Abstract:
Diagnostic and/or control methods, systems and apparatuses for variable frequency drives are disclosed. The variable frequency drive may be controlled by a controller that may conduct one or more tests or evaluations. The tests or evaluations may include determining whether a switching device in the variable frequency drive is open-circuited, short-circuited, or operating normally. The tests may include determining whether current provided at an inverter output of the variable frequency drive is within a predetermined range. An exemplary embodiment evaluates the drive for a short circuit condition, an open circuit condition, and a sensor error or failure condition, controls operation of the drive based upon these one or more evaluations, may abort operation of the drive based upon one or more evaluations, and may set a fault code indicative of the type of error encountered.

Description:
BACKGROUND 
       [0001]    Variable frequency drives may handle high voltages and high currents depending on the application. If there are any failures in the variable frequency drive, an individual may be seriously injured or other components of or connected to the variable frequency may be damaged. There is a need to provide diagnostics and/or controls capable of evaluating one or more error or failure conditions of a drive and controlling operation of the drive accordingly. Existing approaches suffer from various shortcomings relative to these and other needs such as the need for cumbersome and expensive equipment, computational complexity and inefficiency, failsafe shortcomings and others. There remains a need for the unique and inventive apparatuses, methods and systems disclosed herein. 
       SUMMARY 
       [0002]    An exemplary embodiment is a diagnostic and control method for a variable frequency drive. The exemplary method evaluates the drive for a short circuit condition, an open circuit condition, and/or a sensor error or failure condition. The exemplary method controls operation of the drive based upon these one or more evaluations. In certain forms the method may abort operation of the drive based upon one or more evaluations. In certain forms the method sets a fault code indicative of the type of error encountered. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for a variable frequency drive. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0003]    The description herein makes reference to the accompanying figures wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0004]      FIG. 1  is a schematic flow diagram of a process for testing a variable frequency drive. 
           [0005]      FIG. 2  is a schematic block diagram of a system including a variable frequency drive. 
           [0006]      FIG. 3  is a schematic flow diagram of a process for determining whether there is a short circuit condition. 
           [0007]      FIG. 4  is a schematic flow diagram of a process for determining whether there is an open circuit condition. 
           [0008]      FIG. 5  is a schematic flow diagram of a process for determining whether there is a sensor error or failure condition. 
           [0009]      FIG. 6  is a schematic block diagram of a controller. 
           [0010]      FIG. 7  is a schematic block diagram of an exemplary chiller system. 
           [0011]      FIG. 8  is a schematic block diagram of an exemplary variable frequency drive. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0012]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0013]      FIG. 1  is a schematic flow diagram of a process  10  for testing a variable frequency drive, which may be performed during a startup mode or at other points of operation of the variable frequency drive. Operations illustrated for all of the processes in the present application are understood to be examples only, and operations may be combined or divided, and added or removed, as well as re-ordered in whole or in part, unless explicitly stated to the contrary. 
         [0014]    Process  10  begins at operation  20 , where a controller in the variable frequency drive receives a signal to start the motor. Before powering and starting the motor, the variable frequency drive conducts a series of tests to ensure that the variable frequency drive is operating correctly. From operation  20 , process  10  proceeds to operation  30 . Operation  30  is a process for determining whether there is a short circuit in the variable frequency drive. For example, operation  30  may determine whether any switching device, such as a transistor, in an inverter of the variable frequency drive is short-circuited. If any switching device is short-circuited, process  10  proceeds to operation  40  in which process  10  is aborted. If none of the switching devices tested are short-circuited, process  10  proceeds to operation  50 . 
         [0015]    Operation  50  determines whether there is an open circuit in the variable frequency drive. For example, operation  50  may determine whether any switching device, such as a transistor, in the inverter of the variable frequency drive is open-circuited. If one or more of the switching device is open-circuited, process  10  proceeds to operation  40  in which process  10  is aborted. If none of the switching devices tested are open-circuited, process  10  proceeds to operation  60 . 
         [0016]    Operation  60  determines whether there are any sensor errors or failures, such as current sensor failures, based on an evaluation of the current flowing in the variable frequency drive. If there is a sensor error or failure, process  10  proceeds to operation  40  in which process  10  is aborted. If there are no sensor errors or failures, process  10  proceeds to operation  70  in which the motor is started and the controller responds with the status of process  10 . 
         [0017]    In operation  40 , in addition to aborting process  10 , the controller may illuminate one or more status indicators that indicate a failure and the type of failure that occurred such as a short-circuited switching device, an open-circuited switching device, or a sensor failure. The status indicator may be an LED that is visible to a technician or another person inspecting the system  100 . In operation  40 , the controller may transmit an error code or the status of the variable frequency drive to an interface for a computer or handheld diagnostic tool to read. The interface may be wired or wireless. The controller may store an error code in its memory. Additionally, the status indicator and/or the error code may provide information that identifies the precise failure that occurred, e.g., the upper U-phase transistor is short-circuited. 
         [0018]    In operation  70 , generally the variable frequency drive will deliver power to the motor if no failure is detected. The controller may illuminate one or more of the status indicators to indicate that the variable frequency drive and/or motor was started successfully. In operation  70 , the controller may transmit a code or status of the variable frequency drive to an interface for a computer and/or handheld diagnostic tool to read. The controller may store a code in its memory. In addition, once the motor is started, the startup mode  10  is exited and control of the variable frequency drive will be conducted in a normal operating mode. 
         [0019]    It is contemplated that only one of the processes  30 ,  50 ,  60  or any combination of the processes  30 ,  50 ,  60  may be used in process  10  to verify that the variable frequency drive is operating correctly. In addition, it is contemplated that other processes and other tests may be used in combination with one or more of the processes  30 ,  50 , and  60 . 
         [0020]      FIG. 2  is a schematic block diagram of a system  100 . The system  100  may be for a heating, ventilating, cooling, or refrigeration (HVACR) system or any other type of system that utilizes a variable frequency drive. The system  100  includes a power supply  102  to supply AC power to a variable frequency drive  104 . The AC power from the power supply  102  is shown as three phase AC power with lines R, S, T, but the AC power may have a different number of phases. 
         [0021]    The variable frequency drive  104  includes a rectifier  106 , a DC bus  108 , and an inverter  110 . The rectifier  106  includes diodes  103  and receives the three phase AC power from the power supply  102 . The rectifier  106  converts the AC power into DC power and supplies the DC power to the DC bus  108 . Although  FIG. 2  illustrates the power supply  102  connected to the rectifier inputs R, S, T, it is contemplated that other circuitry or components such as reactors and/or transformers may be included between the power supply  102  and rectifier inputs R, S, T. The variable frequency drive  104  may also include other circuitry or components such as a metal oxide varistor (MOV)  105 , a capacitor  107 , and/or a resistor  109 . 
         [0022]    The DC bus  108  delivers the DC power to the inverter  110  via two bus rails: a positive DC bus rail  112  and a negative DC bus rail  114 . It shall be understood that the terms positive and negative in this context are relative and that the actual polarities may be both positive, both negative, positive and negative, positive and zero, or negative and zero in various embodiments. The inverter  110  receives DC power from the DC bus  108 , and in particular, the positive DC bus rail  112  and the negative DC bus rail  114 , and converts the DC power into AC power. 
         [0023]    The inverter  114  includes one or more switching devices. For example, the switching device may be one or multiple transistors, a pair of transistors, or multiple pairs of transistors.  FIG. 2  illustrates the switching device as including three pairs of transistors  116 , where each pair of transistors  116  corresponds to one phase of AC power. In the illustrated embodiment, the transistors  116  are insulated gate bipolar transistors. However, it is contemplated that other types of transistors may be used as known to those skilled the art. In addition, the switching device may be another type of electrical component that provides switching functionality other than a transistor. 
         [0024]    Each pair of transistors includes an upper transistor coupled to the positive DC bus rail  112  and a lower transistor coupled to the negative DC bus rail  114 . In particular, transistor  118  is the upper transistor for the U phase, transistor  120  is the lower transistor for the U-phase, transistor  122  is the upper transistor for the V-phase, transistor  124  is the lower transistor for the V-phase, transistor  126  is the upper transistor for the W-phase, and transistor  128  is the lower transistor for the W-phase. 
         [0025]    The system  100  includes two DC bus voltage sensors to measure the voltage on the DC bus  108 . The positive DC voltage sensor  130  measures the voltage on the positive DC bus rail  112 . The negative DC voltage sensor  132  measures the voltage on the negative DC bus rail  114 . 
         [0026]    The system  100  includes three output voltage sensors to measure the output voltage of each phase of the inverter  110 . Sensor  134  measures the output voltage of the U-phase. Sensor  136  measures the output voltage of the V-phase. Sensor  138  measures the output voltage of the W-phase. The output voltage sensors  134 ,  136 ,  138  may be located at a node in electrical communication with the output of its corresponding transistor(s). The output voltage sensors  134 ,  136 ,  138  may be located at corresponding terminals of the inverter or motor. 
         [0027]    The system  100  includes three current sensors to measure the output current in each phase of the inverter  110 . Sensor  140  measures current in the U-phase. Sensor  142  measures current in the V-phase. Sensor  144  measures current in the W-phase. The current sensors  140 ,  142 ,  144  may be located at a node in electrical communication with the output of its corresponding transistor(s). The current sensors  140 ,  142 ,  144  may be located at corresponding terminals of the inverter or motor. In some embodiments, the system  100  includes only two current sensors, e.g., to measure the current in the U-phase and the V-phase. 
         [0028]    The system  100  further includes a controller  146  to control the variable frequency drive  104 , receive measurements from various sensors, and execute instructions or operations in the various techniques disclosed in this application, among other things. The controller  146  is coupled to driver circuitry  148 , which is electrically connected to the gates of each of the transistors  116  (for clarity of illustration the connection is not depicted). This connection allows, among other things, the controller  146  to switch the transistors  116  on and off to generate a pulse width modulated signal or other control signal provided to the motor  150 . The motor  150  may drive a compressor that is part of a HVACR system. 
         [0029]    The controller  146  is also connected to the voltage sensors  130 ,  132 ,  134 ,  136 ,  138  and the current sensors  140 ,  142 ,  144 . Furthermore, the controller  146  is configured with operating logic or instructions to execute the operations in process  10  utilizing the data from voltage sensors  130 ,  132 ,  134 ,  136 ,  138  and current sensors  140 ,  142 ,  144 . In addition, the controller  146  may be coupled to a status indicator  152 , which may be, e.g., one or more light emitting diodes (LEDs). Other embodiments may utilize only two of current sensors  140 ,  142 ,  144 , for example, sensors  140  and  142 . 
         [0030]    Although  FIG. 2  illustrates the inverter output signals U, V, W connected to the motor  150 , other circuitry and/or components such as inductors (not shown) may be included between the inverter outputs and the motor  150 . In addition, although the inverter  110  provides three phase AC power, it is contemplated that the inverter  110  may be reconfigured to supply AC power with a different number of phases. 
         [0031]      FIG. 3  is a schematic flow diagram for a process  30  for determining whether any of the transistors  116  is short-circuited. At operation  31 , the controller  146  switches off all of the transistors  116 . From operation  31 , process  30  proceeds to operation  32 . At operation  32 , the controller  146  receives the voltage readings from one or both of the DC bus voltage sensors  130 ,  132  and one or multiple of the output voltage sensors  134 ,  136 ,  138 . The voltage readings may occur over a period of time, e.g., one power cycle. Moreover, the voltage readings may be an average or a median of multiple readings or a threshold value over a given period of time. 
         [0032]    At operation  33 , the controller  146  compares at least one of the output voltage readings and at least one of the DC bus voltage readings to a reference voltage, such as logic common, to determine voltage differences. It is contemplated that a reference voltage or reference value may be other than logic common as well. 
         [0033]    At operation  34 , the controller  146  determines whether one or multiple of the transistors  116  are short-circuited based on the voltage differences by comparing a voltage difference for one of the three output voltages to one or both of the voltage differences for the two DC bus voltages. For example, if the voltage difference between the U-phase voltage and logic common is approximately the same as the voltage difference between the positive DC bus voltage and logic common, the upper transistor  118  on the U phase is short-circuited because the voltage on the U-phase is being pulled to the voltage on the positive DC bus rail  112  when the transistor  118  is switched off. Similarly, if the voltage difference between the U-phase voltage and logic common is not approximately the same as the voltage difference between the positive DC bus voltage and logic common, the upper transistor  118  on the U-phase is not short-circuited. This comparison may be done for all of the transistors  116  collectively or for each transistor individually to determine if any are short-circuited. Moreover, a short circuit test may be conducted for one or multiple transistors or for one or multiple phases. 
         [0034]    If a transistor  116  is short-circuited, then process  30  proceeds to operation  40 , which, as described above, process  10  is aborted, among other things. If none of the transistors  116  tested are short-circuited, process  10  proceeds to process  50 . 
         [0035]      FIG. 4  is a schematic flow diagram for a process  50  for determining whether any transistor is open-circuited. At operation  51 , the controller  146  switches on transistor  118 . From operation  61 , process  50  proceeds to operation  52 . At operation  52 , the controller  146  receives the voltage reading from the output voltage sensor  134  and the corresponding voltage reading from the DC bus voltage sensor  130 . The voltage readings may occur over a period of time, e.g., one power cycle. Furthermore, the voltage readings may be an average or a median of multiple readings or a threshold value over a given period of time. At operation  53 , the controller  146  compares the two voltage readings to a reference voltage, such as logic common, to determine two voltage differences. It is contemplated that a reference voltage or reference value may be other than logic common as well. 
         [0036]    At operation  54 , the controller  146  determines whether the transistor  118  is open-circuited by determining if the two voltage differences are approximately the same. If the two voltage differences are approximately the same, the transistor  118  is not open-circuited. If the two voltage differences are not approximately the same, then the transistor  118  is open-circuited. This is because when the upper U-phase transistor  118  is switched on, the voltage at the positive DC bus rail  112  should be the same as the voltage of the output of the U-phase. 
         [0037]    If the transistor  118  is open-circuited, then process  50  proceeds to operation  40 , which, as described above, process  10  is aborted, among other things. If the transistor  118  is not open-circuited, process  50  proceeds to operation  55 , which determines whether all of the transistors  116  have been analyzed or whether all of the transistors should be analyzed to determine if they are open-circuited. Process  50  may be repeated for each of the transistors  116  and if none of the transistors  116  tested are open-circuited, process  10  proceeds to process  60 . 
         [0038]      FIG. 5  is a schematic flow diagram for a process  60  for determining whether there is a sensor error or failure. At operation  61 , the controller  146  measures the output current for one or multiple phases of the inverter  110  using the current sensors  140 ,  142 , and/or  144  when the transistors  116  are switched off. The controller  146  confirms that at least one of the currents in one phase is approximately zero amps or within a predetermined range. If the current in a phase is not approximately zero amps or within a predetermined range, the controller  146  may recalibrate the appropriate current sensor  140 ,  142 , or  144 . Once the measured current in the tested phases is approximately zero amps, process  60  proceeds to operation  62 . It is contemplated that operation  61  may not be performed in some implementations. 
         [0039]    From operation  61 , process  60  proceeds to operation  62 . At operation  62 , the controller  146  switches on an upper transistor in one phase such as the upper transistor  118  in the U-phase. From operation  62 , process  60  proceeds to operation  63 . At operation  63 , the controller  146  switches on a lower transistor in another phase such as the lower transistor  124  in the V-phase. 
         [0040]    From operation  63 , process  60  proceeds to operation  64 . At operation  64 , the controller  146  measures the current flowing in the U-phase with the current sensor  140  and measures the current flowing in the V-phase with the current sensor  142 . The current readings for operations  61  and  64  may occur over a period of time, e.g., one power cycle. Furthermore, the current readings may be an average or a median of multiple readings or a threshold value over a given period of time. 
         [0041]    From operation  64 , process  60  proceeds to operation  65 . At operation  65 , the controller  146  determines whether the two current readings are approximately the same, but of opposite polarity. Furthermore, the current should flow through the upper transistor, then through the motor  150 , and then through the lower transistor of the other phase in the opposite polarity. 
         [0042]    If the current readings are not approximately the same and opposite in polarity then a circuit or sensor failure has occurred, and process  60  proceeds to operation  40 , which, as described above, the startup mode  10  is aborted, among other things. If the current readings are approximately the same but in opposite polarity, then process  60  proceeds to operation  66  to determine whether other combinations have been analyzed or should be analyzed such as switching on the upper V-phase transistor  122  and the lower U-phase transistor  120 . In additional embodiments, all three phases may be turned on and the output current may be detected as divided between two phases or doubled depending on whether two of the switches that are turned on are coupled to the positive DC bus or to the negative DC bus. 
         [0043]    In embodiments where the system  100  includes only two current sensors, e.g., to measure the current in the U-phase and V-phase, the above-described analysis may be conducted using the two current sensors to measure current only in two phases. For example, the analysis may be conducted only when the upper U-phase transistor and the lower V-phase transistor are turned on. 
         [0044]    If all of the desired combinations for current analyses have been completed, process  60  proceeds to operation  70  in which the motor  150  is started and the status is reported. For example, the status indicator  152  may be illuminated to indicate the motor  150  has been started. Moreover, the start status may be stored in the memory by the controller  146  where it can be transmitted to another device such as a computer or handheld diagnostic tool. 
         [0045]    In processes  30 ,  50 ,  60 , some of the comparisons or evaluations of voltages and/or currents may refer to “approximately.” As used herein, “approximately” is to generally account for the error or impreciseness of measuring a voltage or current or they may change over small amounts of time. The number of volts or amps that are acceptable under “approximately” depends on the system. In some systems, less than one volt or one amp may be acceptable, but in other systems, several volts or several amps will be within “approximately.” In addition, even if a comparison or evaluation does not refer to “approximately,” the present application presumes that there is an accounting for the impreciseness in the system. 
         [0046]      FIG. 6  is a schematic block diagram of a controller  200 . The controller  200  is one example of a controller configuration which may be utilized in connection with the controller  146  shown in  FIG. 2 . Controller  200  includes a processing device  202 , an input/output device  204 , memory  206 , and operating logic  208 . Furthermore, controller  200  communicates with one or more external devices  210 . 
         [0047]    The input/output device  204  allows the controller  200  to communicate with the external device  210 . For example, the input/output device  204  may be a network adapter, network card, interface, or a port (e.g., a USB port, serial port, parallel port, VGA, DVI, HDMI, FireWire, CAT  5 , or any other type of port or interface). The input/output device  204  may be comprised of hardware, software, and/or firmware. It is contemplated that the input/output device  204  includes more than one of these adapters, cards, or ports. 
         [0048]    The external device  210  may be any type of device that allows data to be inputted or outputted from the controller  200 . For example, the external device  210  may be a handheld computer or diagnostic tool, a computer, a server, a printer, a display, an alarm, an illuminated indicator such as status indicator  152 , a keyboard, a mouse, or a touch screen display. Furthermore, it is contemplated that the external device  210  may be integrated into the controller  200 . It is further contemplated that there may be more than one external device in communication with the controller  200 . The status indicator  152  is one example of an external device  210 . 
         [0049]    Processing device  202  can be of a programmable type, a dedicated, hardwired state machine, or a combination of these; and can further include multiple processors, Arithmetic-Logic Units (ALUs), Central Processing Units (CPUs), Digital Signal Processors (DSPs) or the like. For forms of processing device  202  with multiple processing units, distributed, pipelined, and/or parallel processing can be utilized as appropriate. Processing device  202  may be dedicated to performance of just the operations described herein or may be utilized in one or more additional applications. In the depicted form, processing device  202  is of a programmable variety that executes algorithms and processes data in accordance with operating logic  208  as defined by programming instructions (such as software or firmware) stored in memory  206 . Alternatively or additionally, operating logic  208  for processing device  202  is at least partially defined by hardwired logic or other hardware. Processing device  202  can be comprised of one or more components of any type suitable to process the signals received from input/output device  204  or elsewhere, and provide desired output signals. Such components may include digital circuitry, analog circuitry, or a combination of both. 
         [0050]    Memory  206  may be of one or more types, such as a solid-state variety, electromagnetic variety, optical variety, or a combination of these forms. Furthermore, memory  206  can be volatile, nonvolatile, or a combination of these types, and some or all of memory  206  can be of a portable variety, such as a disk, tape, memory stick, cartridge, or the like. In addition, memory  206  can store data that is manipulated by the operating logic  208  of processing device  202 , such as data representative of signals received from and/or sent to input/output device  204  in addition to or in lieu of storing programming instructions defining operating logic  208 , just to name one example. As shown in  FIG. 6 , memory  206  may be included with processing device  202  and/or coupled to the processing device  202 . For example, the memory  206  may store the code(s) or statuses of a successful or unsuccessful startup as described above. 
         [0051]    The processes  10 ,  30 ,  50 ,  60  may be implemented in operating logic  208  as operations by software, hardware, artificial intelligence, fuzzy logic, or any combination thereof, or at least partially performed by a user or operator. In certain embodiments, modules represent software elements as a computer program encoded on a computer readable medium, wherein the controller  146  performs the described operations when executing the computer program. 
         [0052]      FIG. 7  illustrates an exemplary chiller system that may be used in connection with the system  100 . With reference to  FIG. 7  there is illustrated an exemplary chiller system  700  which includes a refrigerant loop comprising a compressor  710 , a condenser  720 , and an evaporator  730 . Refrigerant flows through system  700  in a closed loop from compressor  710  to condenser  720  to evaporator  730  and back to compressor  710 . Various embodiments may also include additional refrigerant loop elements including, for example, valves for controlling refrigerant flow, refrigerant filters, economizers, oil separators and/or cooling components and flow paths for various system components. 
         [0053]    Compressor  710  is driven by a drive unit  750  including a permanent magnet electric motor  770  which is driven by a variable frequency drive  755 . The permanent magnet electric motor  770  is one example of a motor which may be utilized in connection with the motor  150  shown in  FIG. 2 . Additionally, the variable frequency drive  755  illustrates an exemplary application of the variable frequency drive  104  shown in  FIG. 2 . 
         [0054]    In the illustrated embodiment, variable frequency drive  755  is configured to output a three-phase PWM drive signal, and motor  770  is a surface magnet permanent magnet motor. Use of other types and configurations of variable frequency drives and permanent magnet electric motors such as interior magnet permanent magnet motors are also contemplated. It shall be appreciated that the principles and techniques disclosed herein may be applied to a broad variety of drive and permanent magnet motor configurations. 
         [0055]    Condenser  720  is configured to transfer heat from compressed refrigerant received from compressor  710 . In the illustrated embodiment, condenser  720  is a water cooled condenser which receives cooling water at an inlet  721 , transfers heat from the refrigerant to the cooling water, and outputs cooling water at an output  722 . It is also contemplated that other types of condensers may be utilized, for example, air cooled condensers or evaporative condensers. It shall further be appreciated that references herein to water include water solutions comprising additional constituents unless otherwise limited. 
         [0056]    Evaporator  730  is configured to receive refrigerant from condenser  720 , expand the received refrigerant to decrease its temperature and transfer heat from a cooled medium to the refrigerant. In the illustrated embodiment, evaporator  730  is configured as a water chiller which receives water provided to an inlet  731 , transfers heat from the water to the refrigerant, and outputs chilled water at an outlet  732 . It is contemplated that a number of particular types of evaporators and chiller systems may be utilized, including dry expansion evaporators, flooded type evaporators, bare tube evaporators, plate surface evaporators, and finned evaporators among others. 
         [0057]    Chiller system  700  further includes a controller  760 , which illustrates an exemplary application of the controller  146  shown in  FIG. 2 . Controller  760  outputs control signals to variable frequency drive  755  to control operation of the motor  770  and compressor  710 . Controller  760  also receives information about the operation of drive unit  750 . In exemplary embodiments, controller  760  receives information relating to motor current, motor terminal voltage, and/or other operational characteristics of the motor. It shall be appreciated that the controls, control routines, and control modules described herein may be implemented using hardware, software, firmware and various combinations thereof and may utilize executable instructions stored in a non-transitory computer readable medium or multiple non-transitory computer readable media. It shall further be understood that controller  760  may be provided in various forms and may include a number of hardware and software modules and components such as those disclosed herein. 
         [0058]      FIG. 8  illustrates further details of an exemplary variable frequency drive such as the variable frequency drive  104 . With reference to  FIG. 8  there is illustrated an exemplary circuit diagram for a variable frequency drive  800 . Drive  800  is connected to a power source  810 , for example, a 400/480 VAC utility power supply which provides three-phase AC power to line filter module  820 . Line filter module  820  is configured to provide harmonic damping to mitigate losses which can arise from harmonic feedback from drive components to power source  810 . Line filter module  820  outputs three-phase AC power to a rectifier  890  which converts the AC power to DC power and provides the DC power to a DC bus  891 . The DC bus is connected to inverter  880 . For clarity of illustration and description, rectifier  890 , DC bus  891 , and inverter  880  are shown as discrete blocks. It shall be appreciated, however, that two or more of these components may be provided in a common module, board or board assembly which may also include a variety of additional circuitry and components. It shall be further understood that multiple pulse rectifiers such as 12-pulse, 18-pulse, 24-pulse or 30-pulse rectifiers may be utilized along with phase shifting transformers providing appropriate phase inputs for 6-pulse 12-pulse, 18-pulse, 24-pulse, or 30-pulse operation. 
         [0059]    Inverter module  880  includes switches  885 ,  886  and  887  which are connected to the positive and negative lines of the DC bus  891 . Switches  885 ,  886 , and  887  are preferably configured as IGBT and diode based switches, but may also utilize other types of power electronics switching components such as power MOSFETs or other electrical switching devices. Switches  885 ,  886  and  887  provide output to motor terminals  875 ,  876  and  877 . Current sensors  881 ,  882  and  883  are configured to detect current flowing from inverter module  880  to motor  870  and send current information to ID module  893 . Voltage sensors are also operatively coupled with motor terminals  875 ,  876  and  877  and configured to provide voltage information from the motor terminals to ID module  893 . 
         [0060]    ID module  893  includes burden resistors used in connection with current sensing to set the scaling on current signals ultimately provided to analog to digital converters for further processing. ID module  893  tells the VFD what size it is (i.e. what type of scaling to use on current post ADC) using identification bits which are set in hardware on the ID module  893 . ID module  893  also outputs current and voltage information to gate drive module  850  and also provides identification information to gate drive module  850  which identifies the type and size of the load to which gate drive module  850  is connected. ID module  893  may also provide current sensing power supply status information to gate drive module  850 . ID module  893  may also provide scaling functionality for other parameters such as voltage or flux signals in other embodiments. 
         [0061]    Gate drive module  850  provides sensed current and voltage information to analog to digital converter inputs of DSP module  860 . DSP module  860  processes the sensed current and voltage information and also provides control signals to gate drive module  850  which control signals gate drive module  850  to output voltages to boost modules  851 ,  852  and  853 , which in turn output boosted voltages to switches  885 ,  886  and  887 . The signals provided to switches  885 ,  886  and  887  in turn control the output provided to terminals  875 ,  876  and  877  of motor  870 . 
         [0062]    Motor  870  includes a stator  871 , a rotor  873 , and an air gap  872  between the rotor and the stator. Motor terminals  875 ,  876  and  877  are connected to windings provided in stator  871 . Rotor  873  includes a plurality of permanent magnets  874 . In the illustrated embodiment magnets  874  are configured as surface permanent magnets positioned about the circumference of rotor  873 . The rotor is typically constructed using the permanent magnets in such a way as essentially a constant magnetic flux is present at the surface of the rotor. In operation with rotation of the rotor, the electrical conductors forming the windings in the stator are disposed to produce a sinusoidal flux linkage. Other embodiments also contemplate the use of other magnet configurations such as interior magnet configurations. It shall be understood that interior magnet configurations typically have different inductances in the q-axis and the d-axis. Motor  870  is an exemplary application of motor  150  shown in  FIG. 2 . 
         [0063]    While the invention has been described in connection with what is presently considered to be the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.