Abstract:
A control method and arrangement that monitors the condition and operating parameters of a power electronic system having power electronic devices and responds to various detected abnormalities to optimize operation of the power electronic system. The arrangement increases reliability of operation and optimizes the continuous supply of power to a load. The arrangement also includes the capability for diagnosing the parameters of the power electronic switches including drive current, drive voltage and operating temperature and for communicating the status information in a coordinated fashion.

Description:
[0001]    This application is a continuation-in-part application of application No. 10/192,441 filed on Jul. 11, 2002 in the names of Mikosz et al. (which in turn is a divisional application of application Ser. No. 09/556,259 filed on Apr. 24, 2000 based on Provisional application No. 60/131,724 filed on Apr. 30, 1999) and claims the benefit of U.S. Provisional Application No. 60/375,799 filed on Apr. 26, 2002 and 60/369,202 filed on Apr. 1, 2002. MONITORING AND CONTROL FOR POWER ELECTRONIC SYSTEM 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to the field of power electronic systems and more particularly to control methods and arrangements that monitor the condition and operating parameters of the power electronic system and power electronic switches and provide appropriate action to optimize operation thereof.  
           [0004]    2. Description of Related Art  
           [0005]    Various power electronic systems are known for supplying power, regulating power, and transferring power from one source to another in order to provide continuous power to a load. Ascertaining the proper operation of the various components of these systems is important in order to most appropriately decide how to best assure the continuous supply of power to the load. While these arrangements may be useful and generally satisfactory for their intended purposes, they do not provide appropriate diagnostics or system control with sufficient emphasis on the priority of the continuous supply of the connected load.  
         SUMMARY OF THE INVENTION  
         [0006]    Accordingly it is a principal object of the present invention to provide a control method and arrangement that monitors the condition and operating parameters of a power electronic system having power electronic devices and responds to various detected abnormalities to optimize operation of the power electronic system.  
           [0007]    It is another object of the present invention to provide a diagnostic arrangement for a power electronics system including power electronic switches that monitors the parameters of power electronics switches including drive current and voltage at a control connection of the series-connected switches in a stack of stages that make up a power electronic switch.  
           [0008]    These and other objects of the present invention are efficiently achieved by a control method and arrangement that monitors the condition and operating parameters of a power electronic system having power electronic devices and responds to various detected abnormalities to optimize operation of the power electronic system. The arrangement increases reliability of operation and optimizes the continuous supply of power to a load. The arrangement also includes the capability for diagnosing the parameters of the power electronic switches including drive current, drive voltage and operating temperature and for communicating the status information in a coordinated fashion. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]    The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in conjunction with the accompanying drawing in which:  
         [0010]    [0010]FIG. 1 is a block diagram representation of a power electronic system utilizing the control arrangement of the present invention;  
         [0011]    FIGS.  2 - 8  are diagrammatic representations of signals at various points in the system of FIG. 1;  
         [0012]    [0012]FIG. 9 is a one-line, block diagram representation of a power electronics switching system utilizing the control arrangement of the present invention;  
         [0013]    [0013]FIG. 10 is a one-line, diagrammatic representation of portions of a solid-state switch of FIG. 9;  
         [0014]    [0014]FIG. 11 is a block and schematic diagram of portions of a switch control/monitor stage and a switch stage of FIG. 1; and  
         [0015]    [0015]FIG. 12 is a block and schematic diagram of portions of a switch control/monitor stage and a switch stage of FIG. 1 illustrating additional features.  
     
    
     DETAILED DESCRIPTION  
       [0016]    Referring now to FIG. 1, the control arrangement and method of the present invention will be described in connection with an illustrative system  15  that includes a controller  18  that monitors the condition and operating parameters of various components of the system  15  and takes appropriate action to optimize operation thereof, e.g. the operating characteristics of an illustrative electronic switch stage  10  are monitored as will be explained in more detail hereafter. As illustrated, the electronic switch stage  10  includes a main path between lines  12  and  14  that is controlled between on and off states, corresponding to respective conductive and nonconductive states, via a control connection at  16 . In a specific illustrative example, the electronic switch stage  10  is a thyristor, IGBT, TRIAC, pair of inverse-parallel connected SCR&#39;s, or other actively controlled device.  
         [0017]    The system  15  includes an illustrative communications arrangement  22  that cooperates with the controller  18  to provide information to the controller  18  over communications lines at  20 , which in specific embodiments is formed by one or more data buses and/or control lines. In the illustrative embodiment, the communications arrangement  22  includes a switch control/monitor stage  30  that is located in the vicinity of the system component to be monitored, e.g. the electronic switch stage  10 , and that transmits monitored information to a communications encoder/multiplexer stage  26 , “comm. encoder/mux”  26  hereafter, via a communications link  28 , e.g. a dielectric medium such as fiber optics in a specific embodiment. As illustrated, where multiple components are monitored by the system  15 , multiple switch control/monitor stages  30  are provided along with multiple communication links  28 , e.g.  28   a ,  28   b . The comm. encoder/mux stage  26  then functions to multiplex the information on the various communication links  28  and provides the information in a predetermined multiplexed format at  20  to the controller  18 .  
         [0018]    The control connection  16  of the electronic switch stage  10  is connected to a gate drive signal at  24  provided by the switch control/monitor stage  30 . In this illustrative example, the system  15  monitors the gate drive signal at  24  and/or the temperature of the switch stage  10  via data at  32 . This arrangement is especially useful where the illustrative electronic switch stage  10  or various other component is located remotely from the controller  18  and/or where the illustrative electronic switch stage  10  is located in a more severe environment that is deleterious for the controller  18 , e.g. high-noise, medium voltage, high-temperature etc. In one specific embodiment, the temperature of the switch stage  10  is measured at the location of the switch control/monitor stage  30  with the switch control/monitor stage  30  being in the proximate vicinity of the switch stage  10 , e.g. on a common mounting arrangement or heat sink  34  (not shown in detail).  
         [0019]    Considering now an illustrative embodiment of the communications arrangement  22  of the system  15  and referring now additionally to FIG. 2, the information on the communication link  28  includes a representation of the gate drive signal  24 , such that a pulse signal  40  is sent over the communications link  28  when the electronic switch stage  10  is conducting. The pulse signal  40  is sent on a repetitive basis, e.g. each basic clock cycle or each half cycle of a fundamental waveform that is present on the line  12  to the electronic switch stage  10 . The receipt of this signal  40  by the comm. encoder/mux stage  26  and the transmission of this representation to the controller  18  over lines  20  also indicates that the communications arrangement  22  is operational and that the electronic switch stage  10  is not shorted.  
         [0020]    In the illustrative embodiment of FIG. 1, the electronic switch stage  10  is one stage of an overall series-connected electronic switch, e.g. six stages as depicted in FIG. 1 by a second stage  10   a  and a sixth stage  10   b . Also provided for each stage is one of the switch control/monitor stages  30 , e.g.  30 ,  30   a ,  30   b  which transmits a signal on each of the communication links  28 , e.g.  28 ,  28   a  and  28   b , to the comm. encoder/mux stage  26 . For example, as depicted in FIG. 2, respective signals  42  and  44  are transmitted for the second and sixth electronic switch stages  10   a  and  10   b  which are generated simultaneously and repetitively. The comm. encoder/mux stage  26  then multiplexes the received pulse signals, e.g.  40 ,  42  and  44 , and provides the multiplexed signal at lines  20  to the controller  18 . Accordingly, the receipt by the controller  18  of the continuous train of pulses verifies that each switch stage of the stages  10 ,  10   a ,  10   b  etc., denoted as  10   x  hereafter, is conducting. If the pulses are not continuous, e.g. not present in the predetermined pattern and spacing as shown in FIG. 3, i.e. one or more of the pulses are missing at the periodic rate, then the controller  18  is advised/alerted that something is wrong with either one of the electronic switch stages  10   x  or the communication arrangement  22 . If the pulse train of multiplexed signals at  20  is synchronized to the controller  18 , the controller  18  can identify which of the stages has a malfunction, e.g. stage  3  in FIG. 3 as indicated by the missing pulse denoted  62 .  
         [0021]    Considering now an illustrative embodiment where additional information is transmitted over the communications arrangement  22  and referring now additionally to FIG. 4, it is desirable for the controller  18  to ascertain additional information about the various components of the system  15 , e.g. the temperature of the electronic switch via the sensed temperature signal  32 . To accomplish the communication of additional information, the switch control/monitor stage  30  encodes additional information along with the gate driver signal information, e.g. as shown in FIG. 4 by the addition of a pulse signal  50  that represents temperature of the electronic switch stage  10  along with a representation of the gate driver signal, e.g. pulse signal  52 . In a specific arrangement, the width of the pulse  50  is proportional to the sensed temperature at  32 . Thus, the pulse signals  50 ,  52  are sent over the communications link  28  on a periodic basis, e.g. as discussed before, for each basic operational cycle of the system  15 . For example, pulse signals  50 ,  52  correspond to a switch control/monitor stage  30  associated with a first electronic switch stage  10  and pulse signals  54 ,  56  correspond to the stage  30   a  associated with a second electronic switch stage  10   a . It should be noted that in FIG. 4, while the pulses are shown sequentially for each stage, the pulses for each of the stages is sent repetitively and simultaneously, the representation in FIG. 4 being the multiplexed sequential arrangement performed by the comm. encoder/mux stage  26  in response to the continuous information received from the various stages on the communication links  28 ,  28   a ,  28   b  etc.  
         [0022]    In a specific embodiment, the comm. encoder/mux stage  26  also incorporates an ambient temperature signal to the controller  18 . For example, with additional reference to FIG. 5, after the comm. encoder/mux stage  26  outputs a sequence of pulses corresponding to each of the stages, an ambient temperature signal  60  is encoded or multiplexed into the pulse train in place of the first stage signal or other position. Thus, the controller  18  receives a pulse train of signals representing the gate signal and the temperature of each of the switch stages  10   x  followed by the ambient temperature of the environment of the controller  18  and the comm. encoder/mux stage  26 . In this manner, the temperature rise of each switch stage  10  above the ambient temperature is available. Additionally, as shown in FIG. 5, the absence of a pulse signal for any of the stages, e.g. at  63  for stage  3 , indicates a malfunction of the communications link or the gate drive signals or the shorted condition of the respective switch stage  10  etc.  
         [0023]    In accordance with additional aspects of the present invention, and referring now additionally to FIG. 6, in a preferred embodiment, the gate driver signal pulse  40  is transmitted over the communications link  28 , on a normal basis in one specific embodiment, or in another specific embodiment, upon a requested basis as determined by the controller  18 . For example, the controller  18  issues a request signal, as illustrated at  64  in FIG. 6, on a communications line  29 , e.g. a dielectric medium such as fiber optics in a specific embodiment, to instruct/condition the switch control/monitor stage  30  to initiate the transmission of the combined additional information of the gate signal and the temperature of the switch stage  10 . Thus, the stage  30  sends the normal signals as shown in FIG. 2 until a request signal is received whereupon the signals depicted in FIG. 4 are sent, all as depicted in the sequence of FIG. 6.  
         [0024]    In accordance with additional aspects of the present invention, the controller  18  over the communication lines at  20  is arranged to issue predetermined ON or OFF signals to control the conductive state of the switch stages  10  to  10   b  over the communications link  29  of the communications arrangement  22 . In response to the ON or OFF signals at  20 , the switch control/monitor stage  30  sends a gate drive control signal at  24  to turn the switch on or off in accordance with the received signal. For example, signals at  20 , either on one line or as a coded representation, are responded to by the comm. encoder/mux stage  26  which issues an ON signal representation over the communications link  29  to the switch control/monitor stage  30 . The switch control/monitor stage  30  decodes the ON signal representation on the communications link  29  and outputs a signal at  24  to the switch stage  10 . In one embodiment, a momentary ON signal at  20  causes the stage  30  to turn the switch stage  10  on and the switch stage  10  is turned off only upon the issuance of a momentary OFF signal at  20 . In another embodiment, the ON signal is continuously output at  29  until the switch control/monitor stage  30  responds with one or more predetermined signals over the communication link  28  to acknowledge that the ON signal has been received and acted upon and/or that the switch stage  10  is conducting, e.g. as shown at  65  or  66  in FIG. 5.  
         [0025]    In a specific embodiment, the ON/OFF signals at  20  are encoded over the communications link  29  as a pulse train of a predetermined number of pulses, the ON and OFF signals being a different number of pulses. The comm. encoder/mux stage  26  encodes the pulse train and the switch control/monitor stage  30  counts the pulses of the signal and determines whether or not the received signal is an ON or OFF signal. In one embodiment, the request for diagnostic signal issued by the comm. encoder/mux stage  26  at  29  is a third signal, e.g. a different number of pulses than the ON or OFF signal representations In another embodiment, the request for diagnostic signal to start the transmission of temperature signals over the communication link  28  is the transmission of a predetermined “ON” signal over the link  29 . Considering another illustrative embodiment of the present invention and referring now additionally to FIG. 7, the temperature signal alone is communicated via the communications arrangement  22  of FIG. 1, e.g. signal  50  for stage  10 ,  54  for stage  10   a , and the signal  60  for ambient temperature at the stage  26 . In another embodiment, a distinct ready signal is utilized by the comm. encoder/mux stage  26  to ready the switch stages  10   x  for operation in response to an ON command being received from the controller  18  when the switch stages  10   x  are non-conducting. In such cases, the switch control/monitor stages  30  respond to the detection of the distinct ready signal, e.g. predetermined number of pulses at  29 , by sending a signal such as  40  in FIG. or  65  or  66  of FIG. 5 over the communications link  28 . When the signals are received by the comm. encoder/mux stage  26 , it can be determined that the switch stages  10   x  are ready for operation and ON signals can be issued over the communication links  29 .  
         [0026]    The system  15  in a preferred embodiment is applied to a multi-phase electrical power distribution system operating at medium voltages. Accordingly, as shown in FIG. 1, the system  15  includes additional comm. encoder/mux stages  26 , e.g.  26 - 2  and  26 - 3  for respective second and third phases of an electrical power source. In one embodiment, the stages  26 ,  26 - 2  and  26 - 3  are connected to receive signals from the controller  18  over a common data bus  20  while in other embodiments the signaling paths are independent. In such systems, when the power electronic switch of stages  10 , 10   a , 10   b  etc. is non-conducting, it may be desirable to verify its readiness for operation, especially when it may be called upon for rapid, high-speed operation in a high-speed source-transfer application. In one embodiment, and referring now to FIG. 8, when the comm. encoder/mux stage  26  receives a signal at  20  from the controller  18  representing that the switch stages  10   x  are to be tested, the comm. encoder/mux stage  26  issues ON commands to a first portion of the switch control/monitor stages  30 , e.g. N/2 where there are N total switch stages  10   x , or (N+1)/ 2  where N is an odd number, and thereafter issue ON commands to the remaining switch control/monitor stages  30 . Accordingly, the information representing operation of the various switch stages  10   x  is provided to the controller  18  as shown in FIG. 8, first for the first three stages then for the next three stages. This is useful because a non-conducting switch can be tested while the overall switch remains non-conducting. Additionally, in a preferred embodiment, the ambient temperature is also provided, as shown at  60  in FIG. 8. As before, in various embodiments, this can be done with the temperature representations for each stage as shown in FIG. 8 or without the individual temperature representation signals.  
         [0027]    Referring now to FIG. 9, a power electronic switching system functioning as a high-speed source transfer switching system (HSSTSS)  110  is illustrative of a specific system application for which the control arrangement and method of the present invention of FIGS.  1 - 8  is useful. The HSSTSS  110  supplies a load at  114  with an alternating-current waveform via either a first AC source at  116  or a second AC source at  118 . The first and second AC sources  116  and  118  and the load at  114  as provided in an electrical power distribution system are typically multi-phase circuits which are represented in FIG. 9 by a one-line diagram. The HSSTSS  110  includes a first solid-state switch, SSS 1 ,  120  and a second solid-state switch, SSS 2 ,  122 , which can also be characterized as electronic switches or power electronic switches. The HSSTSS  110  via a system control  112  controls either SSS 1  to supply the load at  114  via the first source  116  or controls SSS 2  to supply the load at  114  via the second source  118 . In a specific embodiment, the system control  112  includes the controller  18  of FIG. 1. The system control  112  provides appropriate control signals at  128 ,  130  to control the operation of each respective solid-state switch, SSS 1   120  and SSS 2   122 . In the specific illustrative embodiment, the system of FIG. 9 utilizes the communications arrangement  22  of FIG. 1. Accordingly, the control signals at  128 ,  130  are utilized by the communications arrangements  22 - 1  and  22 - 2  to control the respective solid-state switches SSS 1   120  and SSS 2   122  over respective gate drive signal arrangements  241  and  24 - 2 .  
         [0028]    In operation, the system control  112  samples the voltage waveforms of each source  116 , 118 , e.g. via respective sensing inputs at  124 , 126  to detect when transfer between the sources is desirable, e.g. sensing outages and momentary interruptions as well as voltage sags and swells based on the source supplying the load being above or below preset levels. For example, assume that SSS 1   120  is turned on by the system control  112  via signals at  128  so as to be conductive and supply the load at  114 . If the system control  112  via the sensing input  124  senses that the voltage of the first source at  116  is exhibiting undesirable characteristics, the system control  112  via the control signals at  128 ,  130  turns off SSS 1  and turns on SSS 2  so as to transfer the supply of the load at  114  from the first source at  116  to the second source at  118 . As used herein, the term “incoming” is used to describe the source and the SSS that will be turned on to supply the load (e.g. the second source at  118  and SSS 2  in the illustrative example), and the term “outgoing” is used to describe the source and the SSS that is being turned off (e.g. the first source at  116  and SSS 1  in the illustrative example).  
         [0029]    Referring now to FIG. 10, each of the solid-state switches SSS 1  and SSS 2  includes one or more arrays of inverse parallel connected thyristors, e.g.  140   a  and  140   b  for SSS 1  and  142   a  and  142   b  for SSS 2 . In illustrative implementations, each array of thyristors is rated in the range of 2-12 kv. To provide operation in medium voltage systems, e.g. operating in the range of 2-34.5 kv, one or more of such thyristors SSS 1  and SSS 2  are connected in series for each phase of the sources, e.g. a plurality of such thyristors being referred to as a stack. Thus, while the term thyristor is used for the solid-state switches SSS 1 ,  140  and SSS 2 ,  142 , in specific implementations at medium voltages, this commonly refers to a thyristor stack. For example, in a specific embodiment, each of the solid-state switches SSS 1  and SSS 2  is implemented by a plurality of the switch stages  10   x  of FIG. 1.  
         [0030]    Considering now operation of the control arrangement and method of the present invention, transfer of the load at  114  from one source to the other, e.g. the first source at  116  to the second source at  118 , is generally accomplished by removing the gating signals at  128   a ,  128   b  to shut off SSS 1  and starting the gating signals at  130   a ,  130   b  to turn on SSS 2 . Thus, the first source at  116  ceases to supply the load at  114  and the second source at  118  begins to supply the load at  114 . For desirable transfer control, the controller  112  is provided with additional sensing inputs, e.g. the incoming source-voltage differential is determined by the load voltage at  114  as sensed via a sensing input  127  or by the differential of the source voltages sensed at  124 ,  126 , and the current to SSS 1  and SSS 2  being sensed via respective current sensing inputs at  129  and  131 .  
         [0031]    In accordance with additional aspects of the present invention, the system control  112  is provided with features to respond to an overheated condition of the solid state switches SSS 1  and SSS 2  to transfer the load at  114  to the alternate source. For example, if the temperature sensed via either the communications arrangement  22 , or a separate temperature sense line  150  in a specific embodiment, indicates an overheated condition, the system control  112  proceeds with a high-speed transfer. The system control  112  then denotes the alternate source as the preferred source. The now denoted alternate source with the overheated switch is still available on a temporary basis for transfers when the system control  112  detects voltage disturbances on the source currently feeding the load such that transfer is required. In an illustrative embodiment, the overheated condition is defined by any stage of a solid-state switch SSS having a sensed temperature that exceeds the ambient temperature by a predetermined differential. i.e. temperature rise. For example, with reference to FIG. 1, if any electronic switch stage  10  has a sensed temperature at  32  that exceeds the predetermined limits, an overheated condition is determined.  
         [0032]    When an overheated condition is detected, if it is not possible to transfer to another viable source, the system  110  includes additional features to initiate and accomplish a backup transfer to bypass and isolate the switches SSS 1  and SSS 2  of the system  110 . Specifically, in an illustrative embodiment, as shown in FIG. 9, to accomplish a bypass/isolation sequence, the system controller  112  controls two bypass switches BP- 1  and BP- 2  and two isolation switches I- 1  and I- 2 . The switches BP- 1 , BP- 2 , I- 1  and I- 2  are controlled via respective control lines  160 ,  162 ,  164  and  166 . In accordance with additional features of the present invention, the bypass/isolation sequence is performed to assure optimum load continuity, e.g. as described by the following steps:  
         [0033]    Disable high speed transfer control (maintain SSS 1 , SSS 2  states);  
         [0034]    Close bypass switch(es) (e.g. BP- 1 ) to match the presently conducting SSS(&#39;s), e.g. SSS 1 ;  
         [0035]    Confirm that the appropriate bypass switches respond;  
         [0036]    Open all isolation switches (e.g. I- 1 , I- 2 );  
         [0037]    Confirm that the appropriate isolation switches respond;  
         [0038]    Remove all gating signals (e.g. at  128 , 130 ) from all SSS&#39;s  
         [0039]    Enable backup transfer control (e.g. in this case because an SSS is deemed unusable) In situations where backup transfer control is enabled, e.g. to perform maintenance or service, an overheated SSS, or otherwise unusable SSS (e.g. due to lack of control), the system control  112  is capable of providing source transfer control using the bypass switches BP- 1 , BP- 2 , with the isolation switches I- 1 , I- 2  remaining open.  
         [0040]    In accordance with additional features of the present invention, when diagnostic information is received by the system controller  112  indicating a potential shorted condition of a switch SSS, e.g. as detected by the loss of the gating signal  40  or  52  for a particular switch stage  10   x  in FIGS.  1 - 8 , the system controller  112  will identify the switch SSS and the location of the stage within the switch of the potential problem. Appropriate flags, alarms etc. are set and issued. However, the system  110  will continue to operate normally and be fully functional since the switches SSS are designed with devices having suitable predetermined ratings sufficient to be able to function when one of the switch stages  10   x  is shorted. If diagnostic information is received that identifies a potential shorted condition of a second of the switch stages  10   x  within the same phase or pole of a switch SSS, the system controller  112  initiates the backup transfer mode as discussed hereinbefore and the high-speed transfer function is disabled. As discussed hereinbefore in connection with diagnostics of the operating parameters of the switches such as SSS 1  of the system  110  and the switch stages  10   x  of FIG. 1, the loss of the signals  40  or  52  indicates that either the switch stage  10   x  is shorted, the communications arrangement  22  is not functioning or the gate drive signals at  24  are not functioning.  
         [0041]    Considering yet further additional features of the present invention, the system controller  112  also monitors the voltage across each switch SSS that is supposed to be in a conducting mode, i.e. the switch SSS that is supplying the load at  114 . For example, the system controller  112  monitors the differential voltage between  116  and  114  for switch SSS 1 . If the differential voltage is greater than a predetermined value, e.g. 1500v for a 15 kV system, the system controller  112  concludes that the there is a malfunction. This detected condition could be caused by an isolation switch being open (which would not be normal), a blown fuse in the circuit, or the discontinuity of the switch SSS 1  (i.e. non-conducting status such as caused by an open circuit or broken connection). If this condition is detected and persists for a predetermined time interval, e.g. 2 milliseconds, the system controller  112  initiates a transfer to the second source  118  by turning on the switch SSS 2 , and also locks out any transfer back to the switch SSS 1 . Of course, if for any reason an alternate viable source is not available, the system controller initiates a backup transfer as discussed hereinbefore. In addition or as an alternative to the diagnostic testing of non-conducting switches as discussed hereinbefore, if a switch SSS 1  has not been turned on in a predetermined period of time, e.g. one day, the system controller  112  initiates a transfer to interrogate the switch SSS 1  to verify proper operation to ensure that a viable alternate source is available if needed.  
         [0042]    With additional reference now to FIG. 11 and in accordance with other aspects of a specific embodiment of the present invention, a representation of the voltage at the gate  33  of a switch device  35  of the switch stage  10  is also monitored and communicated from the switch control/monitor stage  30  to the comm. encoder/mux stage  26  over the communications link  28 . Thus, information representative of the gate voltage at  33  (i.e. V G , the voltage between the gate  33  and the cathode of the switch device  35 ) provides useful information about the status of the switch stage  10  in addition to the gate drive signal at  24  connected to the gate driver stage  31  that actually provides drive signal to the gate drive circuitry  31  that drives the gate  33  of the switch device  35 . For example, the gate drive signal at  24  provides information about the status of the switch control/monitor stage  30  and the gate drive circuitry  31 , this gate drive signal  24  corresponding to the drive current into the gate drive circuitry  31  of the switch stage  10  if the gate drive signal  24  is not directly connected to the gate  33  via a resistance or the like (and corresponding to the gate drive current into the gate  33  of the switch device  35  if the gate drive signal  24  is directly connected to the gate  33  via a resistance or the like). In addition, the gate voltage V G  at the gate  33  provides status information about the switch device  35  so as to detect a shorted gate, a miswired switch device, reversed gate leads or shorted wiring or circuitry. The gate voltage V G  at  33  being at least equal to a threshold value (e.g. 0.5 volts) signifies that the switch device  35  is operating properly while a lower voltage indicates a shorted gate or other problem. The representation of the voltage V G  at the gate  33  can be sent in various ways according to various specific embodiment, e.g. in addition to or in lieu of the temperature signal  50 . In one specific embodiment, a status signal is sent as the gate drive signal  40  that is the result of the logical AND function of a representation of the gate drive signal at  24  and the voltage V G  at the gate  33  of the switch device  35 , e.g. as shown diagrammatically in FIG. 11 by the AND gate  37  providing an output at  39  representative of this combined signal. Thus, this signal at  39  is a high logic level if both the gate drive signal  24  and the voltage V G  at the gate  33  each satisfy the required levels representing appropriate operation. As discussed hereinbefore, the signal representing the voltage V G  can be sent on a normal status basis or as requested by the controller  18 . With additional reference to FIG. 12, an arrangement is illustrated that utilizes an actual representation of the gate drive current into the gate  33 , e.g. as shown diagrammatically by an operational amplifier stage  36  providing a differencing function between the gate drive signal at  24  and the voltage V G  at the gate  33 , the operational amplifier stage  36  providing this gate current representation at an output  38  that is connected to one input of the AND gate  37 . Thus, the output  39  of the AND gate  37  in FIG. 12 represents the presence of both gate drive current and gate voltage. A buffer amplifier  41  is shown between the gate voltage signal at  33  and the input of the AND gate  37  for the situation where the AND gate  37  does not accept the unbuffered levels of the signal at  33 .  
         [0043]    While there have been illustrated and described various embodiments of the present invention, it will be apparent that various changes and modifications will occur to those skilled in the art. Accordingly, it is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the present invention.