Abstract:
A device includes a controller configured to regulate one or more voltages applied to a gate of an insulated gate bipolar transistor (IGBT). The controller is configured to receive one or more voltage values associated with the IGBT, and generate a gating signal and transmit the gating signal to the IGBT. The gating signal is configured to activate or deactivate the IGBT. The controller is configured to generate a voltage clamping signal and transmit the voltage clamping signal to activate or deactivate an active switching device. The active switching device is configured to periodically limit the one or more voltage values associated with the IGBT based at least in part on one or more characteristics of the voltage clamping signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit of priority to International Patent Application No. PCT/CN2012/087758 entitled “Systems and Methods for Control of Power Semiconductor Devices,” filed Dec. 28, 2012, the entirety of which is incorporated by reference herein for all purposes. 
     BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to power electronic devices and, more specifically, to dynamically activating and deactivating a voltage clamping power electronic device. 
     Energy generating devices, such as distributed generators (e.g., photovoltaic panels and wind turbines) rely on semiconductor switching devices (e.g., insulated gate bipolar transistors (IGBTs)) to perform various power conversion operations. To operate an IGBT, a pulsed voltage signal is provided to the gate of the IGBT via a gate driver circuit or controller. Active voltage clamping is often used to protect IGBTs from electrical damage, as IGBTs may be susceptible to high peak voltage while the IGBT is switched off or deactivated. Specifically, if the voltage at the collector of the IGBT exceeds a clamping voltage threshold, the clamping circuitry may be switched on or activated. Unfortunately, because the clamping voltage threshold is typically much lower than the maximum voltage rating of the IGBT, the clamping circuitry may limit the maximum operating voltage range of the IGBT. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Certain embodiments commensurate in scope with the originally claimed invention are summarized below. These embodiments are not intended to limit the scope of the claimed invention, but rather these embodiments are intended only to provide a brief summary of possible forms of the invention. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below. 
     In a one embodiment, a device includes a controller configured to regulate one or more voltages applied to a gate of an insulated gate bipolar transistor (IGBT). The controller is configured to receive one or more voltage values associated with the IGBT, and generate a pulse-width modulation gating signal and transmit the gating signal to the IGBT. The gating signal is configured to activate or deactivate the IGBT. The controller is configured to generate a voltage clamping signal and transmit the voltage clamping signal to activate or deactivate an active switching device. The active switching device is configured to periodically limit the one or more voltage values associated with the IGBT based at least in part on one or more characteristics of the voltage clamping signal. 
     In a second embodiment, a non-transitory computer-readable medium includes code with instructions to receive one or more voltage values associated with an IGBT, and generate a gating signal and transmit the gating signal to the IGBT. The gating signal is configured to activate or deactivate the IGBT. The non-transitory computer-readable medium includes code with instructions to generate a voltage clamping signal and transmit the voltage clamping signal to activate or deactivate an active switching device. The active switching device is configured to periodically limit the one or more voltage values associated with the IGBT based at least in part on one or more characteristics of the voltage clamping signal. 
     In a third embodiment, a device includes an insulated gate bipolar transistor (IGBT) configured to receive a gating signal as an indication to active or deactivate, a zener diode configured to activate at a predetermined clamping voltage threshold value, and an active switching device communicatively coupled to the IGBT and the zener diode. The active switching device is configured to limit one or more voltages associated with the IGBT to the clamping voltage threshold value when activated and to allow the one or more voltages associated with the IGBT to exceed the clamping voltage threshold value when deactivated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention 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 block diagram of a power conversion and control system in accordance with present embodiments; 
         FIG. 2  depicts a schematic diagram of a series of active clamping circuits for insulated gate bipolar transistors (IGBTs), in accordance with an embodiment; 
         FIG. 3  depicts a schematic diagram of an active clamping circuit for an IGBT including gating and clamping circuitry, in accordance with an embodiment; and 
         FIG. 4  depicts a timing diagram of embodiments of gating and clamping control signals, in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     Present embodiments relate to dynamically activating and deactivating voltage clamping circuitry used to protect IGBTs from electrical damage during the period of time the IGBT is switched off. The dynamic voltage clamping circuitry may also allow the voltage of the IGBT to periodically rise above a predetermined clamping voltage threshold. More particularly, the present embodiments allow the IGBT to be operated at its maximum voltage rating to increase power conversion margins by periodically activating and deactivating the clamping circuitry. 
     With the foregoing in mind,  FIG. 1  is a block diagram of a power conversion and control system  10 . The system  10  may include power conductors  12  (e.g., single or poly-phase), a power converter  14 , a controller  16  communicatively coupled via a communications link  18  to the converter  14 , and a load  22  communicatively coupled via a communications link  20  to the converter  14 . In certain embodiments, the system  10  may be used as a starting converter, a continuous duty drive, or similar system for controlling the source of power, and by extension, for example, speed and torque provided to various industrial machinery such as the load  22 . In the case that the system  10  is a starting converter, for example, the system  10  may function as a variable speed alternating current (AC) drive system that drives, for example, a synchronous motor (e.g., load  22 ). 
     In certain embodiments, the converter  14  may include a number of active power electronic switching devices such as silicon-controlled rectifiers (SCRs), thyristors, insulated gate bipolar transistors (IGBTs), and so forth, which may be used to switch to and from “ON” (e.g., activated and/or enabled) and “OFF” (e.g., deactivated and/or disabled) states to control the power flow to the load  22 . For example, in the “OFF” state, the switching devices of converter  14  may restrict the flow of current to only a leakage current. Similarly, in the “ON” state, for example, the switching devices of converter  14  may conduct current when the input voltage exceeds a certain threshold voltage. Specifically, the converter  14  may be any electrical device(s) that transforms direct current (DC) electricity via a DC reactor link to alternating current (AC) electricity, or that transforms alternating current (AC) to electricity direct current (DC) electricity. As will be further appreciated, the converter  14  may include one or more IGBTs and a clamping circuit to clamp, or limit, the peak voltage of each of the IGBTs to a predetermined value during the time each of the IGBTs switches “OFF.” 
     As previously discussed, the system  10  may also include the controller  16 . The controller  16  may control the operation of the converter  14 , and by extension, power flowing to the load  22 . Accordingly, the controller  16  may include a processor that may be used in processing computer instructions, and a memory that may be used to store computer instructions and other data. These instructions may be encoded in programs stored in a tangible non-transitory computer-readable medium such as the memory and/or other storage. In certain embodiments, the controller  16  may control the conversion and/or inversion of AC or DC power received, for example, from one or more distributed generators (e.g., photovoltaic panels, wind turbines, and so forth) by sending switching signals to a number of switching devices, such as IGBTs, SCRs, thyristors, and so forth, that may be included in the converter  14 . In such a case, the controller  18  may control the amount of current flowing from the distributed generators via the power conductors  12  to the load  22 . 
     In one embodiment, the controller  16  may be a pulse width modulation (PWM) controller. Specifically, the controller  16  may include one or more functions of using digital pulse signals (e.g., AC or DC) to produce an output voltage (e.g., AC or DC) level for control of the converter  14 . For example, the controller  16  may transmit an “ON”/“OFF” period PWM signal to the converter  14 , in which the converter  14  may be controlled to switch “ON” when the PWM signal is logically high (i.e., at the rising edge of the PWM signal), and switch “OFF” when the PWM signal is logically low (i.e., at the falling edge of the PWM signal). Thus, the controller  16  may, by extension, control the output (e.g., speed and torque), for example, of the load  22 . It should be appreciated that the converter  14  may include multiple IGBTs, and thus the controller  18  may transmit a separate PWM signal to each of the IGBTs to allow separate control of each of the IGBTs. As will be discussed in further detail below, the controller  16  may also include electrical clamping (i.e., restricting a voltage signal from exceeding a certain defined magnitude or set point) logic and/or firmware to dynamically control the clamping periods along with the PWM “ON”/“OFF” periods transmitted to the converter  14 . 
       FIG. 2  is a schematic diagram of one embodiment of the converter  14  discussed above. The converter  14  may include various active clamping circuitry, which may be configured to dynamically clamp, for example, the upper and lower voltage (e.g., V OUT ) magnitudes of the converter  14 . Specifically, the active clamping circuitry may control the voltage across IGBTs  26  (e.g., S P ) and  30  (e.g., S N ), and thus protect the IGBTs  26  and  30  from substantive electrical (e.g., overvoltage, overcurrent, and so forth) damage. Similarly, active electronic switching devices  28  (e.g., S CP ) and  34  (e.g., S CN ) along with zener diodes  24  and  32  may be configured to control and regulate the voltage of the IGBTs  26  and  30 . For example, the converter  14  may be a DC-DC converter including the IGBTs  26  and  30  each rated to a certain maximum voltage (e.g., 1700V). Continuing, the converter  14  may include the zener diodes  24  and  32  each having a reverse breakdown voltage threshold (e.g., 1000, 1200, 1400V). Accordingly, the zener diodes  24  and  32  may each clamp, or limit, the voltage of the IGBTs  26  and  30  to the reverse breakdown voltage threshold (e.g., 1000, 1200, 1400V), respectively. As will be discussed in greater detail below, in certain embodiments, it may be desirable to operate each of the IGBTs  26  and  30  above the clamping or reverse breakdown voltage threshold (e.g., 1400V) of the zener diodes  24  and  32 . In such a case, a clamping activation and/or deactivation signal (e.g., CLAMP_EN ( 1 ) and/or CLAMP_EN ( 2 )) may be generated, for example, by the controller  16  to dynamically control each of the switching devices  28  and  34 . That is, the controller  16  may control each of the switching devices  28  and  34  to switch “ON” and/or “OFF,” and thus allow each of the IGBTs  26  and  30  to periodically operate at their respective maximum voltage rating (e.g., 1700V). 
     For example, as previously discussed, and as specifically depicted in  FIG. 3 , the active clamping circuitry may be used to protect the IGBT  26  from damage caused by a high peak voltage that may accumulate across the collector of the IGBT  26 . As illustrated, the active clamping circuitry may include the IGBT  26 , gating (e.g., GATING SIGNAL) and clamping (e.g., CLAMP_EN) control signals, gate resistors (e.g., R CLAMP  and R GATE ), the zener diode  24 , the active switching device  28 , and a diode  38 . As noted above with respect to  FIG. 2 , the switching device  28  may be configured to receive the clamping signal (e.g., CLAMP_EN) to turn “ON” and/or “OFF” to allow the IGBT  26 , for example, to periodically operate at its maximum rated voltage (e.g., 1700V). Although referred to as a clamping signal, it should be appreciated that, in certain embodiments, the clamping signal (e.g., CLAMP_EN) may also be a PWM signal. The switching device  28  may be any active electronic device useful to switch, amplify, or convert incoming electrical signals. For example, in one embodiment, the switching device  28  may be an IGBT. Yet, in another embodiment, the switching device  28  may be a bipolar junction transistor (BJT), a metal-oxide-semiconductor field-effect transistor (MOSFET), or other similar active electronic device. In certain embodiments, the switching device  28  may exhibit a faster switching speed than that of the IGBT  26 . Thus, the switching device  28  may be switched “ON” or “OFF” substantially instantaneously to detecting a characteristic (e.g., rising edge, falling edge, change in duty cycle, and so forth) of the clamping signal (e.g., CLAMP_EN). 
     In certain embodiments, the zener diode  24  may be connected in a reversed-bias configuration between the collector of the IGBT  26  and the collector of the switching device  28 . Namely, if the voltage across the collector of the IGBT  26  exceeds the reverse breakdown voltage threshold (e.g., 1400V) of the zener diode  24 , the zener diode  24  may turn “ON” (i.e., conduct current), and thus dissipate current (or power) that may have otherwise flowed into the gate  36  of the IGBT  26 . Specifically, current flowing through the zener diode  24  from the collector of the IGBT  26  to the switching device  28  may increase the voltage on the gate  36  of the IGBT  26 . This may, for example, cause the IGBT  26  to attempt to conduct a higher current than the maximum current rating of the IGBT  26 . More particularly, when the IGBT  26  switches “OFF” (e.g., when the gating signal (GATING SIGNAL) is logically low), the voltage of the collector of the IGBT  26  may rise due to a parasitic inductance (e.g., L PP ) that may occur across the collector of the IGBT  26 . Accordingly, the active clamping circuitry may effectively clamp the peak collector voltage to approximately the reverse breakdown voltage threshold (e.g., 1400V) of the zener diode  24 . 
     As previously discussed, in certain embodiments, it may be desirable to operate the IGBT  26  above the clamping or reverse breakdown voltage threshold (e.g., 1400V) of the zener diode  24 . For example, for an IGBT  26  having a maximum voltage rating of 1700V, it may be advantageous to drive the IGBT  26  to operate at the 1700V voltage rating to increase the power conversion margins. That is, instead of the voltage being clamped at the threshold voltage (e.g., 1400V) of the zener diode  24 , the IGBT  26  may be allowed to operate at its maximum voltage rating in so long as that maximum voltage (e.g., 1700V) is not exceeded. In such a case, a clamping enable and/or disable signal (e.g., CLAMP_EN) may be generated by the controller  16  to control the switching device  28  and zener diode  24  (e.g., clamping circuitry) to turn “ON” and/or “OFF,” and thus allow the IGBT  26  to periodically operate at the maximum voltage rating (e.g., 1700V). 
     Turning now to  FIG. 4 , the techniques as discussed above may be better understood with respect to a gating signal  42  (GATING SIGNAL) and a voltage clamping signal  44  (CLAMP_EN). As also noted above, the signals  42  (GATING SIGNAL) and  44  (CLAMP_EN) may be PWM signals generated by the controller  16 , which may include a processor that may execute instructions for carrying out presently disclosed methods. These instructions may be encoded in programs stored in a tangible non-transitory computer-readable medium such as a memory and/or other storage of the controller  16 . In certain embodiments, the controller  16  may be referred to as a gate driver, since the controller  16  may transmit the gating signal  42  (GATING SIGNAL) to the IGBT  26 . In particular, the IGBT  26  may be controlled to switch “ON” when the gating signal  42  (GATING SIGNAL) is logically high, and switch “OFF” when the gating signal is logically low. Similarly, the clamping signal  44  (CLAMP_EN) may be generated by the controller  16  to control the switching device  28  and zener diode  24  to dynamically switch “ON” and/or “OFF.” Accordingly, the controller  16  may control when the voltage of the IGBT  26  is to be clamped, as opposed to allowing the zener diode  24  to clamp the voltage of the IGBT  26  in every instance the clamping voltage threshold is exceeded. 
     As depicted in  FIG. 4 , the clamping signal  44  (CLAMP_EN) may become logically high at substantially the same point in time that the gating signal  42  (GATING SIGNAL) is logically high. In other embodiments, the clamping signal  44  (CLAMP_EN) may become logically high after period of time following the gating signal  42  (GATING SIGNAL) becoming logically high. That is, the clamping signal  44  (CLAMP_EN) may become logically high at a point in time  47  just before, or just after the gating signal  42  (GATING SIGNAL) becomes logically high. Thus, over the duty cycle (i.e., the percentage of time the gating signal  42  and the clamping signal  44  are each logically high during a pulse period) of the gating signal  42  (GATING SIGNAL), the voltage of the IGBT  26  is clamped to the clamping voltage threshold of the zener diode  24 . However, as previously discussed, the voltage across the collector of the IGBT  26  may rise during “switch OFF,” or the period in which the gating signal  42  (GATING SIGNAL) is logically low. Accordingly, a delay may be introduced between the time the gating signal  42  (GATING SIGNAL) becomes logically low (at the falling edge  46 ) and the time the clamping signal  44  (CLAMP_EN) becomes logically low (e.g., at the falling edge  48 ). As such, during the delay period (i.e., substantially the time it takes the IGBT  26  to completely switch “OFF”) between signals  42  and  44  becoming logically low, the voltage of the IGBT  26  may be clamped to the clamping voltage threshold of the zener diode  24 , and thus protected from potential damage or failure due to overvoltage and/or overcurrent heating. In one embodiment, the delay period may be approximately 1-10 microseconds. 
     As previously noted, in certain embodiments, statically clamping the peak voltage of the IGBT  26  may present an undesirable effect. Namely, as long as the peak voltage is above the clamping voltage threshold, the zener diode  24  (e.g., clamping circuitry) will be “ON,” even though the IGBT  26  may be periodically switched “OFF.” Since the clamping voltage threshold (e.g., 1400V) may be, in many instances, lower than the maximum voltage rating of the IGBT  26 , the switching device  28  and zener diode  24  may actually limit the peak voltage of the IGBT  26  to a margin much lower than the maximum voltage rating of the IGBT  26 . Accordingly, the clamping signal  44  (e.g., CLAMP_EN) generated by the controller  16  and transmitted to the switching device  28  may be pulsed or modulated, such that the voltage across the IGBT  26  can rise above the clamping voltage threshold of the zener diode  24  when the IGBT  26  is periodically switched “OFF.” For example, should the maximum voltage rating of the IGBT  26  be approximately 1700V and the clamping voltage threshold be approximately 1400V, during the period the clamping signal  44  (e.g., CLAMP_EN) is logically low, and by extension, the switching device  28  switches “OFF,” the IGBT  26  may be operated more closely to its maximum voltage rating of 1700V. Thus, as long as the voltage across the collector of the IGBT  26  does not exceed its maximum voltage rating (e.g., 1700V), the IGBT  26  may be operated at the maximum voltage rating to increase the power conversion and operating margins of the IGBT  26 . 
     Technical effects of present embodiments relate to active and dynamic voltage clamping to protect IGBTs from electrical damage. Particularly, an active switching device is provided to clamp the voltage of the IGBT during the period of time the IGBT is switched off. However, the active switching device may also allow the voltage of the IGBT to periodically rise above the clamping voltage threshold. More particularly, the present embodiments allow the IGBT to be operated at its maximum voltage rating to increase power conversion margins by periodically deactivating the clamping circuitry. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention 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.