Patent Publication Number: US-2012046794-A1

Title: Intelligent DC Power Management System

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to U.S. provisional patent application Ser. No. 61/372,489, filed on Aug. 11, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     Present day power needs for vehicular, airborne, and ground-based electrical systems are growing. Traditional electro-mechanical sensors, relays, lamps, propulsion systems, and operating-status equipment are being replaced by more efficient, compact, yet higher power density converters and power distribution controllers. Consequently, typical direct current (“DC”) power levels demanded by today&#39;s power loads are approaching nearly 500 A, which creates problems with the use of large copper-conductors, and especially with thermal magnetic circuit breakers typically used for overload protection. Thermal magnetic circuit breakers have both electrical and physical limitations that restrict their usage in today&#39;s high efficiency and high reliability applications. One limitation of particular concern is their inherent higher in-circuit impedance resulting in higher power dissipation which impacts the overall efficiency. In addition, since thermal magnetic circuit breakers are a mechanical device they are large and heavy. Furthermore, they are difficult to actuate from an electronic control and/or monitoring system. Lastly, circuit breakers will mechanically wear out, and therefore require either preventive maintenance or replacement to insure reliable operation. 
     Typical DC power management systems utilize large enclosures constructed to house large busbar connections, large DC magnetic circuit breakers, large electro-magnetic contactors for DC power load control, current shunt resistors, and large wire connections. The use of circuit breakers and electro-mechanical relays are commonly found in devices utilized for DC power management. However, these devices are physically large and dissipate large amounts of power during normal operation. 
     Measuring DC current is typically accomplished by a current sensing device placed in the current path of the power circuitry. The current sensing device may be a passive device or an active device. A passive current sensing device senses current by measuring the potential difference across a resistor to obtain a proportional measure of current though the resistor by way of Ohm&#39;s law. An active current sensing device senses current by measuring the magnetic field about a current carrying conductor to obtain a proportional measure of current by way of the Hall Effect. These current sensing devices dissipate heat during normal operation. Also, there are a number of mechanical connections needed to connect these sensing devices with other parts of the circuit, and these connections introduce resistance, which could generate a sizable amount of heat. 
     Existing power management systems have power handling densities of about 12 watts/in 3 . Some systems require forced air, or liquid cooling to reliably distribute the necessary power to DC loads. The use of such cooling options requires additional power itself, and has other physical limitations. 
     SUMMARY OF THE INVENTION 
     The invention may be implemented as a control system for distribution of direct current electricity to one or more load systems. Such a distribution system may include one or more electronic power switches (“EPSs”), each having an input terminal and an output terminal. Each EPS may be a MOSFET. Each EPS input terminal may be electrically connected to the same supply of direct current electricity. 
     One or more loads may be connected to the output terminals of the EPSs. As such, each EPS may control the supply of direct current electricity to a different load, or more than one EPS may be used to supply direct current electricity to the same load. 
     One or more current sensors may be included in the distribution system to monitor the current being supplied by each EPS. The current sensors may be active current sensors or passive current sensors. For example, a Hall-effect current sensor may be used. 
     The distribution system may have a micro-controller that is programmed to control operation of the EPSs. The micro-controller can be used to provide DC electric power via the EPSs to a single load system or multiple load systems, either via a single EPS or multiple EPSs. The program executed by the micro-controller may have instructions for causing the micro-controller to determine a level of DC current supplied to one or more load systems, and for causing the micro-controller to adjust the one or more EPSs in response to the determined DC current level(s). 
     For example, the program may cause the micro-controller to adjust the one or more EPSs during turn-on and/or turn-off of the load systems that draw power from the one or more EPSs. The EPSs may be controlled by the micro-controller to limit the current supplied to the load systems. 
     Adjustments made by the micro-controller may be accomplished according to user-defined parameters that are stored in a computer-readable medium that has the program stored or embedded thereon. The program may include instructions for causing the EPSs to turn on in small increments. For example, the increments may be selected to limit individual or aggregate load currents to levels which are within maximum operating parameters of the EPSs. The program may include instructions for causing the EPSs to control the EPSs so that the power supplied by each EPS to the loads at a safe level. The micro-controller can be used to sequentially power individual load systems such that high-power distribution currents typically experienced during turn-on of such load systems are reduced, or eliminated. 
     The DC current distribution control system may be implemented using a printed circuit board and circuit layout which lowers parasitic inductance and increases current throughput. 
     The invention may be implemented as a method of controlling the distribution of DC electric power. In one such method, one or more EPSs are provided. Each EPS has an input terminal and an output terminal. The input terminals may be electrically connected to one another. One or more current sensors are provided and arranged to monitor DC electric current supplied by at least one of the EPSs. A programmed microcontroller, which is in communication with the EPSs, is used to control distribution of DC electric current by adjusting the current supplied by the output of each EPS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       For a fuller understanding of the nature and objects of the invention, reference should be made to the accompanying drawings and the subsequent description. Briefly, the drawings are: 
         FIG. 1  is a block diagram of a DC power management system that is in keeping with the invention; 
         FIG. 2  depicts an interface; 
         FIG. 3  is a flow diagram for an algorithm that may be used in the invention; and 
         FIG. 4  is a flow chart of a method that is in keeping with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An intelligent DC power management system is disclosed herein. Since the embodiments shown in the drawings are for illustrative purposes, some sub-components and/or peripheral components generally incorporated in the disclosure are omitted from this description for purposes of brevity and clarity. In describing embodiments in accordance with the present invention, specific terminologies are employed for sake of clarity. However, the invention is not intended to be limited to the selected terminologies and specified embodiments described herein. It should be stressed that the invention may be embodied in many different forms, and the figures should not be construed as limiting to the particular embodiments depicted in the figures. Rather, the figures are provided to illustrate how the invention might be implemented. 
     The present invention relates to systems and methods for distributing and controlling DC electric power. One such a system  50  may be used to provide high efficiency (i.e. low power loss) in a battery-operated system. In particular, the invention may be used with systems commonly found on airborne or ground-based vehicles. Also, the invention may be particularly well suited for use with DC power sources such as solar-electricity generators, as well as thermal and chemical conversion devices which produce DC current, or as a voltage converter. 
     The invention may use a micro-controller (CPU  104 ) to analyze current use by the loads  400 , and to control one or more EPSs  107 ,  109 . EPSs  107 ,  109  are particularly well suited since their power-loss is low, they have the ability to handle a large range of power, and they are highly efficient. The EPSs  107 ,  109  may be MOSFETs which have been arranged electrically in parallel with one another. Such an arrangement affords better current-sharing among these devices in a reliable and compact manner. For example, the CPU  104  may be programmed to adjust one or more of the EPSs  107 ,  109  during turn-on and/or turn-off of loads  400  that draw power from the one or more EPSs  107 ,  109 . Doing so may entail controlling one or more of the EPSs  107 ,  109  to limit the current supplied to load systems  400  associated with those EPSs  107 ,  109 . The invention also may be implemented to facilitate the use of user-defined parameters that may be provided to the CPU  104  remotely via a user network interface  304 . 
     The program executed by the CPU  104  may be provided via a memory device that is readable by the CPU  104 . The memory device may include instructions executable by the CPU  104  to provide a default set of operating instructions, and/or the memory device may be programmable so that special operating characteristics may be realized. For example, the program may include instructions for causing the CPU  104  to control the EPSs  107 ,  109  in order to keep the power supplied by each EPS  107 ,  109  at a safe level. To illustrate, in order to start supplying electricity to one of the loads  400 , the CPU  104  may be programmed to cause one of the EPS  107 ,  109  to turn on in small increments so that other loads  400  do not experience a sudden drop in electricity. Also, the increments may be selected to limit individual or aggregate load current to levels that do not exceed maximum operating parameters of the EPSs  107 ,  109 . 
       FIG. 1  is a general block diagram and schematic representation of an intelligent DC power management system  50  according to one embodiment of the present invention. The system line voltage (+)  10  may be connected to a space/weight efficient connector system (not shown), whose objective is to provide low resistance connections in order to reduce loss of power being delivered to the load, which can be internally connected via low-loss conductor  200  to one or more low loss, solid-state current sensors  106 ,  108 . As used herein, the term “low loss” means a low resistance material or device that is either the primary current conductor or measurement device inserted in the primary conductor path. Being “low loss” the material or device provides a higher level of efficiency, which translates into improved performance of the system that employs such a material or device. The current sensors  106 ,  108  may be active or passive current sensors, or a combination of these. As an example, the current sensor may be an Allegro Micro-Systems Model ACS758. 
     The current sensors  106 ,  108  may interpret and transmit information about the current being handled to one or more EPSs  107 ,  109 . For example, the current information may be the amperage being supplied to the load systems  400 . In  FIG. 1 , current sensor  106  communicates information to the EPS  107 . Similarly in  FIG. 1 , the current sensor  108  communicates information to the EPS  109 . 
     External power source  1  may be connected to the DC power management system  50  by an interface  301 .  FIG. 2  depicts an interface  301  that may be used in the invention. The interface  301  depicted in  FIG. 2  is a ruggedized circular connector (A) which incorporates a socket contact(s) (B) for attachment of a conductor. A highly conductive (e.g. OFHC, CA101) adaptor (C) may be designed to fit into the socket contact (B) where it is metallurgically bonded to (B). This adaptor provides a highly conductive land area for attachment to a bus-bar (D) using a cone-shaped washer (E) and machined screw fastener (F) for near constant force loading of conductive surfaces. This combination, together with an appropriate amount of anti-oxidant compound, provides a low resistance connection that is superior to that which can be provided by a conventional wire connection to the socket contact(s). 
     Input power conditioning device  100  may provide protective and mitigating capability in order to guard against unwanted disturbances from the power source  1  reaching components of the distribution system  50 . A first power supply  101  may provide a regulated voltage for powering the operation of the current sensors  106 ,  108  and EPSs  107 ,  109 . A second power supply  102  may provide a voltage that is isolated from the system line  10  voltage for providing power necessary to operate a main central processing unit (“CPU”)  104 . In this manner, differing power requirements of the EPSs  107 ,  109  and the CPU  104  may be accommodated. 
     The main CPU  104  may communicate with each EPS  107 ,  109  via an EPS  107 ,  109  communication interface  110  in order to implement operational parameters desired by a user, and provide operational commands for each EPS  107 ,  109  to control operation of the EPS  107 ,  109 . The CPU  104  preferably has built-in core functions like adequate Flash memory, RAM, Serial I/O, GP I/O, and multi-channel 12-bit A/D converters. In addition, each EPS  107 ,  109  may utilize the communication interface  110  to communicate information to the main CPU  104  about the operational status of the EPS  107 ,  109  (e.g. “on”, “off”, or “fault”), and the output conditions (e.g. current and voltage) associated with each EPS  107 ,  109 . A galvanic isolation device  105  can provide electrical isolation between the main CPU  104  and EPSs  107 ,  109  so that current is prevented from reaching ground, for example, by a person&#39;s body. 
     The main CPU  104  may receive system operation commands via a user network interface  304 . For example, the user network interface may be one which meets the standards of Ethernet IEEE 802, CAN (Controller Area Network) SAE J1939, or other standard, as required by the user. The user network interface  304  may be used to report operational status of the power management system  50 , or its components, as directed by the user. Galvanic isolation device  103  may provide electrical isolation between the user network and the main CPU in order to protect the main CPU from the vagaries of the network. 
     Commands, including program instructions, may be provided to the main CPU  104  via the switch input  111 , and in this manner inputs may be provided to the CPU  104  without using the network interface  304 . Local status indications may be provided from the CPU  104  via indicator outputs  112 . In this manner, a person may interact with the CPU  104  when located at the distribution system  50 . 
     Via the switch input  111 , a user may provide operating parameters and/or program code, and the system&#39;s  50  response may be provided to the user via switch output  112 . In this manner, proper equipment safety, set-up, and maintenance may be accomplished locally without the need to interface via the network interface  304 . 
     Each EPS  107 ,  109  may manage the application of power to equipment (“load systems”), which are connected to one of the output connections  302 ,  303 . EPSs  107 ,  109  may be MOSFETs which have been arranged electrically in parallel with one another. The EPS  107 ,  109  adjusts the power delivered to a load by controlling the MOSFET during on and off command transitions, as well as going to an off command upon detection of a fault. When arranged in parallel, the EPSs  107 ,  109  may share current in a more reliable and compact manner than existing circuit breakers and relays. The EPSs  107 ,  109  can manage power application using an algorithm which takes into account the operational parameters provided to the main CPU  104 . The algorithm may be selected to keep the output on/off profiles of the load systems  400 , which are powered via the EPSs  107 ,  109 , within prescribed operating limits. In addition, the algorithm may be used to monitor the power dissipated in the MOSFET array and provide control commands in order to maintain the MOSFET array within a predetermined safe operating parameters. 
     The algorithm may be accomplished by means of hardware and software in a manner that protects the load as well as the EPSs  107 ,  109  and the MOSFET array. For example, hardware may be used to provide fast response to a high surge overload condition, and software may be used to provide control in other situations to keep system parameters within acceptable limits and provide appropriate timing for carrying out commands, as well as dynamic configuration. For example, software may be used to control the EPS  107 ,  109  to maintain the current delivered to the load  400  within a safe operating limit.  FIG. 3  is a flow diagram depicting such an algorithm. That algorithm measures  405  the system line voltage  10 , the output voltage (voltage supplied to the load  400 ), the current being supplied to that load  400 , and a temperature that is important to the system. For example, the temperature of a case that covers and protects the system  50  may be monitored. The SOA is computed  408 , which is a parameter found by multiplying the measured current with the difference between the system line voltage  10  and the output voltage. An output command is retrieved  411 , which is an indication as to whether the load should be turned on or off. If the command is to turn off, then the system provides  417  a command to turn off power being supplied to the load  400 . However, if the command is to turn on, then one or more comparisons are made  414 . For example, the calculated SOA may be compared to an SOA threshold, the measured current may be compared to a current threshold, the output voltage may be compared to a voltage threshold, and the measured temperature may be compared to a threshold temperature. If any of these parameters are determined to be unacceptable with respect to the threshold, a determination is made that the system is out of limits and a command is sent  417  to the relevant EPS  107 ,  109  instructing it to turn off. If all parameters are determined to be acceptable with respect to the threshold, then a determination is made that the system is within limits and a command is sent  420  to the relevant EPS  107 ,  109  instructing it to turn on. Then, the status of the system is updated  423 , and the algorithm may then begin again to sample voltages and current. 
     The outputs  302 ,  303  of each EPS  107 ,  109  may be monitored by the current sensing devices  106 ,  108 , and if the output exceeds desired limits, the EPSs  107 ,  109  may be instructed to take appropriate action to mitigate the excessive condition. For example, current supplied to a load system  400  may be reduced or turned off, and the action taken may be communicated to the main CPU  104 . The main CPU  104  may then report the condition and actions to a user via the user network interface  304  for consideration by an overall system program that may be operating on a remote computer that is under the user&#39;s control. 
     A system  50  according to the invention may utilize air to maintain proper operating temperatures. The EPSs  107 ,  109  may be configured to achieve a low resistance, thereby minimizing unnecessary power dissipation while simultaneously improving operating efficiency. For example, the EPSs  107 ,  109  may be arranged to accomplish low resistance by paralleling MOSFET devices. When activated, MOSFET&#39;s exhibit an expected “on resistance”, but the resultant resistance is much lower when a number of MOSFET&#39;s are placed in parallel. In this manner it is possible to achieve a resistance of less than 500 micro-Ohm&#39;s, which yields reduced heat loss and improved efficiency. 
     Additionally, the configuration for the EPSs  107 ,  109  may be selected to afford an efficient means of moving heat away from the EPSs  107 ,  109  to a location outside the enclosure  999 . In doing so, ambient air and natural convection currents may be used to move unwanted heat away from the EPSs  107 ,  109 . In one such method of moving unwanted heat, the EPSs  107 ,  109  are mounted within an enclosure or chassis. For example, the EPSs  107 ,  109  may be mounted against the floor of the chassis by using thermal gap material to provide electrical isolation while achieving good thermal conductivity. Also, the EPSs  107 ,  109  may be positioned to have a short heat conduction path with regard to heat generated by the MOSFET array. Even though the generated heat from power MOSFET&#39;s are small, that heat must have an efficient path in order to move the heat away from the devices. For example, this may be accomplished by mounting the EPS  107 ,  109  against the wall of the enclosure that will provide the most cross-sectional surface area for heat conduction. To electrically isolate the MOSFET from the chassis, while providing a thermally conductive path, a thermal pad may be used which has excellent electrical isolation properties while high thermal conductive properties. 
     It will now be recognized that  FIG. 1  depicts a system  50  for controlling DC power distribution in which EPS  107 ,  109  are used as the primary current control and distribution device. Each EPS  107 ,  109  has an input terminal and an output terminal, and when more than one EPS  107 ,  109  is provided, the input terminals may be electrically connected to one another so that the EPSs  107 ,  109  share a supply of power. 
     The amount of current supplied by each EPS  107 ,  109  to a load system  400  may be monitored with one or more current sensors  106 ,  108 . In addition, the power provided by each EPS  107 ,  109  may be monitored. It should be noted that outlets of the EPSs  107 ,  109  may be connected to the same loads  400 , or different loads  400 . In this manner, the CPU  104  can be used to sequentially power individual load systems  400  such that high-power distribution currents typically experienced during turn-on of some load systems  400  are reduced, or eliminated. 
     By using the invention described herein, it is possible to create a system having 0.15-0.20 watts per square inch of surface area, thereby achieving an average external case temperature rise of 30 degrees Celsius at 100,000 feet or 20 degrees Celsius at sea level. At an average of 0.15 watts per square inch of surface area, it may be possible to achieve an average external case temperature rise of about 25 degrees Celsius. In addition, it is possible to achieve electrical efficiency of about 98.5%, or higher. 
     It is possible to construct a device that uses the techniques described herein that will operate within a temperature range of −40 to +71 degrees Celsius with typical operating voltage selections of +12, +24, +28, and −48Vdc. 
     Finally, it should be recognized that the invention allows for connecting directly to a primary power bus, without the need for intermediate input voltage conditioning. Also, the device and its protection mechanisms may be self-contained and need not require additional support apparatus. For example, such an apparatus might require additional connectivity to provide electromagnetic filtering, transient voltage suppression, voltage pre-regulators, or active clamping devices. Further, when the invention is implemented as a self-contained device, the input and output connections are directly connected to the switching devices using low loss materials and connection techniques. In addition, appropriately tight package placement using layered PCB stack-up can be used to accomplish pseudo bus-bar conductor behavior within the PCB to minimize inductance and resistance. 
     The invention may be embodied as a method of controlling the distribution of DC electric power.  FIG. 4  shows steps of such a method. In one such method, one or more EPSs are provided  500 . Each EPS has an input terminal and an output terminal. The input terminals may be connected to each other so that the voltage at each input terminal is approximately the same. A load system may be connected to one or more of the output terminals. Current sensors may be provided  503  to monitor DC electric current supplied by each EPS, and the current supplied to the loads may be monitored  506 . Information from this monitoring effort may be provided  509 . Using the provided information, DC electric current from each output terminal is controlled  512  using the EPSs, thereby affording control and distribution of the DC electric power to the connected load systems. 
     Although embodiments of the invention have been described herein, the invention is not limited to such embodiments. The claims which follow are directed to the invention, and are intended to further describe the invention, but are not intended to limit the scope of the invention.