled by microcontroller  613  to enable or disable resistors  834 . In reverse power operation region  521  as illustrated in  FIG. 5 , power may flow through transistor pack  612  back to AC source  602 . When the power capacity of transistor pack  612  is reached, microcontroller  613  may enable transistor pack  832  allowing power to flow to resistors  834  and dissipate as heat. When operation returns to region  521 , microcontroller  613  may turn off transistor pack  832  and power flow occurs only through transistor pack  612 . As discussed above, the border between regions  521  and  522  need not be the absolute capacity of the available transistors. Rather, the border may be an appropriate value taking into account the available resources of regulator  800  and the operating characteristics of the system. 
     Although resistors provide power consumption when power needs to be taken off the DC bus, the power is lost in heat dissipation. Since generators consume resources to generate the energy taken off the DC bus, it would be preferable to store the energy in such a means that the energy may be put back on the DC bus at a later time. Such a configuration would increase efficiency and reduce the cost of operating the generators for the power system. Additionally, stored energy may respond more dynamically to changes in power loads. Sudden increases in power demand are difficult to accommodate with AC generators due to the length of response time required to increase fuel consumption to generate the needed power. Furthermore, autonomy from the generators is obtained, because a sudden failure of the AC generators may be compensated by the stored power. 
       FIG. 9  is a schematic illustrating an exemplary DC bus regulator using a resistor and capacitor for reverse power regulation according to one embodiment of the invention. Regulator  900  accepts input from AC source  602  after conditioning by transformer  604  into line  610  and line  620 . Transistor pack  612  couples line  610  to DC bus  614  and diode pack  822  couples line  620  to DC bus  614 . An SCR pack could be used in place of diode pack  822  to achieve similar results. Additionally, switch  942  couples capacitors  944  and resistors  946  to DC bus  614 . Switch  942  may be controlled by microcontroller  613  to enable or disable capacitors  944 . Additionally, switch  950  and switch  952  coupled to capacitors  944  and resistors  946 , respectively, allow energy to be stored in capacitors  944  or dissipated through resistors  946 . In reverse power operation region  521  power may flow through transistor pack  612  back to AC source  602 . When the power capacity of transistor pack  612  is reached, microcontroller  613  may enable  942  allowing power to flow to capacitors  944 . When operation returns to region  521 , microcontroller  613  may turn off switch  942  and power flow occurs only through transistor pack  612 . Regulator  900  may also use a combination of resistors and capacitors in place of capacitors  944 . Further, any other energy dissipation or energy storage technology may be used in combination or as a substitution for capacitors  944  such as rotating masses or batteries. 
     Although the present disclosure has described in detail using three-phase AC sources, one skilled in the art may readily modify the disclosure in this application to operate on a two phase or other AC system, or from DC generators. 
     In the design of  FIG. 1  multiple AC-to-DC converters are required as are multiple DC-to-AC converters and DC-to-DC converters. For example, motor  134  may operate on AC power and therefore it is necessary to convert the power on the DC bus back to AC before it may be utilized by motor  134 . One skilled in the art will recognize that DC-to-AC power conversion may be accomplished using similar components as are used for AC-to-DC power conversion. For example, transistor pack  612  as shown in  FIG. 6 ,  FIG. 7 ,  FIG. 8 , and  FIG. 9  may be configured to perform DC-to-AC conversion. Also, DC-to-DC power conversion may be accomplished using similar components as DC-to-AC and AC-to-DC power conversion. 
     In the different regions of operation exemplarily shown in  FIG. 5 , as power flow is diverted from transistors to diodes or SCRs, at least a portion of the transistor pack no longer in use may be switched from converting AC-to-DC power for the DC bus to convert DC-to-AC power for an attached load, energy storage device, or resistor. Such a configuration may reduce the number of transistors required for the power system illustrated in  FIG. 1  thereby reducing the space requirements and the cost of the overall power system. 
       FIG. 10  is a block diagram illustrating a swing pack for AC-to-DC, DC-to-AC, and DC-to-DC conversion according to one embodiment of the invention. Power system  1000  includes bank of converters  1002 . Bank of converters  1002  may be any number or combination of devices capable of AC-to-DC, DC-to-AC, and DC-to-DC conversion, such as transistor pack  400  illustrated in  FIG. 4 . Bank of converters  1002  are coupled on one side to DC bus  1020  and on another side to isolators  1004 . Isolators  1004  when closed couple one converter of bank  1002  to line  1014  leading to AC or DC generators or to line  1012  leading to AC or DC loads. The isolators may be controlled, for example, by a microcontroller or other control system that may be separate or the same as microcontroller  613 . Inductor  1006  conditions power before reaching line  1012  or line  1014 . The selection of which power consumption units are engaged in generator to DC bus power transfer or DC bus to load may be based on the process at hand. For example, use of on power pack of bank  1002  to pass power to an energy storage device would be done when the DC bus had excess power and therefore the power pack would not need to be engaged in moving power from the generator to the DC bus. 
     Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the present invention, disclosure, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.