Patent Publication Number: US-2022224331-A1

Title: Switching circuit

Description:
BACKGROUND 
     The field of the disclosure relates generally to switching circuits and, more particularly, to a switching circuit for a phase leg of a paralleled switching circuit. 
     Most known converter circuits include multiple switching circuits coupled in parallel between a first bus and a second bus, or between an input bus and an output bus. The switching circuits are generally controlled in a manner to produce a conversion, e.g., from direct current (DC) to alternating current (AC), from DC to DC, or from AC to DC. The inclusion of multiple switching circuits, or “phase legs,” in parallel generally increases the overall power capacity of, for example, the converter, or any other device within which the switching circuit is implemented. 
     There are at least two known implementations of switching circuits: device-in-parallel and converter-in-parallel. In a device-in-parallel circuit, the switching devices themselves, e.g., a power metal-oxide semiconductor field-effect transistor (MOSFET), are coupled in parallel between the first bus and the second bus, and the switching devices are controlled by a common gate driver, or gate driver circuit. In a converter-in-parallel circuit, the switching devices are integrated within a converter circuit, and multiple converter circuits are coupled in parallel between the first bus and the second bus. Each parallel converter is then operated independently, e.g., based on a feedback loop. Generally, some known switching circuits perform sufficiently on certain metrics considered in system, e.g., converter, design, including, for example, dynamic current sharing, complexity and cost of control, parasitics, circulating currents among paralleled devices, power derating, scalability, and contribution of noise to external circuits. It would be desirable to have a switching circuit for a phase leg of a converter circuit that improves on at least some of the above-mentioned metrics. 
     BRIEF DESCRIPTION 
     In one aspect, a switching circuit is provided. The switching circuit includes a first stage, a second stage, a decoupling inductor, a decoupling capacitor, and a semiconductor switch coupled between the first stage and the second stage. The first stage is configured to be coupled to a first bus. The second stage is configured to be coupled to a second bus. The decoupling inductor is coupled to the second stage, and the decoupling capacitor is coupled to the first stage. The semiconductor switch is configured to be controlled to convert a first current received at the first stage to a second current supplied to the second stage. 
     In another aspect, a paralleled switching circuit is provided. The paralleled switching circuit includes a first bus, a second bus, and a plurality of phase legs respectively coupled between the first bus and the second bus. The first bus is configured to supply a first current, and the second bus is configured to receive a second current. The plurality of phase legs each include a switching circuit configured to conduct a share of a total current supplied in the second current. The switching circuit includes a decoupling capacitor, a decoupling inductor, and a semiconductor switch coupled between the first bus and the second bus. The decoupling capacitor is coupled across the first bus. The decoupling inductor is coupled in series between the semiconductor switch and the second bus. The semiconductor switch is configured to be controlled to convert the first current to the second current. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a schematic block diagram of an exemplary paralleled switching circuit; and 
         FIG. 2  is a schematic diagram of paralleled switching circuits for use in the paralleled switching circuit shown in  FIG. 1 . 
     
    
    
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, a number of terms are referenced that have the following meanings. 
     The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it relates. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     Some embodiments involve the use of one or more electronic processing or computing devices. As used herein, the terms “processor” and “computer” and related terms, e.g., “processing device,” “computing device,” and “controller” are not limited to just those integrated circuits referred to in the art as a computer, but broadly refers to a processor, a processing device, a controller, a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a microcomputer, a programmable logic controller (PLC), a reduced instruction set computer (RISC) processor, a field programmable gate array (FPGA), a digital signal processing (DSP) device, an application specific integrated circuit (ASIC), and other programmable circuits or processing devices capable of executing the functions described herein, and these terms are used interchangeably herein. The above embodiments are examples only, and thus are not intended to limit in any way the definition or meaning of the terms processor, processing device, and related terms. 
     In the embodiments described herein, memory may include, but is not limited to, a non-transitory computer-readable medium, such as flash memory, a random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), and non-volatile RAM (NVRAM). As used herein, the term “non-transitory computer-readable media” is intended to be representative of any tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including, without limitation, volatile and non-volatile media, and removable and non-removable media such as a firmware, physical and virtual storage, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being a transitory, propagating signal. Alternatively, a floppy disk, a compact disc-read only memory (CD-ROM), a magneto-optical disk (MOD), a digital versatile disc (DVD), or any other computer-based device implemented in any method or technology for short-term and long-term storage of information, such as, computer-readable instructions, data structures, program modules and sub-modules, or other data may also be used. Therefore, the methods described herein may be encoded as executable instructions, e.g., “software” and “firmware,” embodied in a non-transitory computer-readable medium. Further, as used herein, the terms “software” and “firmware” are interchangeable, and include any computer program stored in memory for execution by personal computers, workstations, clients and servers. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. Furthermore, as used herein, the term “real-time” refers to at least one of the time of occurrence of the associated events, the time of measurement and collection of predetermined data, the time to process the data, and the time of a system response to the events and the environment. In the embodiments described herein, these activities and events occur substantially instantaneously. 
     Embodiments of the present disclosure relate to a switching circuit for a phase leg in, for example, a paralleled switching circuit or a converter. The switching circuit described herein provides a fully-decoupled phase leg that can be paralleled between a first bus and a second bus, such as between a DC bus and an AC bus or between two DC buses, for example. At least some embodiments of the switching circuit described herein include a decoupling inductor at a second stage to stabilize current output over time, e.g., to filter high-frequency noise at the second stage. At least some embodiments of the switching circuit described herein include a decoupling capacitor at a first stage to stabilize voltage input over time, e.g., to filter high-frequency noise at the first stage. Being fully-decoupled from the first and second buses enables a plurality of switching circuits based on the fully-decoupled phase leg circuit described herein to provide desirable levels of current sharing and reduces parasitics and circulating currents. Accordingly, such switching circuits are not subject to de-rating. At least some embodiments of the switching circuit described herein include a common gate driver for each same-positioned switch device of paralleled switching circuits. Switch devices may include, for example, a power semiconductor switch, power MOSFET, insulated gate bipolar transistor (IGBT), bipolar junction transistor (BJT), or other suitable switching device. Control of the switching circuit described herein is, accordingly, simple and cost effective. Embodiments of the switching circuit described herein are efficient and scalable, and contribute little noise to external circuits relative to device-in-parallel or converter-in-parallel alternatives, for example. 
       FIG. 1  is a schematic block diagram of an exemplary paralleled switching circuit  100 . Paralleled switching circuit  100  includes a first bus  102  and a second bus  104 . Paralleled switching circuit  100  includes a plurality of phase legs  106  respectively coupled in parallel between first bus  102  and second bus  104 , i.e., paralleled phase legs  106 . A first current, or input current, is supplied on first bus  102 , and a second current, or output current, is received, from phase legs  106  on second bus  104 , or vice versa. Each phase leg includes a switching circuit (not shown) configured to conduct a share of a total current supplied in the second current. In a balanced paralleled switching circuit, the respective shares of current conducted through phase legs  106  are substantially equal, e.g., no more than plus-or-minus 2.5% amplitude (amperes) from one phase leg  106  to another. The distribution of the total current through phase legs  106  is referred to as current sharing. Variations among components or in switching timing in phase legs  106 , circulating currents, or parasitic currents may result in uneven current sharing among phase legs  106 , which may further necessitate a de-rating of the total power capacity of paralleled switching circuit  100 . For example, for a paralleled switching circuit having two phase legs  106  each individually rated for 1.0 amperes, with uneven current sharing the total current rating for paralleled switching circuit  100  may be 1.8 amperes as opposed to 2.0 amperes in a balanced paralleled switching circuit. Embodiments of phase legs  106  described herein enable substantially equal current sharing due to synchronous control of phase legs  106 , stable current conduction by each phase leg due to a decoupling inductor, and reduction of circulating currents. 
     In certain embodiments, first bus  102  includes a DC bus having a positive DC line  108  and a negative DC line  110 . In such embodiments, paralleled switching circuit  100  may function as a DC-DC converter, e.g., a boost or buck converter, or a DC-AC converter, e.g., an inverter. In DC-DC applications, paralleled switching circuit  100  may step-up or step-down DC voltages for supplying, for example, DC power from a renewable source, such as a photovoltaic array, to an energy storage device, such as a battery. In DC-AC applications, paralleled switching circuit  100  may convert, for example, DC power from a battery or photovoltaic array to an AC power sufficient for supplying to an AC load, e.g., a motor, or an AC utility grid. 
     In certain embodiments, paralleled switching circuit  100  includes an energy storage capacitor  112  coupled across first bus  102 , e.g., across positive DC line  108  and negative DC line  110 . The capacitive value of energy storage capacitor  112  varies per application to provide sufficient power capacity for the given application. For example, in one embodiment, energy storage capacitor  112  includes one or more capacitors having a combined capacitance in a range of 100 microfarad to 100 millifarad. Generally, higher-power applications utilize greater energy storage capacitances. Energy storage capacitor  112  should have an operating frequency range, or “rated” frequency, around the switching frequency of paralleled switching circuit  100 . For example, paralleled switching circuit  100  may utilize a switching frequency in the range of 1 KiloHertz (KHz) to 100 KHz, and so energy storage capacitor  112  should be rated to operate at least in that frequency range of 1 KHz to 100 KHz. 
     In certain embodiments, second bus  104  is a DC output bus, e.g., for DC-DC applications. In alternative embodiments, second bus  104  is an AC line that supplies AC power to a load, such as, for example, a motor, electric grid, or any other suitable AC load. In certain such embodiments, paralleled switching circuit  100  further includes a line filter inductor  114  coupled in series with second bus  104 . Line filter inductor  114  is generally a large inductance configured to minimize harmonics presented to the load by paralleled switching circuit  100 , and are selected based on the power throughput for a given application. For example, in certain embodiments, line filter inductor  114  has an inductance in a range of 1 microhenry to 100 microhenry. 
     In certain embodiments, paralleled switching circuit  100  includes a current sensor  116  coupled to second bus  104  and configured to detect an amplitude of the second current conducted over second bus  104 . Current sensor  116 , in certain embodiments, provides a current measurement to a digital signal processor (DSP)  118  or other suitable processing device to enable control of total current conducted through paralleled switching circuit  100 . 
     Each of phase legs  106  includes a decoupling capacitor, one or more semiconductor switches, and a decoupling inductor (not shown).  FIG. 2  is a schematic diagram of paralleled switching circuits  200  for use in phase legs  106  of paralleled switching circuit  100  shown in  FIG. 1 . Each switching circuit  200  includes a first stage  202  coupled to first bus  102 , and a second stage  204  coupled to second bus  104 . Switching circuit  200  includes a decoupling capacitor  206  and a decoupling inductor  208 . Decoupling capacitor  206  is coupled to, or across, first stage  202  and, accordingly, across positive DC line  108  and negative DC line  110  of first bus  102 . Decoupling inductor  208  is coupled to second stage  204  and, more specifically, in series with second stage  204 . 
     Generally, switching circuit  200  includes at least one semiconductor switch coupled between first stage  202  and second stage  204 , and therefore between first bus  102  and second bus  104 . The semiconductor switches may be embodied in one or more power MOSFET, IGBT, or BJT, for example. As illustrated in  FIG. 2 , switching circuit  200  includes a first semiconductor switch  210  and a second semiconductor switch  212 , each coupled between first stage  202  and second stage  204 . More specifically, first semiconductor switch  210  is coupled between positive DC line  108  and a midpoint node  214  (located between first semiconductor switch  210  and second semiconductor switch  212 ), and second semiconductor switch  212  is coupled between negative DC line  110  and midpoint node  214 . First semiconductor switch  210  and second semiconductor switch  212  are configured to be controlled to convert a first current received over first stage  202  to a second current supplied to second stage  204  and to second bus  104 . 
     The semiconductor switches, such as first semiconductor switch  210  and second semiconductor switch  212 , in switching circuit  200  are generally operated, or commutated, at a selected frequency to produce a desired conversion of the first current at first stage  202  to the second current at second stage  204 . Likewise, in at least embodiments where paralleled switching circuit  100  is a DC-AC converter, first semiconductor switch  210  and second semiconductor switch  212  are coordinated, or commutated in an alternating manner, such that while one is open, the other is closed, to produce an alternating polarity signal at second stage  204 , i.e., an AC signal. Generally, high-frequency switching of the semiconductor switches can produce a higher-quality output signal, but produces increasing amounts of noise and circulating currents. Accordingly, many known switching circuits, such as device-in-parallel or converter-in-parallel alternatives, limit switching frequency (beyond physical limits of the semiconductor devices themselves) to contain noise, and reduce the effects of circulating currents. In embodiments of switching circuit  200  described herein, the provision of decoupling inductor  208  and decoupling capacitor  206  enables greater utilization of high switching frequencies by locally containing the contributing noise and suppressing parasitics or circulating currents to paralleled switching circuit  100 . For example, in at least some embodiments, first semiconductor switch  210  and second semiconductor switch  212  are commutated at a switching frequency of 200 KHz or greater. In alternative embodiments, where acceptable for paralleled switching circuit  100 , first semiconductor switch  210  and second semiconductor switch  212  are commutated at a switching frequency in the range of 1 KHz to 100 KHz. In other embodiments, first semiconductor switch  210  and second semiconductor switch  212  are commutated at a switching frequency in the range of 1 KHz to 10 KHz. 
     In at least some embodiments, paralleled switching circuit  100  includes gate driver circuits  216  and  218  coupled respectively to first and second semiconductor switches  210  and  212  in each phase leg  106 . Gate driver circuits  216  and  218  are controlled independently to synchronize control of first and second semiconductor switches  210  and  212 . Gate driver circuit  216  is coupled to each phase leg  106  and is configured to control first semiconductor switch  210  in each phase leg  106 . Likewise, gate driver circuit  218  is coupled to each phase leg  106  and is configured to control second semiconductor switch  212  in each phase leg  106 . In at least some embodiments, paralleled switching circuit  100  includes DSP  118  (shown in  FIG. 1 ) for controlling gate driver circuits  216  and  218 , and semiconductor switches in phase legs  106 . More specifically, DSP  118  is coupled to respective gate driver circuits for respective semiconductor switches in each switching circuit  200  and is configured to synchronously control the respective gate driver circuits in a complementary manner to convert the first current to the second current, e.g., DC to AC or DC to DC. In controlling gate driver circuits  216  and  218 , and therefore first semiconductor switches  210  and second semiconductor switches  212  in each phase leg  106 , DSP  118  enables substantially equal shares of the total current through paralleled switching circuit  100  to be conducted through each switching circuit  200 . Synchronous control of commutation of the semiconductor switches among each switching circuit  200  includes, for example, simultaneous commutation of first semiconductor switch  210  in each switching circuit  200  by gate driver circuit  216 . Likewise, synchronous control further includes the alternating commutation of first semiconductor switch  210  and second semiconductor switch  212  in each switching circuit  200  such that, in each phase leg  106 , while first semiconductor switch  210  is open, second semiconductor switch  212  is closed, and vice versa. 
     Decoupling inductor  208  is coupled between midpoint node  214  and second stage  204 . Accordingly, decoupling inductor  208  is coupled in series between first semiconductor switch  210  and second stage  204  (and second bus  104 ). Likewise, decoupling inductor  208  is coupled in series between second semiconductor switch  212  and second stage  204 . Decoupling inductor  208  provides a defined di/dt (rate of change in current over time) that prevents abrupt changes in current output to second bus  104 , e.g., an AC bus, during brief periods of time for dynamic transitions, e.g., commutation of first semiconductor switch  210  and second semiconductor switch  212 . Decoupling inductor  208  generally has an inductance value in a range of 1/100 to 1/10 of, or at least one order of magnitude less than, the inductance value of line filter inductor  114 . For example, in certain embodiments, decoupling inductor  208  is an inductor having an inductance in a range of 100 nanohenry to 1 microhenry, i.e., at least one order of magnitude less than line filter inductor  114 . Further, decoupling inductor  208  generally should have good high-frequency characteristics, e.g., rated for operation at frequencies in the range of 100 KHz to 100 MHz. In contrast, line filter inductor  114  generally lacks such high-frequency characteristics, because it is generally rated for operation at or around line frequency (e.g., 50-200 Hertz (Hz)), or around the switching frequency of first and second semiconductor switches  210  and  212  (e.g., 1 KHz to 100 KHz). At high frequencies, e.g., 100 KHz to 100 MHz, line filter inductor  114  functions as an electrical equivalent to a capacitor and would not perform the decoupling functions of decoupling inductor  208 . Accordingly, decoupling inductor  208  reduces high-frequency noise on second bus  104  and reduces circulating currents conducted between phase legs  106 , because current output from each phase leg  106  is decoupled from second bus  104 . 
     Decoupling capacitor  206  is coupled across first bus  102  and provides a defined dv/dt (rate of change in voltage over time) to prevent abrupt changes in voltage on first bus  102 , e.g., a DC bus. Decoupling capacitor  206  generally has a capacitance value in a range of 1/100 to 1/10 of the capacitive value, or one to two orders of magnitude less than the capacitive value of energy storage capacitor  112 . Decoupling capacitor  206 , in certain embodiments, has a capacitance in the range of 1 nanofarad to 100 nanofarad. For example, in one embodiment, decoupling capacitor  206  has a capacitance of 10 nanofarad. Accordingly, decoupling capacitor  206  has a capacitance value that is at least one order of magnitude less than that of energy storage capacitor  112 , depending on the energy storage demands of a given application. Further, decoupling capacitor  206  generally should have good high-frequency characteristics, e.g., rated for operation at frequencies in the range of 100 KHz to 100 MegaHertz (MHz). In contrast, energy storage capacitor  112  generally lacks such high-frequency characteristics, being rated for frequencies in the range around the switching frequency of first and second semiconductor switches  210  and  212 . At high frequencies, e.g., 100 KHz to 100 MHz, energy storage capacitor  112  functions as an electrical equivalent of an inductor and would not perform the decoupling function of decoupling capacitor  206 . 
     The above described embodiments of a switching circuit for a phase leg in, for example, a paralleled switching circuit provide a fully-decoupled phase leg that can be paralleled between a first bus and a second bus, such as between a DC bus and an AC bus or between two DC buses. At least some embodiments of the switching circuit described herein include a decoupling inductor at a second stage to stabilize current output over time, e.g., to filter high-frequency noise at the second stage. At least some embodiments of the switching circuit described herein include a decoupling capacitor at a first stage to stabilize voltage input over time, e.g., to filter high-frequency noise at the first stage. Being fully-decoupled from the first and second buses enables the switching circuit described herein to provide desirable levels of current sharing and reduces parasitics and circulating currents. Accordingly, such switching circuits are not subject to de-rating. At least some embodiments of the switching circuit described herein include an individual gate driver for each switch device, e.g., power semiconductor switch, power MOSFET, insulated gate bipolar transistor (IGBT), bipolar junction transistor (BJT), or other suitable switching device. Control of the switching circuit described herein is, accordingly, simple and cost effective. Embodiments of the switching circuit described herein are efficient and scalable, and contribute little noise to external circuits relative to device-in-parallel or converter-in-parallel alternatives, for example. 
     An exemplary technical effect of the methods, systems, and apparatus described herein includes at least one of: (a) fully-decoupled switching circuits for phase legs in a paralleled switching circuit; (b) improving steady-state and dynamic current sharing among phase legs due to decoupling; (c) reducing complexity and cost of control circuits for respective phase legs due to a common gate drive circuit to control the same position switch device in each phase leg; (d) reducing circulating current among phase legs due to decoupling; (e) avoiding de-rating of paralleled switching circuits or other systems in which switching circuits are embodied due to improved current sharing among phase legs; (f) improving scalability due to utilization of low-cost and readily available discrete components and printed circuit board implementation, and due to reduction in component-count and circuit area as a benefit of avoidance of de-rating; and (g) reducing noise introduced to external circuits on both the source-side and load-side of the switching circuit. 
     Exemplary embodiments of methods, systems, and apparatus for switching circuits are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods may also be used in combination with other non-conventional switching circuits, and are not limited to practice with only the systems and methods as described herein. Rather, the exemplary embodiment can be implemented and utilized in connection with many other applications, equipment, and systems that may benefit from reduced cost, reduced complexity, commercial availability, improved manufacturability, and reduced product time-to-market. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.