Various embodiments may provide non-isolated single-input dual-output (SIDO) bi-directional buck-boost direct current (DC) to DC (DC-DC) converters. Various embodiments may provide a method for controlling a buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter such that a first voltage measured across a first portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than a voltage of a first load and a second voltage measured across a second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than a voltage of a second load.

TECHNICAL FIELD

The present invention is generally directed to power generation systems and in particular to direct current (DC) to DC (DC-DC) converters for power generation systems.

BACKGROUND

Electrochemical devices, such as fuel cells, can convert energy stored in fuels to electrical energy with high efficiencies. In a fuel cell system, such as a solid oxide fuel cell (SOFC) system, an oxidizing flow is passed through the cathode side of the fuel cell while a fuel inlet flow is passed through the anode side of the fuel cell. The oxidizing flow is typically air, while the fuel flow can be a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. The fuel cell enables the transport of negatively charged oxygen ions from the cathode flow stream to the anode flow stream, where the ion combines with either free hydrogen or hydrogen in a hydrocarbon molecule to form water vapor and/or carbon monoxide to form carbon dioxide. The excess electrons from the negatively charged ion are routed back to the cathode side of the fuel cell through an electrical circuit completed between anode and cathode, resulting in an electrical current flow through the circuit.

SOFC systems may be used to power many different devices under many different arrangements. As an example, SOFC systems may be used to charge batteries and/or to power micro-grids. In SOFC system applications, direct current (DC) to DC (DC-DC) converters are popular to support high efficiency operations of the SOFC systems. Specifically, bi-directional DC-DC converters are widely used in battery charging and micro-grid applications.

Therefore, there is a need for techniques which can overcome one or more limitations stated above, in addition to providing other technical advantages.

SUMMARY

This summary is provided only for the purposes of introducing the concepts presented in a simplified form. This is not intended to identify essential features of the claimed invention or limit the scope of the invention in any manner.

Various embodiments may provide a non-isolated single-input dual-output (SIDO) bi-directional buck-boost direct current (DC) to DC (DC-DC) converters. Various embodiments may provide a method for controlling a buck duty cycle buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter such that a first voltage measured across a first portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than a voltage of a first load and a second voltage measured across a second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than a voltage of a second load.

An embodiment includes a method for controlling a non-isolated SIDO bi-directional buck-boost DC-DC converter connected to a DC source, a first load, and a second load. The method includes determining a first voltage of the first load; determining a second voltage of the second load. The method includes controlling a buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter such that a first voltage measured across a first portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than the first voltage of the first load and a second voltage measured across a second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than the second voltage of the second load.

In another embodiment, a non-isolated SIDO bi-directional buck-boost DC-DC converter is disclosed. The non-isolated SIDO bi-directional buck-boost DC-DC converter includes a first input terminal configured to connect to a positive terminal of a DC source. The non-isolated SIDO bi-directional buck-boost DC-DC converter further includes a second input terminal configured to connect to a negative terminal of the DC source, a first controllable switch including a respective first side, and a second side. The first side of the first controllable switch is connected to the first input terminal. A second controllable switch includes a respective first side and a second side. The first side of the second controllable switch is connected to the second side of the first controllable switch and the second side of the second controllable switch is connected to the second input terminal. Further, the non-isolated SIDO bi-directional buck-boost DC-DC converter includes a first inductor having a respective first side and a second side. The first side of the first inductor is connected to the second side of the first controllable switch and the first side of the second controllable switch. The non-isolated SIDO bi-directional buck-boost DC-DC converter includes a third controllable switch having a respective first side and a second side. The first side of the third controllable switch is connected to the second side of the first inductor. A fourth controllable switch includes a respective first side and a second side. The first side of the fourth controllable switch is connected to the second side of the third controllable switch. Further, a second inductor includes a respective first side and a second side. The first side of the second inductor is connected to the second side of the fourth controllable switch and the second side of the second inductor is connected to the second side of the second controllable switch and the second input terminal. A fifth controllable switch includes a respective first side and a second side. The second side of the fifth controllable switch is connected to the second side of the first inductor and the first side of the third controllable switch. A sixth controllable switch includes a respective first side and a second side. The first side of the sixth controllable switch is connected to the second side of the fourth controllable switch and the first side of the second inductor. A first voltage output circuit portion includes a respective first side and a second side. The first side of the first voltage output circuit portion is connected to the second side of the fifth controllable switch. The first voltage output circuit portion is configured to output a first DC voltage to a first load. A second voltage output circuit portion includes a respective first side and a second side. The second side of the first voltage output circuit portion, the first side of the second voltage output circuit portion, the second side of the third controllable switch, and the first side of the fourth controllable switch are connected together. The second side of the second voltage output circuit portion is connected to the second side of the sixth controllable switch. Further, the second voltage output circuit portion is configured to output a second DC voltage to a second load. The non-isolated SIDO bi-directional buck-boost DC-DC converter includes a controller connected to the first controllable switch, the second controllable switch, the third controllable switch, the fourth controllable switch, the fifth controllable switch, and the sixth controllable switch. The controller is configured to at least control the first controllable switch and the second controllable switch according to a main duty cycle. The controller is configured to control the third controllable switch and the fifth controllable switch according to a first boost control duty cycle based at least in part on the main duty cycle. Further, the controller is configured to control the fourth controllable switch and the sixth controllable switch according to a second boost control duty cycle based at least in part on the main duty cycle. The controller is configured to control the main duty cycle, the first boost control duty cycle, and the second boost control duty cycle such that when the first load is greater than the second load the first boost control duty cycle is greater than the second boost control duty cycle and when the second load is greater than the first load the second boost control duty cycle is greater than the first boost control duty cycle.

In another embodiment a non-isolated SIDO bi-directional buck-boost DC-DC converter is disclosed. The non-isolated SIDO bi-directional buck-boost DC-DC converter includes a first input terminal configured to connect to a positive terminal of a DC source and a second input terminal configured to connect to a negative terminal of the DC source. A first capacitor includes a respective first side and a second side. The first side of the first capacitor is connected to the first input terminal. A second capacitor includes a respective first side and a second side. The first side of the second capacitor is connected to the second side of the first capacitor and the second side of the second capacitor is connected to the second input terminal. A first controllable switch includes a respective first side and a second side. The first side of the first controllable switch is connected to the first input terminal and the first side of the first capacitor. A second controllable switch includes a respective first side and a second side. The first side of the second controllable switch is connected to the second side of the first controllable switch and the second side of the second controllable switch is connected to the second input terminal. A first inductor includes a respective first side and a second side. The first side of the first inductor is connected to the second side of the first controllable switch and the first side of the second controllable switch. A third controllable switch includes a respective first side and a second side. The first side of the third controllable switch is connected to the second side of the first inductor. A fourth controllable switch includes a respective first side and a second side. The first side of the fourth controllable switch is connected to the second side of the third controllable switch. A second inductor includes a respective first side and a second side. The first side of the second inductor is connected to the second side of the fourth controllable switch and the second side of the second inductor is connected to the second side of the second controllable switch, the second input terminal, and the second side of the second capacitor. A fifth controllable switch includes a respective first side and a second side. The second side of the fifth controllable switch is connected to the second side of the first inductor and the first side of the third controllable switch. A sixth controllable switch includes a respective first side and a second side. The first side of the sixth controllable switch is connected to the second side of the fourth controllable switch and the first side of the second inductor. A first voltage output circuit portion includes a respective first side and a second side. The first side of the first voltage output circuit portion is connected to the second side of the fifth controllable switch. The first voltage output circuit portion is configured to output a first DC voltage to a first load. A second voltage output circuit portion includes a respective first side and a second side. The second side of the first voltage output circuit portion, the first side of the second voltage output circuit portion, the second side of the third controllable switch, the first side of the fourth controllable switch, the second side of the first capacitor, and the first side of the second capacitor are connected together. The second side of the second voltage output circuit portion is connected to the second side of the sixth controllable switch. The second voltage output circuit portion is configured to output a second DC voltage to a second load. The non-isolated SIDO bi-directional buck-boost DC-DC converter further includes a controller connected to the first controllable switch, the second controllable switch, the third controllable switch, the fourth controllable switch, the fifth controllable switch, and the sixth controllable switch. The controller is configured to at least control the first controllable switch and the second controllable switch according to a main duty cycle and control the third controllable switch and the fifth controllable switch according to a first boost control duty cycle based at least in part on the main duty cycle. The controller is configured to control the fourth controllable switch and the sixth controllable switch according to a second boost control duty cycle based at least in part on the main duty cycle. The controller is configured to control the main duty cycle, the first boost control duty cycle, and the second boost control duty cycle such that a first control voltage measured across the first inductor and the third controllable switch is maintained at less than the first DC voltage and a second control voltage measured across the second capacitor is maintained at less than the second DC voltage.

In yet another embodiment a power generation system is disclosed. The power generation system includes a DC source, a first load, a second load, and a non-isolated SIDO bi-directional buck-boost DC-DC converter connected to the DC source, the first load, and the second load. The non-isolated SIDO bi-directional buck-boost DC-DC converter includes a controller configured to control operation of the non-isolated SIDO bi-directional buck-boost DC-DC converter according to any of the methods above and/or wherein the SIDO buck-boost DC-DC converter is the SIDO buck-boost DC-DC converter of any of the above embodiments. In various embodiments, the DC source is a solid oxide fuel cell (SOFC) system.

The figures referred to in this description depict embodiments of the disclosure for the purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the systems and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

Overview

Various embodiments of the present disclosure provide a power system. The power system includes a direct current (DC) source that communicates with two downstream loads and/or devices through a non-isolated single-input dual-output (SIDO) bi-directional buck-boost DC to DC (DC-DC) converter. In various embodiments, a non-isolated SIDO bi-directional buck-boost DC-DC converter may be controllable to output DC voltage from the DC source to the two downstream loads in an equal or unequal manner. In various embodiments, the duty cycle of a non-isolated SIDO bi-directional buck-boost DC-DC converter may be controlled as a function of load power when the power demands of the two downstream loads and/or devices are unequal. Various embodiments may provide a method for controlling a buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter such that a first voltage measured across a first portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than a voltage of a first load and a second voltage measured across a second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than a voltage of a second load. In one embodiment, the DC source may be a DC power source, such as a fuel cell system, a photovoltaic system, a thermoelectric system, etc.

Various example embodiments of the present disclosure are described hereinafter with reference toFIG.1toFIGS.7A-7D.

FIG.1illustrates an exemplary modular fuel cell system described in U.S. Pat. No. 8,440,362, incorporated herein by reference in its entirety. The modular system may contain modules and components described above as well as in U.S. Pat. No. 9,190,693 issued on Nov. 17, 2015, and entitled “Modular Fuel Cell System” which is incorporated herein by reference in its entirety. The modular design of the fuel cell system enclosure10provides flexible system installation and operation.

The modular fuel cell system enclosure10includes a plurality of power module housings12(containing a fuel cell power module components), one or more fuel input (i.e. fuel processing) module housings16, and one or more power conditioning (i.e. electrical output) module housings18. For example, the system enclosure10may include any desired number of modules, such as 2-30 power modules, for example, 6-12 power modules.FIG.1illustrates a system enclosure10containing six power modules (one row of six modules stacked side to side), one fuel processing module, and one power conditioning module, on a common base20. Each module may comprise its own cabinet or housing. Alternatively, the power conditioning and fuel processing modules may be combined into a single input/output module located in one cabinet or housing14. For brevity, each housing12,14,16,18will be referred to as a “module” below.

While one row of power modules12is shown, the system may comprise more than one row of power modules12. For example, the system may comprise two rows of power modules stacked back to back.

Each power module12is configured to house one or more hot boxes13. Each hot box contains one or more stacks or columns of fuel cells (not shown for clarity), such as one or more stacks or columns of solid oxide fuel cells having a ceramic oxide electrolyte separated by conductive interconnect plates. Other fuel cell types, such as PEM, molten carbonate, phosphoric acid, etc. may also be used.

The modular fuel cell system enclosure10also contains one or more input or fuel processing modules16. The fuel processing modules16include a cabinet which contains the components used for pre-processing of fuel, such as desulfurizer beds. The fuel processing modules16may be designed to process different types of fuel. For example, a diesel fuel processing module, a natural gas fuel processing module, and an ethanol fuel processing module may be provided in the same or in separate cabinets. A different bed composition tailored for a particular fuel may be provided in each fuel processing module16. The fuel processing modules16may process at least one of the following fuels selected from natural gas provided from a pipeline, compressed natural gas, methane, propane, liquid petroleum gas, gasoline, diesel, home heating oil, kerosene, JP-5, JP-8, aviation fuel, hydrogen, ammonia, ethanol, methanol, syngas, biogas, bio-diesel, and other suitable hydrocarbon or hydrogen-containing fuels. If desired, a reformer17may be located in the fuel processing module16. Alternatively, if it is desirable to thermally integrate the reformer17with the fuel cell stack(s), then a separate reformer17may be located in each hot box13in the respective power module12. Furthermore, if internally reforming fuel cells are used, then an external reformer (such as the reformer17) may be omitted entirely.

The modular fuel cell system enclosure10also contains one or more power conditioning modules18. The power conditioning module18includes a cabinet that contains the components for converting the fuel cell stack generated DC power to AC power, electrical connectors for AC power output to the grid, circuits for managing electrical transients, a system controller (e.g., a computer or dedicated control logic device or circuit). The power conditioning module18may be designed to convert DC power from the fuel cell modules to different AC voltages and frequencies. Designs for 208V, 60 Hz; 480V, 60 Hz; 415V, 50 Hz, and other common voltages and frequencies may be provided.

The fuel processing module16and the power conditioning module18may be housed in one input/output cabinet14. If a single input/output cabinet14is provided, then the modules16and18may be located vertically (e.g., power conditioning module18components above the fuel processing module16desulfurizer canisters/beds) or side by side in the cabinet14.

As shown in one exemplary embodiment inFIG.1one input/output cabinet14is provided for one row of six power modules12, which are arranged linearly side to side on one side of the input/output module14. The row of power modules may be positioned, for example, adjacent to a building for which the system provides power (e.g., with the backs of the cabinets of the modules facing the building wall). While one row of the power modules12is shown, the system may comprise more than one row of power modules12. For example, as noted above, the system may comprise two rows of power modules stacked back to back.

Each of the power modules12and the input/output modules14includes a door30(e.g., hatch, access panel, etc.) to allow the internal components of the module to be accessed (e.g., for maintenance, repair, replacement, etc.). According to one embodiment, the power modules12and14are arranged in a linear array that has doors30only on one face of each cabinet, allowing a continuous row of systems to be installed abutted against each other at the ends. In this way, the size and capacity of the fuel cell enclosure10can be adjusted with the additional power modules12or14and the bases20with minimal rearranging needed for the existing power modules12and14and the bases20. If desired, the door30to the power module14may be on the side rather than on the front of the cabinet.

FIG.2illustrates a plan view of a fuel cell system hotbox13including a fuel cell stack or column40. The hotbox13is shown to include the fuel cell stack or the column40. However, the hotbox13may include two or more stacks or the columns40. The stack or column40may include the electrically connected fuel cells45stacked on one another, with interconnects50disposed between the fuel cells45. The first and last fuel cells45in the stack or column are disposed between a respective end plate60and the interconnect50. The end plates60are electrically connected to electrical outputs of the fuel cell stack or column40. The hotbox13may include other components, such as fuel conduits, air conduits, seals, electrical contacts, etc., and may be incorporated into a fuel cell system including balance of plant components. The fuel cells45may be solid oxide fuel cells containing a ceramic electrolyte, such as yttria stabilized zirconia (YSZ) or scandia stabilized zirconia (SSZ), an anode electrode, such as a nickel-YSZ, a Ni-SSZ or a nickel-samaria doped ceria (SDC) cermet, and a cathode electrode, such as lanthanum strontium manganite (LSM)). The interconnects50and/or the end plates60may include any suitable gas impermeable and electrically conductive material, such as a chromium-iron alloy, such as an alloy containing 4 to 6 wt % iron and balance chromium. The interconnects50electrically connect the adjacent fuel cells45and provide channels for fuel and air to reach the fuel cells45.

FIG.3shows a simplified diagram of a fuel cell power generation system300according to embodiments. As shown inFIG.3, the system300may include an Input/Output Module (IOM)310, a fuel cell system (such as a SOFC system)320, DC-DC converter330a, such as a non-isolated SIDO bi-directional buck-boost DC-DC converter, and two loads350, and360. The loads350, and360may include any device or group of devices meant to draw power from SOFC system320, such as an uninterruptible power system (UPS), a “micro-grid,” various computers or and/or servers (e.g., servers arranged in a server farm), electromechanical devices, lighting fixtures, climate control systems, etc. The loads350, and360may also be optionally separately connected to other components (including the grid301, alternative power supplies, batteries, etc.) so that the loads350, and360may optionally draw power when the SOFC system320is providing less power than required by the loads350, and360. If the loads350, and360are DC loads, then they may be directly electrically connected to the DC-DC converter330a. If the loads350, and360are alternating current (AC) loads, then a DC-AC inverter may be located between the DC-DC converter330aoutput and the input of the loads350, and360.

The IOM310may connect the SOFC system320to the power grid301. The IOM310can include an inverter310a, as shownFIG.3A, for converting a DC output from the SOFC system320to AC for use by the power grid301. The IOM310can also include other suitable components (not shown) including, but not limited to, controllers, resistive load banks, circuit breakers, and relays. It is to be understood that the IOM310is optional, as is connecting the fuel cell system320to the grid301. It is to be further understood that the features or components of the IOM310may be incorporated into other components, such as the fuel cell system320.

The fuel cell system320is shown inFIG.3Ato include a generalized power source320afor the sake of convenience. The fuel cell system320and/or the power source320amay include, for example, the SOFC system shown inFIG.1which contains the hot box13shown inFIGS.1and2. For the sake of brevity, the fuel cell system320is referred to below as “the SOFC system320”. However, it should be understood that the fuel cell system320may include other types of fuel cells, such as PEM fuel cells, molten carbonate fuel cells, etc. The SOFC system320may also include a number of other suitable components (not shown), such as energy storage devices (e.g., batteries or supercapacitors), fuel valves, fuel and air blowers, circuit breakers, temperature gauges, etc.

The SOFC system320may include a controller320b(as shown inFIG.3A). The controller320bmay include any suitable logic that can control certain aspects of the SOFC system320and/or the power source320a. For example, the controller320bmay control the fuel flow rate into the SOFC system, the output voltage from the SOFC system, air flow rate into the SOFC system, and fuel recycling rate in the SOFC system, etc. For example, the controller320bmay control the output voltage and/or power of SOFC system320to other components of the system300, such as to the IOM310and/or the DC-DC converter330a. In addition, the controller320bmay communicate, either directly or indirectly, with other components in the system300and/or with remote control terminals.

The DC-DC converter330amay provide DC voltage output from the SOFC system320at a higher and/or lower voltage compatible with the loads350, and360. As shown inFIG.3A, the DC-DC converter330amay also include a controller330b. The controller330bmay be similar to the controller320b, as described above in context of the SOFC system320, and may perform some similar functions as controller320b, as appropriate for the DC-DC converter330a. Alternatively, a single controller may control both the SOFC system320and the DC-DC converter330a. The controller330bmay be connected to various components of the DC-DC converter330a. The controller330bmay communicate indirectly with other components, such as the controller320b, the loads350, and360, etc., via parameters, such as an output voltage of the SOFC system320, the resistance of the loads350, and360, the voltage draw of the loads350, and360, etc. In various embodiments, the controller330bmay control one or more controllable switches (e.g., thyristors, field effect transistors, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), junction field effect transistors (JFETs) or metal-semiconductor field effect transistors (MESFETs), bipolar transistors, insulated-gate bipolar transistors, series connected MOSFETs (e.g., CMOS), relays, thyristor emulators, and/or diodes in series with insulated-gate bipolar transistors) of the DC-DC converter330ato regulate the voltage output to the loads350, and360. For example, the controller330bmay control the duty cycles of the controllable switches to control a buck duty cycle of the DC-DC converter330a.

In various embodiments, the DC-DC controller330amay be a non-isolated SIDO bi-directional buck-boost DC-DC converter, such as a non-isolated SIDO bi-directional buck-boost DC-DC converter400illustrated inFIG.4. The non-isolated SIDO bi-directional buck-boost DC-DC converter400may include various controllable switches402,404,407,410,412,414. While illustrated as MOSFET419and diode403pairs inFIG.4, the controllable switches402,404,407,410,412, and414may be any type controllable switch and are not limited to the MOSFET419and the diode403pairs. The controllable switches402,404,407,410,412, and414may include any controllable switching architecture, such as thyristors, field effect transistors, such as metal-oxide-semiconductor field-effect transistors (MOSFETs), junction field effect transistors (JFETs) or metal-semiconductor field effect transistors (MESFETs), bipolar transistors, insulated-gate bipolar transistors, series-connected MOSFETs (e.g., CMOS), relays, thyristor emulators, and/or diodes in series with insulated-gate bipolar transistors, etc. Additionally, while illustrated as being of the same type, controllable switches402,404,407,410,412, and414may be various combinations of different type of switches. Each controllable switch402,404,407,410,412, and414may have a respective first side and a second side. Each controllable switch402,404,407,410,412, and414may be opened to prevent current flow across that controllable switches402,404,407,410,412, and414from one side of the controllable switch402,404,407,410,412, and414to the other side of the controllable switch402,404,407,410,412, and414. Opening the controllable switch402,404,407,410,412, and414may be referred to as turning the controllable switch402,404,407,410,412, and414to an “OFF” state (or deactivated state) in which current does not flow. Each controllable switch402,404,407,410,412, and414may be closed to allow current flow across that controllable switch402,404,407,410,412, and414from one side of the controllable switch402,404,407,410,412, and414to the other side of the controllable switch402,404,407,410,412, and414. Closing the controllable switch402,404,407,410,412, and414may be referred to as turning the controllable switch402,404,407,410,412, and414to an “ON” state (or activated state) in which current does flow. The percentage of time that a controllable switch402,404,407,410,412, and414is in the “ON” state (or activated state) for a time period may be referred to as the duty cycle of the controllable switch402,404,407,410,412, and414.

The controllable switches402,404,407,410,412, and414may be connected to a controller450(for example the controller330bdescribed above). The controller450may be configured to control the controllable switches402,404,407,410,412, and414according to various duty cycles, such as a main duty cycle “D”, a first boost control duty cycle “D1”, and a second boost control duty cycle “D2”. In various embodiments, the different duty cycles, such as the main duty cycle “D”, the first boost control duty cycle “D1”, and the second boost control duty cycle “D2”, may be determined and/or adjusted by the controller450to control the buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter400. While illustrated as a single control unit, the controller450may be one or more separate control units in communication operating together to control the buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter400by determining and/or adjusting the different duty cycles, such as the main duty cycle “D”, the first boost control duty cycle “D1”, and the second boost control duty cycle “D2”.

The non-isolated SIDO bi-directional buck-boost DC-DC converter400may include a first input terminal401aconfigured to connect to a positive terminal of a DC source, such as the SOFC system320. The non-isolated SIDO bi-directional buck-boost DC-DC converter400may include a second input terminal401bconfigured to connect to a negative terminal of the DC source, such as the SOFC system320. The controllable switch402may be connected on one side to the first input terminal401aand on the other side to the controllable switch404and the inductor406. The controllable switch404may be connected on one side to the controllable switch402and the inductor406to the second input terminal401band the inductor409. The inductor406may be connected on one side to the controllable switch402and the controllable switch404and on the other side to the controllable switch407and the controllable switch412. The inductor409may be connected on one side to the controllable switch404and the second input terminal401bto the controllable switch410and the controllable switch414.

The non-isolated SIDO bi-directional buck-boost DC-DC converter400may include a first voltage output circuit portion417associated with the load350and a second voltage output circuit portion429associated with the load360. The loads350, and360are represented by resistors/resistances “R1” and “R2”, respectively, in the illustration of the non-isolated SIDO bi-directional buck-boost DC-DC converter400. The first voltage output circuit portion417and the second voltage output circuit portion429may include their own respective capacitors416, and418connected in parallel with the loads350, and360. The first voltage output circuit portion417and the second voltage output circuit portion429may connect with one another. One side of the first voltage output circuit portion417may connect to the controllable switch412and the other side of the first voltage output circuit portion417may connect to the controllable switch407, the controllable switch410, and the second voltage output circuit portion429. One side of the second voltage output circuit portion429may connect to the controllable switch414and the other side of the second voltage output circuit portion429may connect to the controllable switch407, the controllable switch410, and the first voltage output circuit portion417. The first voltage output circuit portion417may output a DC voltage to the load350and the second voltage output circuit portion429may output a DC voltage to the load360. The controller450may receive various parameters (e.g., measurements, indications, etc.) from points in the non-isolated SIDO bi-directional buck-boost DC-DC converter400and/or the system300, such as the load350, and360voltages, resistances, currents, and/or powers, the voltage, resistance, current, and/or power output of the SOFC system320, the voltage and/or current measurements at or across one or more of the controllable switches402,404,407,410,412, and414, and/or the inductors406, and409, or any other parameters. Such parameters may be received from sensing or measuring devices installed in the non-isolated SIDO bi-directional buck-boost DC-DC converter400and/or the system300. The controller450may communicate instructions (i.e. apply voltages) to the gate electrodes of the transistors419of the controllable switches402,404,407,410,412, and414via a wired or wireless connection (labeled by letters A to F inFIG.4) to turn the controllable switches402,404,407,410,412and/or414ON or OFF.

The controllable switch402and the controllable switch404may be controlled according to the main duty cycle “D”. For example, the controllable switch402may be controlled by the controller450to have a duty cycle corresponding to the main duty cycle “D” and the controllable switch404may be controlled by the controller450to have a duty cycle of 1 minus the main duty cycle “D” (i.e. 1−D).

The controllable switch407and the controllable switch412may be controlled according to the first boost control duty cycle “D1” associated with the load350. For example, the controllable switch407may be controlled by the controller450to have a duty cycle corresponding to the first boost control duty cycle “D1” and the controllable switch412may be controlled by the controller450to have a duty cycle of 1 minus the first boost control duty cycle “D1” (i.e. 1−D1).

The controllable switch410and the controllable switch414may be controlled according to the second boost control duty cycle “D2” associated with the load360. For example, the controllable switch410may be controlled by the controller450to have a duty cycle corresponding to the second boost control duty cycle “D2” and the controllable switch414may be controlled by the controller450to have a duty cycle of 1 minus the second boost control duty cycle “D2” (i.e. 1−D2).

In various embodiments, the controller450may control the main duty cycle “D”, the first boost control duty cycle “D1”, and the second boost control duty cycle “D2” such that when the load350is greater than the load360(i.e. when the voltage V1 drawn by the load350is greater than the voltage V2 drawn by the load360), the first boost control duty cycle “D1” is greater than the second boost control duty cycle “D2” and when the load360is greater than the load350(i.e. when the voltage V1 drawn by the load350is less than the voltage V2 drawn by the load360), the second boost control duty cycle “D2” is greater than the first boost control duty cycle “D1”.

In the non-isolated SIDO bi-directional buck-boost DC-DC converter400, the voltage output “V1” to load350may be determined and controlled by the controller450according to the equation:

V⁢1=V×D1-D⁢1·1(1+k2×R⁢1R⁢2)=V×D1-D⁢1·R⁢2(R⁢2+R⁢2×k2×R⁢1)where “k” is a voltage constant relating the voltage output “V1” to the load350and voltage output “V2” to the load360such that V1=V2/k, and “V” is the voltage output “V” of the source, such as the SOFC system320. As the resistance “R2” of the load360approaches infinity (i.e. the load360goes to a no-load condition or moves toward stopping drawing power from the SOFC system320, stated another way R2→∞), the voltage output “V1” to the load350may be determined and controlled by the controller450according to the equation:

The maximum input voltage “maxV” that can be applied to the split boost without losing controllability (output of buck) may be when the first boost control duty cycle “D1” is zero and determined and controlled by the controller450according to the equation:

To effectively utilize the boost, the buck duty cycle (or main duty cycle “D”) may be controlled by the controller450such that until the input voltage to the boost reaches this maximum input voltage “maxV”, the buck duty cycle (or main duty cycle “D”) is maintained at 1.

In a similar manner, in the non-isolated SIDO bi-directional buck-boost DC-DC converter400, the voltage output “V2” to the load360may be determined and controlled by the controller450according to the equation:

V⁢2=V×D1-D⁢2·1(1+R⁢2R⁢1×k2)=V×D1-D⁢2·R⁢1×k2(R⁢1×k2+R⁢2)where “k” is the voltage constant relating the voltage output “V2” to the load360and voltage output “V1” to load350such that V2=V1*k, and “V” is the voltage output “V” of the source, such as the SOFC system320. As the resistance “R1” of load350approaches infinity (i.e. load350goes to a no-load condition or moves toward stopping drawing power from the SOFC system320, stated another way R→∞), the voltage output “V2” to load360may be determined and controlled by the controller450according to the equation:

The control parameter duty cycles that are the first boost control duty cycle “D1” and the second boost control duty cycle “D2” may be determined and controlled by the controller450by the respective equations:

In various embodiments, the controller450may be configured such that for normalized voltage output “V1” to the load350and voltage output “V2” to the load360, if “R2” is greater than “R1” then “D2” may be greater than “D1”, and, similarly, if “R1” is greater than “R2” then “D1” may be greater than “D2”. The controller450may be configured such that the control duty cycle may be a function of load power when the loads350, and360are unequal. Also, the direction of control change may depend on how the loads350, and360are distributed, such as equally distributed or unequally distributed. As the resistance “R2” of the load360approaches infinity (i.e. the load360goes to a no-load condition or moves toward stopping drawing power from the SOFC system320, stated another way R2→∞, the controller450may be configured such that the second boost control duty cycle “D2” moves toward1(or stated another way D2→1. As the resistance “R1” of the load350approaches infinity (i.e. load350goes to a no-load condition or moves toward stopping drawing power from the SOFC system320, stated another way R1→∞, the controller450may be configured such that the first boost control duty cycle “D1” moves toward1(or stated another way D1→1).

The non-isolated SIDO bi-directional buck-boost DC-DC converter400may be configured to measure a voltage across the inductor406and the controllable switch407as the voltage “Va”, the voltage across the inductor409and the controllable switch410as the voltage “Vb”. The voltage “Va” and/or voltage “Vb” may be provided to the controller450and used for controlling the operation of the non-isolated SIDO bi-directional buck-boost DC-DC converter400.

FIG.5illustrates an alternative configuration of a non-isolated SIDO bi-directional buck-boost DC-DC converter500according to an embodiment that may be used as the DC-DC controller330a. The non-isolated SIDO bi-directional buck-boost DC-DC converter500may be similar to the non-isolated SIDO bi-directional buck-boost DC-DC converter400ofFIG.4, except that capacitors502and503may be connected to one another and connected to the controllable switch407, the controllable switch410, the first voltage output circuit portion417, and the second voltage output circuit portion429. The capacitor502may also be connected to the first input terminal401aand the controllable switch402. The capacitor503may also be connected to the second input terminal401b, the controllable switch404, and the inductor409. In addition to the measurements and sensing discussed above for the non-isolated SIDO bi-directional buck-boost DC-DC converter400, the non-isolated SIDO bi-directional buck-boost DC-DC converter500may be configured to measure a voltage across the inductor406and the controllable switch407as the voltage “Va”, the voltage across the capacitor503as the voltage “Vb”, and the voltage across the capacitor502as the voltage “Vc”. The voltage “Va”, voltage “Vb”, and/or voltage “Vc” may be provided to the controller450and used for controlling the operation of the non-isolated SIDO bi-directional buck-boost DC-DC converter500.

In the non-isolated SIDO bi-directional buck-boost DC-DC converter500, the DC voltages “Va” and “Vb” may be determined by the controller450according to the equations:

Vb=V×D1·k2×R⁢1(R⁢2+k2×R⁢1)andVa=V×D-Vb=V×D-V×D1·k2×R⁢1(R⁢2+k2×R⁢1)
where “k” is the voltage constant relating the voltage output “V2” to the load360and voltage output “V1” to the load350such that V2=V1*k, “V” is the voltage output “V” of the source, such as the SOFC system320, “R1” is the resistance of the load350, and “R2” is the resistance of the load360.

The controller450may be configured such that the main duty cycle “D” is controlled such that “Va” is always less than or equal to “V1”. Similarly, the controller450may be configured such that the main duty cycle “D” is also controlled such that “Vb” is always less than or equal to “V2”. As such, the controller450may be configured such that the main duty cycle “D” is maintained at a value that ensures “Va” is less than “V1” and “Vb” is less than “V2”. The main duty cycle “D” being maintained at a value that ensures “Va” is less than “V1” and “Vb” is less than “V2” may provide a highest efficiency and one stage of power conversion for the non-isolated SIDO bi-directional buck-boost DC-DC converter500. Reference tracking and min/max controllers may be used to achieve these conditions (e.g., the main duty cycle “D” being maintained at a value that ensures “Va” is less than “V1” and “Vb” is less than “V2”) as the values of “V1” and “V2” may be mutually exclusive. There may be a unique solution of the main duty cycle “D” that may achieve max efficiency and minimum power conversion for any given “V1” and “V2”.

FIGS.6A-6D, collectively, represent process flow diagrams illustrating methods600,610,620, and630for controlling a buck duty cycle of a non-isolated SIDO bi-directional buck-boost DC-DC converter, such as the non-isolated SIDO bi-directional buck-boost DC-DC converter400, and500, according to various embodiments. In various embodiments, the operations of the methods600,610,620, and630may be performed by a controller (e.g., the controller330b, and450).

With reference to the method600ofFIG.6A, in block602, the controller may perform operations including determining a first voltage of the first load. For example, the controller may determine the voltage “V1” of the load350.

In block604, the controller may perform operations including determining a second voltage of the second load. For example, the controller may determine the voltage “VT” of the load360.

In block606, the controller may perform operations including controlling a buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter such that a first voltage measured across a first portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained less than the first voltage of the first load and a second voltage measured across a second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter is maintained at less than the second voltage of the second load. For example, the controller may control the main duty cycle “D” of the non-isolated SIDO bi-directional buck-boost DC-DC converter such that the voltage “Va” measured across the controllable switch407and inductor406is maintained at less than the voltage “V1” of the load350and the voltage “Vb” across the capacitor503is maintained at less than the voltage “VT” of the load360.

FIG.6Billustrates a method610that may be performed by a controller (e.g., controller330b,450) to control the buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter in block606of method600.

With reference to the method610ofFIG.6B, in block612, the controller may perform operations including determining a main duty cycle value “D1” based at least in part on the first voltage of the first load (e.g., “V1”) and the second voltage of the second load (e.g., “V2”), wherein the duty cycle value achieves a maximum efficiency for the non-isolated SIDO bi-directional buck-boost DC-DC converter and a minimum power conversion. Determining the main duty cycle value “D1” based at least in part on the first voltage of the first load (e.g., “V1”) and the second voltage of the second load (e.g., “V2”) may include determining the main duty cycle value “D1” based at least in part on the first voltage of the first load (e.g., “V1”), the second voltage of the second load (e.g., “V2”), the first voltage measured across the first portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter (e.g., “Va”), and the second voltage measured across the second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter (e.g., “Vb”). Determining the main duty cycle value “D1” based at least in part on the first voltage of the first load (e.g., “V1”) and the second voltage of the second load (e.g., “V2”) may include determining the main duty cycle value “D1” based at least in part on the first voltage of the first load (e.g., “V1”), the second voltage of the second load (e.g., “V2”), the second voltage measured across the second portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter (e.g., “Vb”), and a third voltage measured across a third portion of the non-isolated SIDO bi-directional buck-boost DC-DC converter (e.g., “V c”).

In block614, the controller may perform operations including setting the buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter to the determined main duty cycle value “D1”.

FIG.6Cillustrates the method620that may be performed by a controller (e.g., the controller330b,450) to control the buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter in block606of the method600.

With reference to the method620ofFIG.6C, in block622, the controller may perform operations including determining a first boost control duty cycle “D1” associated with the first load (e.g., the load350) based at least in part on the first voltage of the first load (e.g., “V1”) and a difference between the first voltage of the first load (e.g., “V1 of the load350”) and the second voltage of the second load (e.g., “V2” of the load360).

In block624, the controller may perform operations including determining a second boost control duty cycle “D2” associated with the second load (e.g., the load360) based at least in part on the second voltage of the second load (e.g., “V2 of the load360”) and the difference between the first voltage of the first load (“V1 of the load350”) and the second voltage of the second load (“V2 of the load360”).

In block626, the controller may perform operations including controlling split boost portions of the non-isolated SIDO bi-directional buck-boost DC-DC converter according to the determined first boost control duty cycle “D1” and the determined second boost control duty cycle “D2”.

FIG.6Dillustrates the method630that may be performed by a controller (e.g., controller330b,450) to control the buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter in block606of method600.

With reference to the method630ofFIG.6D, in block632, the controller may perform operations including determining a positive control value as a result of the first voltage of the first load (e.g., “V1” of the load350) added to the second voltage of the second load (e.g., “V2” of the load360).

In block634, the controller may perform operations including determining a negative control value as a result of the second voltage of the second load (e.g., “V2” of the load360) subtracted from the first voltage of the first load (e.g., “V1” of the load350).

In block636, the controller may perform operations including determining a first boost control duty cycle “D1” associated with the first load (e.g., the load350) based at least in part on subtracting the negative control value from the positive control value.

In block638, the controller may perform operations including determining a second boost control duty cycle “D2” associated with the second load (e.g., the load360) based at least in part on adding the positive control value and the negative control value together.

In block640, the controller may perform operations including controlling split boost portions of the non-isolated SIDO bi-directional buck-boost DC-DC converter according to the determined first boost control duty cycle “D1” and the determined second boost control duty cycle “D2”.

FIGS.7A-7D, collectively, represent control logic diagrams illustrating example operations to control a buck duty cycle of the non-isolated SIDO bi-directional buck-boost DC-DC converter, such as non-isolated SIDO bi-directional buck-boost DC-DC converter400, and500, according to various embodiments.FIGS.7A-7Dillustrate specific arrangements of control modules702-754, such as difference controllers, reference tracking and saturation controllers, minimum/maximum (min/max) controllers, division controllers, etc. The specific arrangements of the control modules702-754inFIGS.7A-7Dmay represent example implementations of the methods600,610,620, and630for controlling a buck duty cycle of a non-isolated SIDO bi-directional buck-boost DC-DC converter, such as non-isolated SIDO bi-directional buck-boost DC-DC converter400, and500ofFIGS.6A-6D. In various embodiments, the control modules702-754may be implemented in hardware, software, and/or combinations of hardware and software.

FIG.7Aillustrates a control configuration for buck control outputting a main duty cycle “D”. A difference controller702outputs the difference between “Va” and a reference voltage “Vref1” which is less than or equal to “V1”. That value is output to a reference tracking controller with a saturation706which outputs the resulting value to a min/max controller710. A difference controller704outputs the difference between “Vb” and a reference voltage “Vref2” which is less than or equal to “V2”. That value is output to a reference tracking controller with a saturation708which outputs the resulting value to the min/max controller710. The min/max controller710then outputs the main duty cycle “D” that achieves the maximum efficiency and the minimum power conversion from the values output by reference tracking controllers with the saturation706, and708. The control method illustrated inFIG.7Amay maximize the efficiency of a non-isolated SIDO bi-directional buck-boost DC-DC converter, such as the non-isolated SIDO bi-directional buck-boost DC-DC converter400, and500while minimizing the loss of the non-isolated SIDO bi-directional buck-boost DC-DC converter.

FIG.7Billustrates another control configuration for buck control outputting a main duty cycle “D”. A controller720may divide “V1” by “Vc” and a controller722may divide “V2” by “Vb”. The resulting quotients from the controllers720, and722may be output to the to a min/max controller710. The min/max controller710then outputs the main duty cycle “D” that achieves the maximum efficiency and the minimum power conversion from the values output by the controllers720, and722.

FIG.7Cillustrates a control configuration for boost split output control that may operate with either of the configurations ofFIGS.7A and7B. In the configuration ofFIG.7C, one control chain of difference controller730and reference tracking controller with a saturation736controls “V1”, another control chain of difference control734and reference tracking controller with a saturation740controls “V2”, and a third control chain of difference controller732and reference tracking controller with a saturation738controls the difference between “V1” and “V2” and ensures control is achieved for unbalanced loads by adding or subtracting the output of the other control chains. Specifically, a reference voltage “Vref1” and the feedback voltage of “V1” are provided to the difference controller730and the result is fed to the reference tracking controller with the saturation736. A reference voltage “Vref2” and the feedback voltage of “V2” are provided to the difference controller734and the result is fed to the reference tracking controller with the saturation740. A reference voltage “(V1−V2) ref” and the feedback voltage of “(V1−V2)_fb” are provided to the difference controller732and the result is fed to the reference tracking controller with the saturation738. The output of the reference tracking controller with the saturation the738is subtracted from the output of the reference tracking controller with the saturation736by the difference controller742to generate the output for the first boost control duty cycle “D1”. The output of the reference tracking controller with the saturation738is added to the output of the reference tracking controller with the saturation740by the controller744to generate the output for the second boost control duty cycle “D2”.

FIG.7Dillustrates another control configuration for boost split output control that may operate with either of the configurations ofFIGS.7A and7B. In the configuration ofFIG.7C, the boost may be controlled through “V1” being added to “V2” and “V2” being subtracted from “V1”. A reference voltage “(V1+V2)_ref” and the feedback voltage of “(V1+V2)_fb” are provided to a difference controller750and the result is fed to the reference tracking controller with a saturation754. A reference voltage “(V1−V2)_ref” and the feedback voltage of “(V1−V2)_fb” are provided to the difference controller732and the result is fed to the reference tracking controller with the saturation738. The output of the reference tracking controller with the saturation754is subtracted from the output of the reference tracking controller with the saturation738by the difference controller742to generate the output for the first boost control duty cycle “D1”. The output of the reference tracking controller with the saturation754is added to the output of the reference tracking controller with the saturation738by the controller744to generate the output for the second boost control duty cycle “D2”.

As an example, of controlling a buck duty cycle of a non-isolated SIDO bi-directional buck-boost DC-DC converter, such as the non-isolated SIDO bi-directional buck-boost DC-DC converter400, and500, according to various embodiments, the “V” output by the source, such as the SOFC system320, may be 320-480 VDC. When “V1” may be 390 VDC and “V2” may be 390 VDC, the loads may be balanced and the main duty cycle “D1” may be 1 as buck may not be required. When the loads are unbalanced, such as the power “P1” of the load350is at a no load and the power “P2” of the load360is at 100%, and “V” reaches 400 VDC, the boost becomes uncontrolled as “Va” equals 0 VDC and “Vb” equals 400 VDC. To have control on boost, buck may be operated such that “Vb” will not exceed 390 VDC. The boost control may be set so that “D1” equals 1 and “D2” equals 0 with “D” equal to 0.975. Accordingly, the boost stops switching and the buck starts controlling “V2”. The buck control also ensures that unless “Vb” reaches 390 VDC, the buck will operate with “D” equal to 1 ensuring maximum efficiency with an unbalanced load. Similarly, for the other side load unbalance (e.g., where “Vb” equals 0 VDC and “Va” equals 400 VDC) buck will start controlling “V1”.

In an embodiment, the functions of the energy storage system, energy storage system technologies, and the energy storage system technologies management system may be implemented in software, hardware, firmware, on any combination of the foregoing. In an embodiment, the hardware may include circuitry designed for implementing the specific functions of the energy storage system, energy storage system technologies, and/or the energy storage system technologies management system. In an embodiment, the hardware may include a programmable processing device configured with instructions to implement the functions of the energy storage system, energy storage system technologies, and/or the energy storage system technologies management system.

The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the order of steps in the foregoing embodiments may be performed in any order. Further, words such as “thereafter,” “then,” “next,” etc. are not intended to limit the order of the steps; these words are simply used to guide the reader through the description of the methods.

One or more block/flow diagrams have been used to describe exemplary embodiments. The use of block/flow diagrams is not meant to be limiting with respect to the order of operations performed. The foregoing description of exemplary embodiments has been presented for purposes of illustration and of description. It is not intended to be exhaustive or limiting with respect to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosed embodiments. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Control elements may be implemented using computing devices (such as a computer) comprising processors, memory and other components that have been programmed with instructions to perform specific functions or may be implemented in processors designed to perform the specified functions. A processor may be any programmable microprocessor, microcomputer or multiple processor chip or chips that can be configured by software instructions (applications) to perform a variety of functions, including the functions of the various embodiments described herein. In some computing devices, multiple processors may be provided. Typically, software applications may be stored in the internal memory before they are accessed and loaded into the processor. In some computing devices, the processor may include internal memory sufficient to store the application software instructions.