Abstract:
Motor drive apparatus and methods are presented in which a standby controller uses at least one switching device to power an inverter in a normal mode and to remove power from the inverter and other motor drive components during a standby mode for improved energy efficiency.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to motor drives and more particularly to techniques and apparatus for energy efficient AC motor drive standby operation. Motor drives operate AC electrical motors using power from an AC or DC input source. In many industrial operations utilizing electric motor drives, it is useful to stop the driven motor while maintaining the drive in a standby mode for subsequent resumption of motor operation. Moreover, in controlled industrial operations, the switching between normal and standby modes may be automated, with suitable commands for entering and exiting the standby mode being generated by industrial control components interconnected with the motor drive. However, it is important to conserve energy in operation of such automated systems, and conventional standby mode operation of motor drives consumes excessive amounts of power. Thus, there remains a need for improved motor drive apparatus and techniques by which power consumption during standby operation can be reduced. 
       SUMMARY 
       [0002]    Various aspects of the present disclosure are now summarized to facilitate a basic understanding of the disclosure, wherein this summary is not an extensive overview of the disclosure, and is intended neither to identify certain elements of the disclosure, nor to delineate the scope thereof. Rather, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the detailed description that is presented hereinafter. 
         [0003]    The present disclosure involves the motor drive apparatus operable in a normal mode and a standby mode. The apparatus includes a motor drive input as well is an inverter to drive a motor load. In certain embodiments, the motor drive may further include a rectifier receiving power from the drive input and providing DC output power to the input of the inverter. In other embodiments, the motor drive receives DC input power which is provided to the input of the inverter. One or more switching devices are provided between the inverter input and the drive input, and a standby controller operates the switching device to selectively allow input power to flow to the inverter in normal operation of the drive and to prevent power from flowing from the drive input to the inverter in a standby mode. 
         [0004]    Unlike conventional standby mode operation in which the inverter and any included rectifier remained powered during standby mode, the present disclosure provides further energy conservation by preventing application of power to the inverter, and other nonessential system components may be also powered down for further energy savings during standby mode. In certain illustrated embodiments, the switching device is a main circuit breaker employed in a pre-charging apparatus which can also be used in initial startup of the motor drive for pre-charging a DC bus, whereby no new or additional hardware needs to be added to the motor drive to implement the standby mode power saving concepts of the present disclosure. In certain embodiments, moreover, a pre-charge power supply is connected to the input power upstream of the switching device to maintain power to at least one control component of the motor drive during the standby mode operation, thereby facilitating quick return to normal mode operation. 
         [0005]    In accordance with further aspects of the disclosure, methods and computer readable mediums having computer executable instructions are provided for motor drive operation, in which electrical power is provided to one or both of the motor drive rectifier and inverter, and a standby mode command is received. In response to receipt of the standby command, operation of at least one switching device is changed to discontinue provision of electrical power to the rectifier and/or inverter. In certain embodiments, a command is received to exit the standby mode, in response to which the operating mode of the switching device is changed to resume provision of electrical power to the rectifier and/or inverter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The following description and drawings set forth certain illustrative implementations of the disclosure in detail, which are indicative of several exemplary ways in which the various principles of the disclosure may be carried out. The illustrated examples, however, are not exhaustive of the many possible embodiments of the disclosure. Other objects, advantages and novel features of the disclosure will be set forth in the following detailed description when considered in conjunction with the drawings, in which: 
           [0007]      FIG. 1  is a simplified schematic diagram illustrating an exemplary active front end (AFE) motor drive including a standby controller and an AC pre-charge apparatus with a main contactor for selectively removing power from an LCL filter circuit, an active front end rectifier and an inverter in standby mode in accordance with one or more aspects of the present disclosure; 
           [0008]      FIG. 2  is a simplified schematic diagram illustrating an exemplary fundamental front end (FFE) motor drive with a standby controller operating a main contactor to selectively remove power from a rectifier and an inverter in standby mode; 
           [0009]      FIG. 3  is a schematic diagram illustrating further details of an exemplary AC pre-charge apparatus in the AFE and FFE motor drives of  FIGS. 1 and 2  in which an AC circuit breaker is selectively opened by a standby controller receiving a standby mode command in accordance with the present disclosure; 
           [0010]      FIG. 4  is a schematic diagram illustrating further details of an exemplary rectifier in the motor drives of  FIGS. 1 and 2  in which a rectifier power interface board (PIB) is operated according to the standby controller and a pre-charge power supply selectively provides power to a rectifier main control board; 
           [0011]      FIG. 5  is a schematic diagram illustrating further details of an exemplary inverter in the motor drives of  FIGS. 1 and 2  in which an inverter power interface board (PIB) is operated according to the standby controller and the pre-charge power supply selectively provides power to an inverter main control board; 
           [0012]      FIG. 6  is a simplified schematic diagram illustrating an exemplary common bus inverter drive having a DC pre-charge apparatus with a DC circuit breaker operated according to a standby controller in accordance with further aspects of the disclosure; 
           [0013]      FIG. 7  is a schematic diagram illustrating further details of an exemplary DC pre-charge apparatus in the common bus inverter drive of  FIG. 6 , in which the DC main circuit breaker selectively removes power from an inverter while maintaining power to a pre-charge power supply and a blower supply during standby mode operation in accordance with the present disclosure; 
           [0014]      FIG. 8  is a flow diagram illustrating an exemplary method for operating a motor drive in normal and standby modes in accordance with further aspects of the disclosure; 
           [0015]      FIG. 9  is a simplified schematic diagram illustrating an exemplary non-regenerative six pulse drive with a standby controller in accordance with further aspects of the present disclosure; 
           [0016]      FIG. 10  is a schematic diagram illustrating further details of the motor drive of  FIG. 9  including a contactor for selectively removing power to a converter gate firing circuit during standby mode operation; and 
           [0017]      FIG. 11  is a flow diagram illustrating an exemplary method for operating the non-regenerative motor drive of  FIGS. 9 and 10  in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring now to the figures, several embodiments or implementations of the present disclosure are hereinafter described in conjunction with the drawings, wherein like reference numerals are used to refer to like elements throughout, and wherein the various features are not necessarily drawn to scale. 
         [0019]    Referring initially to  FIGS. 1-5 , exemplary active front end (AFE) and fundamental front end (FFE) embodiments of an AC motor drive ( 100 ) are illustrated and described below in which input AC electrical power (single or multiphase) is received from a power source  10  and output AC electrical power (single or multiphase) is provided to an AC motor load  20 .  FIG. 1  illustrates an AFE drive  100 A having a drive input  101  connecting the AC power source  10  to an AC pre-charge apparatus  110 , and an AC output  112  of the pre-charge apparatus  110  is provided as an input to an LCL filter circuit  120 . An output  122  of the LCL filter is provided as an AC input to an active front end (AFE) rectifier  130 A, which in turn provides a DC output  132  as an input  141  to an inverter  140 . The inverter  140  provides an AC output  142  to drive the motor load  20 . In addition, the AFE drive  100 A of  FIG. 1  includes a standby controller  200  receiving a standby command signal or message  210  from an I/O card or other suitable input, and which generates one or more outputs  202 ,  204 ,  206  to selectively change operation of the pre-charge circuit  110 , the rectifier  130  and/or the inverter  140 , respectively, according to the received standby command  210 . In operation, the AFE rectifier  130 A operates rectifier switching devices S 1 -S 6  ( FIG. 4  below) at a relatively high frequency compared with the fundamental frequency of the AC input source  10 , such as at least about twice the fundamental frequency of the source  10 , and the LCL filter circuit  120  can be optionally included in AFE embodiments to filter the high-frequency switching signals associated with the switching of the rectifier  130 . 
         [0020]      FIG. 2  illustrates a fundamental front end (FFE) motor drive embodiment  100 B in which the input of the rectifier  130 B is connected directly to the AC output  112  of the AC pre-charge apparatus  110  (e.g., no intervening LCL filter circuit  120  as and  FIG. 1 ). In this FFE embodiment, the rectifier  130 B includes rectifier switching devices S 1 -S 6  ( FIG. 4  below) operated at or near the fundamental frequency of the power source  10 . 
         [0021]      FIG. 3  illustrates an exemplary AC pre-charge apparatus  110  provided between the drive input  101  and the downstream rectifier  130  and inverter  140  in the AFE and FFE motor drives  100  of  FIGS. 1 and 2 . The pre-charge apparatus  110  includes a main circuit breaker (switching device)  111  having three contacts connected between the drive input lines “R”, “S”, and “T” and pre-charge output terminals “A”, “B”, and “C”. The circuit breaker  111  is operable in a first mode to allow input power to flow from the power source  10  to the rectifier  130 /inverter  140  and in a second mode to prevent input power from flowing from the power source  10  to the rectifier  130 /inverter  140 , where the mode of the circuit breaker  111  is set according to an input signal from a pre-charge I/O board  118 . In this manner, the breaker  111  closes the connections between the RST input lines and the ABC output lines connected to the subsequent LCL filter  120  (in the AFE embodiments of  FIG. 1 ) or directly to the FFE rectifier  130 B in the embodiment of  FIG. 2 . 
         [0022]    The AC pre-charge apparatus  110  in  FIG. 3  also provides various circuitry for precharging the DC bus capacitors C of the rectifier  130  ( FIG. 4 ), such as at power up or in certain embodiments following resumption of normal mode after a proceeding switch-over to standby mode. In particular, the pre-charge apparatus  110  of  FIG. 3  includes a pre-charge circuit with a pre-charge contactor  114  connected in series with corresponding pre-charge resistors  113  between the input lines RST and the output lines ABC in parallel with the circuit breaker  111 . In addition, the illustrated embodiment further includes a fused disconnect (FD)  115  with 3 connections that are normally closed, but will become open circuits in the event of excessive current flow through the pre-charge circuit. In certain embodiments, moreover the fused disconnect  115  may be omitted. 
         [0023]    The pre-charge apparatus  110  of  FIG. 3  also includes a pre-charge power supply  116  having two AC input lines connected between the fused disconnect  115  and the pre-charge contactor  114 , as well as a door fan  117  which also receives input power from the “R” and “T” input lines downstream of the fused disconnect  115 , but upstream of the pre-charge contactor  114 . The pre-charge power supply  116  provides one or more DC outputs, such as +24 VDC in certain embodiments, to provide control power to the pre-charge I/O board  118  as well as providing control power to main control (MC) boards  134  and  144  of the rectifier  130  and of the inverter  140 , respectively. 
         [0024]    As seen in  FIG. 3 , moreover, the standby controller  200  provides an input signal or message  202  to the pre-charge I/O board  118  of the pre-charge apparatus  110 , which in operation causes the pre-charge I/O board  118  to change the operating mode of the main circuit breaker  111 . In particular, when the standby controller  200  receives an input command  210  indicating a desired change into the standby mode operation for the motor drive  100 , the signal  202  is provided to the pre-charge I/O board  118  so as to open the main circuit breaker  111 , while maintaining the pre-charge contactor  114  also in the open condition. In this standby mode, power is still applied via the fused disconnect  115  from the drive input  101  to the pre-charge power supply  116  and to the door fan  117 , whereby the pre-charge I/O board  118  is provided with DC power from the power supply  116 . As further illustrated in  FIG. 3 , the standby controller  200  provides a signal  204  to the rectifier  130  and provides a signal  206  to the inverter  140  by which these systems  130 ,  140  cease switching operation while maintaining control power from the pre-charge power supply  116  to allow quick resumption of normal mode as discussed further below. At the same time, however, the downstream LCL filter  120  (in the case of an AFE drive as in  FIG. 1  above) as well as the rectifier  130  and inverter  140  are disconnected from the input lines RST via the circuit breaker  111  during standby mode operation. In particular, this causes the DC link voltage at the rectifier output  132  and the inverter input  141  to begin decreasing. 
         [0025]    In addition, as seen in  FIG. 3 , a blower supply  119  is also connected with two of the AC power lines (“A” and “C” in the illustrated example), but the supply  119  is effectively turned off by the I/O board  118  opening the circuit breaker  111  (while maintaining the pre-charge contactor  114  also in the open state) during standby mode operation. In certain embodiments, the blower supply  119  provides powers to one or more air circulation devices (not shown) within the motor drive  100  during normal operation, and the discontinuance of power to these devices further reduces power consumption in the motor drive during standby mode. In certain embodiments, the blower supply  119  includes a control input receiving a 0-10 V control signal from the PIB board  136  of the rectifier  130 , although not a strict requirement of all embodiments. It is noted that in the illustrated embodiment, the door fan  117  remains powered during the standby mode operation, by which a certain amount of cooling can be provided to mitigate overheating of the powered control circuitry (e.g., pre-charge I/O board  118  and pre-charge power supply  116 ). However, this is not a strict requirement of the present disclosure, and in other embodiments the door fan  117  may be omitted or may be connected with two of the to the AC output lines ABC so as to be turned off during standby mode by operation of the circuit breaker  111 . 
         [0026]    In the embodiments of  FIGS. 1-3 , the AC circuit breaker  111  of the pre-charge apparatus  110  is used for selective power reduction during standby mode, and also functions in conjunction with the pre-charge contactor  114  for pre-charging functions in the motor drive  100 . In this regard, the use of the circuit breaker  111  for the disclosed standby mode power reduction functions advantageously employs the breaker  111  without having to introduce new components in the motor drive  100 . In other possible embodiments, however, a separate switching device can be used to selectively discontinue provision of input power from the power source  10  to the rectifier  130  and/or inverter  140  during standby mode operation. In addition, although illustrated in the context of three-phase input power from the source  10  and three-phase intermediate AC power provided to the LCL filter  120  ( FIGS. 1 ) and to the AFE or FFE rectifiers  130 , other embodiments are possible in which single and/or multiphase AC power can be used. In addition, while the illustrated embodiments provide three-phase output power from the inverter output  142  to the motor load  20 , other embodiments are possible in which the inverter  140  provides single or multiphase AC output power to drive a motor load  20 . 
         [0027]    For embodiments equipped with the pre-charge apparatus  110 , the motor drive  100  (whether AFE or FFE) is operable in one of three modes. In each of these modes, the fused disconnect  115  is typically closed, and the contacts thereof will be opened only upon occurrence of an excess current condition. In the normal operating mode, the pre-charge I/O board  118  maintains the main circuit breaker  111  in the closed position (thereby allowing input power to flow from the power source  10  to the precharge output terminals  112 ), but maintains the pre-charge contactor  114  in the “open” condition, whereby no current flows through the pre-charge resistors  113 . In a “pre-charge” mode, the I/O board  118  switches the main circuit breaker  111  into the “open” condition and closes the pre-charge contactor  114 , whereby current flows from the AC source  10  through the pre-charge resistors  113  to the pre-charge output terminals  112 . This facilitates control of excessive current spikes to charge capacitance C of a DC bus formed by the output  132  of the rectifier  130  and/or at the input  141  of the inverter  140  (e.g.,  FIGS. 4 and 5  below). In operation, the pre-charge I/O board  118  may be provided with one or more feedback signals by which a DC link voltage VDC can be monitored, and once this exceeds a predetermined threshold voltage, the I/O board  118  closes the main breaker  111  and opens the pre-charge contactor  114  to enter the normal mode of operation. 
         [0028]    In addition to the “normal” and “pre-charge” modes, the motor drive  100  can be placed into a “standby” operating mode, for example, in response to receipt of a command  210  by the standby controller  200 . In the illustrated embodiments, the “standby” mode can be entered from the “normal” mode, with the standby controller  200  providing a signal  202  to the pre-charge I/O board  118 . In response, the I/O board  118  maintains the pre-charge contactor  114  in the “open” condition, and switches the main circuit breaker  111  into the “open” condition. As discussed above, this disconnects the blower supply  119  as well as the downstream systems coupled with the pre-charge output terminals  112  from the AC input source  10 , but maintains input power to the pre-charge power supply  116  and the door fan  117 . In this standby condition, therefore, the pre-charge power supply  116  provides power to the pre-charge I/O board  118  as well as to the MC boards  134  and  144  of the rectifier  130  and inverter  140 , respectively. This is in contrast to conventional AFE and FFE motor drive operation in which standby mode merely discontinued the switching operation of the rectifier switches S 1 -S 6  ( FIG. 4  below) and of the inverter switches S 7 -S 12  ( FIG. 5 ). Thus, the illustrated standby controller  200  effectively shuts down all nonessential components of the drive while maintaining control power sufficient to allow quick reentry into the normal operating mode if needed. In certain embodiments, moreover, the control input to the blower supply  119  in  FIG. 3  may be reduced to a low-speed level (e.g., 0 V) by the PIB board  136  in the standby condition. 
         [0029]      FIG. 4  illustrates further details of the exemplary rectifiers  130  in the AFE and FFE embodiments of  FIGS. 1 and 2 . Although illustrated is an active rectifier  130 , certain embodiments (e.g., FFE motor drives, etc.) can employ a passive rectifier  130 . The illustrated switching rectifier  130  in  FIG. 4  includes an AC input  112 ,  122  receiving AC input power from the AC pre-charge apparatus  110  (in the case of an FFE drive  100 B as seen in  FIG. 2  above) or the AC input power is received from an intervening LCL filter for the AFE embodiment ( FIG. 1 ). The rectifier  130  provides a DC output  132  including first and second DC output nodes (DC+and DC−, respectively) coupled with corresponding DC current paths  132  by switched operation of a plurality of rectifier switching devices S 1 -S 6  forming a switching network. Each of the rectifier switches S 1 -S 6  is coupled between one of the AC input nodes ABC and one of the DC output nodes DC+, DC−, and the switches S 1 -S 6  are operated according to switching control signals from the rectifier power interface board  136  for conversion of AC input power to DC output power. In operation, the switching control signals are generated by the rectifier main control board  134  and suitable gating control signals are driven by the power interface board  136  or a separate gate driver board (not shown) in normal operation. As mentioned above, moreover, in the case of active front end rectifier operation ( FIG. 1  above), the switching control signals are provided at a frequency higher than a fundamental frequency of the AC input source  10 , and the drive  100 A in this case may include the LCL filter stage  120 . For fundamental front end (FFE) implementations (e.g.,  FIG. 2  above), the main control board  134  generates the rectifier switching control signals at approximately the input fundamental frequency (or a passive rectifier  130  can be used without switching operation). As seen in the example of  FIG. 4 , moreover, the rectifier stage  130  may include one or more output capacitors C connected in any suitable series/parallel configuration, and the illustrated embodiment provides a center node to establish a midpoint voltage between the DC bus terminals  132 , along with balancing resistances RB individually coupled between the center node and the DC output terminals  132 . 
         [0030]    As seen in  FIG. 4 , the standby controller  200  provides a control signal  204  by which the rectifier  130  causes the rectifier main control board  134  to cease generation of the rectifier switching control signals. At the same time, the pre-charge power supply  116  (of the pre-charge apparatus  110  in  FIG. 3  above) maintains power to the main control board  134  to allow quick resumption of normal mode operation if needed. Furthermore, discontinuation of power at the rectifier input terminals ABC allows the DC bus voltage across the capacitance C to discharge, thereby conserving power during standby mode operation, wherein the discharging of the DC bus discontinues power consumption by the balancing resistors RB. 
         [0031]      FIG. 5  illustrates an exemplary three-phase inverter  140  in the motor drives  100  of  FIGS. 1 and 2 , which includes a DC input  141  coupled with the DC output terminals  132  of the preceding rectifier  130 , and provides an AC output  142  having a plurality of AC output nodes UVW coupleable to an AC motor load  20  ( FIGS. 1 and 2  above). In the illustrated embodiment, moreover, the DC input  141  is connected to internal DC capacitances C, which can be any suitable series/parallel combination or a single capacitor, and may include a midpoint node to which internal balancing resistors RB are connected. In certain embodiments, both the output of the rectifier  130  and the input of the inverter  140  are provided with DC bus capacitance and/or balancing resistances, or such may be provided in only one of the rectifier output or the inverter input in other embodiments. In still other embodiments (not shown), the motor drive  100  may be a current source drive in which an intermediate DC link circuit is provided between the rectifier output  132  and the inverter input  141  without any bus capacitance or balancing resistances, but including one or more DC link choke devices. As noted above with respect to the exemplary rectifier  130  of  FIG. 4 , moreover, operation of the standby controller  200  to cause the opening of the main circuit breaker  111  in the pre-charge apparatus  110  ( FIG. 3 ) facilitates reduction in the power consumption of the balancing resistors RB, whether provided in the rectifier  130  or in the inverter  140 . In addition, the illustrated inverter  140  also includes optional output filter components, such as inductors and/or resistors, although not a strict requirement of the present disclosure. 
         [0032]    The inverter  140  also includes an inverter switching network comprising a plurality of inverter switching devices S 7 -S 12  individually coupled between one of the DC input nodes  141  and a corresponding one of the AC output nodes UVW  142 . The inverter switches S 7 -S 12  are operated by corresponding inverter switching control signals generated by the inverter main control (MC) board  144  and driven by the power interface board  146  (or by a separate gate driver board, not shown). As noted above, the standby controller  200  receives the standby mode command  210 , and provides a signal  206  to the inverter  140 , causing the inverter power interface board  146  to discontinue generation of the inverter switching control signals during standby mode operation. At the same time, however, the pre-charge apparatus  110  retains the pre-charge power supply  116  in the “on” condition, and thus the inverter main control board  144  remains powered during the standby mode. This allows the inverter to quickly resume switching operation upon resumption of the normal mode operation in the motor drive  100 . 
         [0033]    The various control components illustrated and described herein, including without limitation the standby controller  200 , the pre-charge I/O board  118 , the rectifier and inverter main control boards  134 ,  144  and components thereof may be implemented as any suitable hardware, processor-executed software, processor-executed firmware, programmable logic, and/or combinations thereof wherein the illustrated embodiment can be implemented largely in processor-executed software or firmware providing various control, signaling, and mode change management functions by which one or more of these components may receive feedback and/or input signals and/or values (e.g., setpoint(s)) and provide the switching control and mode signals to operate the switching devices S 1 -S 6  of the rectifier  130 , the switches S 7 -S 12  of the inverter  140 , and the various circuit breakers and contactors of the pre-charge apparatus  110  according to the functions described herein. In addition, these components  118 ,  134 ,  144 ,  200 , etc., can be implemented in a single processor or one or more of these can be separately implemented in unitary or distributed fashion by two or more processor devices. 
         [0034]    Moreover, the switching devices S 1 -S 12  of the rectifier  130  and the inverter  140  can be any form of electronically actuatable switching devices, such as integrated gate bipolar transistors (IGBTs), silicon controlled rectifiers (SCRs), gate turn-off thyristors (GTOs), gate commutated thyristors ((GCTs) such as integrated gate commutated thyristors (IGCTs) or symmetrical gate commutated thyristors (SGCTs)), etc. 
         [0035]    The mode control command  210  received by the standby controller  200  can be an externally generated signal or message (e.g., received from another system such as a supervisory distributed control system, network, etc., such as through and I/O board, etc.), or the mode command  210  may be set in certain embodiments by the controller  200  based on internal conditions within the motor drive  100 . In addition, the various controllers of the drive  100  may be provided with various feedback information including measured input line-line or line-neutral voltages, sensed AC input line current values, measured DC link voltage values, and/or sensed AC output currents and voltages, etc. In addition, the controllers of the rectifier  130  and of the inverter  140  include suitable interface circuitry in order to receive the various input and/or feedback signals and/or values, as well as suitable driver circuitry for generating switching control signals  162 ,  172 ,  182  of suitable electrical characteristics to actuate the associated switching devices S 1 -S 12  operated according to the signals. The motor drive  100  may also include a user interface (not shown) by which a user may interact with the drive  100  in order to set operating values (e.g., setpoints, mode command  210 ), view sensed operating conditions, etc. 
         [0036]    The switching control signals for the switching devices S 1 -S 12  of the rectifier  130  and/or inverter  140  may be provided using any suitable switching scheme, which may involve one or more pulse width modulation (PWM) techniques including without limitation space vector modulation (SVM), selective harmonic illumination (SHE), etc. In addition, the various control components within the motor drive  100  may operate during normal mode according to one or more setpoints or other signals/values provided by another one of the control components. For instance, the inverter control during normal motoring operation may provide a DC voltage setpoint signal or value to the rectifier  130 , with the rectifier  130  regulating its output voltage according to the setpoint from the inverter  140 . Also, in certain embodiments, the drive  100  may be operated so as to provide regenerative control of power flowing from the load side to the source  10  by selective operation of the switching components of the rectifier  130  and/or of the inverter  140 . 
         [0037]    Referring also to  FIGS. 6 and 7 , another embodiment of a motor drive  100  is illustrated, in this case a “common bus inverter” drive  100 C. In this embodiment, the motor drive  100 C receives a DC input at a drive input  101  from a DC power supply or source  30 , and this DC input power is used to drive an inverter  140 . The inverter  140  may be constructed similar to that described above in connection with  FIG. 5 , and this form of motor drive  100 C allows a single DC source  30  to provide a shared (common) DC bus for use by two or more motor drives  100 C. In certain embodiments, the common bus inverter drive  100 C may include one or both of an initial DC pre-charge apparatus  150  providing an output  152  and/or an optional DC capacitor bank  160  with a DC output  162  provided as an input  141  to the inverter  140 . In addition, the illustrated common bus inverter drive  100 C includes a standby controller  200  substantially as described above. 
         [0038]    As seen in  FIG. 7 , the illustrated DC pre-charge apparatus  150  has input terminals  101  receiving DC input power from the source  30 , and these are coupled to DC output terminals  152  (DC+′ and DC−′, respectively) which provide DC power to the inverter  140  directly or through an optional DC capacitor bank  160  ( FIG. 6 ). As seen in  FIG. 6 , moreover, the standby controller  200  receives a standby mode command  210  (e.g., from an external source in certain embodiments, such as via an I/O card), and in response, provides mode control signals and/or messages  202  and  206  to the pre-charge apparatus  150  and the inverter  140 , respectively. As best seen in  FIG. 7 , the pre-charge apparatus  150  includes a main circuit breaker  151  (a DC breaker in this embodiment) which operates in a first mode to connect the DC source  30  with the pre-charge output terminals  152  or in a second mode to disconnect the DC drive input  101  from the output terminals  152 . 
         [0039]    Pre-charge circuitry is also provided in this embodiment, including a pre-charge contactor  154  connected in series with one or more pre-charge resistors  153  in a series branch that is parallel with the main circuit breaker  151 . As with the above described AC pre-charge apparatus  110  (e.g.,  FIG. 3 ), the DC pre-charge apparatus  150  may include a fused disconnect  155  including normally-closed contacts between the DC input terminals  101  and the contacts of the pre-charge contactor  154 . The common bus inverter drive  100 C, moreover, may include a user-supplied 120 VAC input, which may also pass through corresponding contacts of the fused disconnect  155 , for powering a pre-charge power supply  156 , a door fan  157 , and/or a blower supply  159 . The pre-charge power supply  156  provides DC output power to a pre-charge I/O board  158  (similar in most respects to the I/O board  118  described above in connection with  FIG. 3 ), and also provides DC output power (e.g., 24 VDC) to an inverter MC board  144  of the inverter  140 . 
         [0040]    The pre-charge I/O board  158  controls the operating state of the main circuit breaker  151  and the pre-charge contactor  154  to implement normal, pre-charge, and standby modes generally as discussed above. In the normal mode, the pre-charge I/O board  158  maintains the main circuit breaker  151  in the on or closed position to provide DC current from the source  30  to the output terminals  152 , and in a pre-charge mode opens the main circuit breaker  151  and closes the pre-charge contactor  154  in order to conduct current initially through the pre-charge resistors  153  to limit inrush current while charging the optional DC capacitor bank  160 . 
         [0041]    In response to receipt of a standby command signal or message  210 , the standby controller  200  provides a signal  202  to the pre-charge I/O board  158 , which in turn opens both the main circuit breaker  151  and the pre-charge contactor  154 , whereby no current flows from the DC source  30  to the output terminals  152 . The pre-charge power supply  156 , however, is still connected through the (normally closed) fused disconnect  155  to the user-supplied 120 VAC input, and thus continues to provide a DC output voltage (e.g., 24 VDC) to the pre-charge I/O board  158  and to the inverter power interface board  146 . Also, the standby controller  200  provides the standby signal  206  to the inverter  140 , causing the inverter main control board  144  to discontinue provision of inverter switching control signals to the inverter switching devices (e.g. S 7 -S 12  as shown in  FIG. 5  above). At the same time, as also seen in  FIG. 5 , the pre-charge power supply  156  of the DC pre-charge apparatus  150  provides power to the inverter MC board  144 , whereby this board remains powered to facilitate quick resumption of normal mode operation of the drive  100 C. Moreover, a door fan  157  and a blower supply  159  of the motor drive  100 C remain connected through the fused disconnect  155  to the 120 VAC input, although not a strict requirement of the present disclosure. Other embodiments are possible in which the fused disconnect  155  is omitted. In certain embodiments, the blower supply  159  is equipped with a control input receiving a control signal (e.g., 0-10 V) from the inverter PIB board  146 , and the PIB board  146  in such embodiments may be configured to reduce the level of the control signal (e.g., to 0 V or some other low-speed level) during standby operation in order to further conserve power in the system  100 . 
         [0042]      FIG. 8  illustrates an exemplary method  300  for operating a motor drive, which finds utility in association with multi-mode operation of the above described AFE, FFE and/or common bus inverter type motor drives  100 A- 100 C. Although the exemplary method  300  of  FIG. 8  and the method  400  of  FIG. 11  below are illustrated and described below in the form of a series of acts or events, the various methods of the present disclosure are not limited by the illustrated ordering of such acts or events except as specifically set forth herein. In this regard, except as specifically provided in the claims, some acts or events may occur in different order and/or concurrently with other acts or events apart from those acts or events and ordering illustrated and described herein, and not all illustrated steps may be required to implement a process or method in accordance with the present disclosure. The disclosed methods, moreover, may be implemented in hardware, processor-executed software, programmable logic, etc., or combinations thereof, in order to provide the described functionality, wherein these methods can be practiced in the above described motor drives  100 , although the presently disclosed and methods are not limited to the specific applications and implementations illustrated and described herein. 
         [0043]    At  302  in  FIG. 8 , the motor drive  100  is started, and operation begins in a pre-charge mode at  304  with the main circuit breaker or other switching device or devices (e.g., precharge breakers  111  or  151  in  FIGS. 3 and 7  above) in the non-conducting or “open” condition. The pre-charge mode at  304  also involves maintaining a pre-charge contactor (e.g.  114 ,  154  in  FIGS. 3 and 7 ) and any provided fused disconnect (e.g.,  115 ,  155 ) in the closed or conductive state. A determination is made at  306  in  FIG. 8  as to whether a DC bus voltage VDC is greater than a predetermined threshold “TH”. If not (NO at  306 ), the pre-charge mode continues at  304 . Once the DC bus voltage exceeds the threshold (YES at  306 ), the process  300  proceeds to switch to a “normal” operating mode at  308  (e.g., using the above-described standby controller  200 ). The normal mode proceeds at  310  with the main circuit breaker closed, the pre-charge contactor open, and any provided fused disconnect closed. 
         [0044]    At  312  in  FIG. 8 , a standby command is received (e.g., standby command  210 ), and the switches of the inverter  140  are turned off at  314 , such as by the inverter main control board  144  discontinuing generation of inverter switching control signals, while the inverter power interface board  146  may remain powered to facilitate quick resumption of normal mode operation if needed. At  316 , the switching rectifier  130  (for the case of AFE or FFE drives  100 A and  100 B) is turned off. In the above-described embodiments, for instance, the switching operation of the associated rectifier switching devices S 1 -S 6  is discontinued by the main control board  134 , although the power interface board  136  may remain powered. At  318  in  FIG. 8 , the main circuit breaker is opened, such as by the pre-charge I/O board  118 ,  158  based on receipt of the signal  202  from the standby controller  200 , and the drive  100  thereafter operates in the standby mode at  320  with the main breaker opened, the pre-charge contactor opened, and the fused disconnect closed. This “standby” mode operation continues until receipt of a command at  322  in order to exit the standby mode (e.g., received by the standby controller  200  above). In response, the pre-charge contactor (e.g.,  114 ,  154  in  FIGS. 3 and 7  above) is closed at  324 , and the process  300  returns to the pre-charge mode at  304  as described above. Referring now to the  FIGS. 9-11 , further aspects of the disclosure relate to an exemplary motor drive  100 D, which in certain embodiments may be a non-regenerative six pulse motor drive having an AC input  101  receiving power from an AC source  10  and providing this (directly or indirectly) to the input of a rectifier  130 , which can be generally configured as described in connection with  FIG. 4  above. The rectifier  130  provides a DC output  132  as an input  141  to an inverter  140  that provides an AC output  142  to drive a motor load  20  as previously set forth with respect to  FIG. 5  above. The drive  100 D also includes a standby controller  200  receiving a standby command  210  and providing signals  204  to the rectifier  130  and  206  to the inverter  140 , respectively. As best seen in  FIG. 10 , moreover, the rectifier  130  in this embodiment provides a contactor  131  disposed between two of the three AC input lines RST and a primary of a transformer that drives a converter gate firing board  138  and a blower motor  139  in accordance with a signal  202  from the standby controller  200 . The converter gate firing board  138  in this embodiment provides switching control signals to SCR type rectifier switching devices that convert the input AC from the power source  10  into DC power providing a bus voltage across DC output terminals  132 . In addition, the DC output circuitry of the rectifier  130  may include one or more DC bus capacitances C configured in any suitable series/parallel architecture, as well as one or more balance resistors RB. The output  132  of the rectifier provides the DC input  141  to the inverter  140 , where the inverter  140  may be constructed generally as shown in  FIG. 5  above. 
         [0045]    The motor drive  100 D of  FIG. 10  operates in a normal mode as well as a standby mode. In normal mode operation, the contactor  131  is closed, and the converter gate firing board  138  provides suitable SCR switching control signals to cause conversion of the AC input power to provide DC power to the inverter input  141 . The inverter  140 , in turn, converts this input DC power into AC output currents and voltages suitable for driving a motor load  20 . In response to receipt of the standby signal  210 , the standby controller  200  provides a signal  202  to the contactor  131 , causing the contactor  131  to open. In certain embodiments, moreover, the contactor  131  is opened by the controller  200  only after the DC bus voltage VDC has decayed to a predetermined level. In addition, the standby controller  200  provides a signal  204  to the converter gate firing board  138 , which in turn stops providing switching control signals to the rectifier SCRs, and the signal  204  may be provided to cease rectifier switching prior to the provision of the signal  202  to open the contactor  131  in certain embodiments. Opening the contactor  131  in the illustrated example shuts down both the blower  139  and the converter gate firing board  138  for further power savings during standby operation. Once the converter gate firing board  138  stops providing switching control signals to the rectifier SCRs, the DC bus across the output terminals  132  will begin to discharge, for instance, through the balancing resistors RB. Also, the standby controller  200  provides a signal  206  to the inverter  140 . As discussed above in connection with the example of  FIG. 5 , the inverter  140  receives the signal  206 , and a switching control component (e.g., PIB board  146  in  FIG. 5 ) discontinues switching control signals to the inverter switching devices. By this standby mode operation, the controller  200  conserves power in the motor drive  100 D. 
         [0046]      FIG. 11  illustrates another exemplary method for motor drive operation  400 , which can be employed in the motor drive  100 D of  FIGS. 9 and 10  above. At  402  in  FIG. 11 , the drive  100 D is started, and the contactor  131  is closed at  404 . The drive  100 D proceeds to a pre-charge mode of operation in certain embodiments, and a determination is made at  406  as to whether the pre-charge sequence is completed, such as by detecting that the DC bus voltage across the bus capacitance C has charged to a predefined threshold level. Once this condition is satisfied (YES at  406 ), the motor drive  100 D operates in a “normal” mode at  408  and the blower motor  139  is started at  410 , with the contactor closed and the rectifier and inverter operating for conversion of AC input power to intermediate DC and DC power conversion into AC output power to drive the motor load  20 . 
         [0047]    A standby command is received at  412 , and the controller  200  turns off the rectifier at  414  (e.g., by providing the signal  204  to the converter gate firing board  138 , causing the board  138  to stop firing the SCR&#39;s) and turns off the switching inverter at  416  (e.g., via signal  206  to cause the inverter  142  discontinue the inverter switching control signals). A determination is made at  418  as to whether the DC bus voltage VDC is less than a predetermined threshold. Once this condition has been met (YES at  418 ), the blower  139  is stopped at  420  (e.g., by the standby controller  200  or by the converter gate firing board  138  or other control component of the rectifier  130 ) and the contactor  131  is opened at  422  (e.g. by the standby controller  200  providing the signal  202 ) thereby powering down the blower motor  139  as well as the converter gate firing board  138  for further power savings during standby mode operation. The standby mode operation continues at  424  with the contactor  131  open until a command is received at  426  to exit the standby mode. At this point, the process  400  returns to close the contactor at  404  as described above to begin the pre-charge mode until normal mode can be resumed at  410 . 
         [0048]    Further aspects of the present disclosure provide computer readable mediums with computer executable instructions for implementing the above-described processes and methods. The computer readable medium may be, without limitation, a computer memory, a memory within a power converter control system, a CD-ROM, floppy disk, flash drive, database, server, computer, etc., which has computer executable instructions for performing the processes disclosed above. The above examples are merely illustrative of several possible embodiments of various aspects of the present disclosure, wherein equivalent alterations and/or modifications will occur to others skilled in the art upon reading and understanding this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, systems, circuits, and the like), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component, such as hardware, processor-executed software, logic, or combinations thereof, which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the illustrated implementations of the disclosure. Moreover, the various control components may be implemented using computer-executable instructions for carrying out one or more of the above illustrated and described control operations, steps, tasks, where the instructions are included in a non-transitory computer-readable medium. In addition, although a particular feature of the disclosure may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Also, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in the detailed description and/or in the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.