Abstract:
A hybrid electric vehicle includes a traction battery, traction motor and power inverter therebetween. The power inverter converts the DC power of the traction battery to AC power to drive each phase of the traction motor. The power inverter includes Insulated Gate Bipolar junction Transistors (IGBTs) to modulate the power to the traction motor. The speed at which the IGBTs are modulated impacts the system performance including power loss, voltage overshoot and current overshoot. Using a dual emitter IGBT to provide a current mirror of the drive current, circuitry may be used with the gate drive circuitry such that the gate drive speed may be dynamically adjusted based on characteristics including temperature and traction motor rotational speed.

Description:
TECHNICAL FIELD 
       [0001]    This application is generally related to control of an IGBT in a traction inverter based on characteristics including a minor current, an IGBT temperature and traction motor rotational speed. 
       BACKGROUND 
       [0002]    Hybrid-electric and pure electric vehicles rely on a traction battery to provide power to a traction motor for propulsion and a power inverter therebetween to convert battery DC power to AC power used by the traction motor. The typical AC traction motor is a 3-phase motor which may be powered by 3 sinusoidal signals each driven with 120 degrees phase separation. The traction motors may require high voltages and high currents. Due to the voltage, current and switching requirements, an Insulated Gate Bipolar junction Transistor (IGBT) is typically used to generate the signals in the power inverter. 
       SUMMARY 
       [0003]    An inverter controller includes a dual emitter IGBT having a gate, a first emitter and second emitter. The first emitter may be configured to flow a load current and a second emitter may be configured to flow a minor current proportional to the load current. The inverter controller further includes a gate driver coupled to the gate and configured to flow a plurality of currents, a buffer circuit to output a buffered signal based on the mirror current, and a latch circuit to output a signal to configure the gate driver to flow a selected current from the plurality of currents in response to the buffered signal and a gate voltage greater than a threshold. 
         [0004]    An inverter controller includes an IGBT having a gate, a first emitter and second emitter, and is configured such that a minor current flowing from the first emitter is proportional to a load current flowing from the second emitter. The inverter controller further includes a variable current voltage control device coupled to the gate, and at least one controller programmed to change a current flow from the variable current voltage control device based on the mirror current. 
         [0005]    A method for controlling a vehicle inverter includes applying a gate voltage to an IGBT, including a first and second emitter, to cause a current flow, sampling a mirror current output from the second IGBT emitter that is proportional to a drive current output from the first IGBT emitter in response to the gate voltage, and changing the current flow to the gate in response to the mirror current and the gate voltage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a diagram of an exemplary hybrid vehicle illustrating typical drivetrain and energy storage components with a power inverter therebetween. 
           [0007]      FIG. 2  is a schematic of an exemplary vehicular electric motor inverter. 
           [0008]      FIG. 3  is a schematic of an exemplary configuration of an IGBT driver with mirror current feedback. 
           [0009]      FIG. 4  is a schematic of an exemplary configuration of an IGBT driver with mirror current feedback and temperature feedback. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
         [0011]      FIG. 1  depicts a hybrid-electric vehicle (HEV)  112 . The hybrid-electric vehicle  112  may comprise one or more electric machines  114  coupled to a hybrid transmission  116 . The electric machines  114  may be capable of operating as a motor or a generator. In addition, the hybrid transmission  116  is coupled to an internal combustion engine (ICE)  118 . The hybrid transmission  116  is also coupled to a drive shaft  120  that is coupled to the wheels  122 . The electric machines  114  can provide propulsion and deceleration capability when the engine  118  is turned on or off. The electric machines  114  also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines  114  may also reduce vehicle emissions by allowing the engine  118  to operate at more efficient conditions (engine speeds and loads) and allowing the hybrid-electric vehicle  112  to be operated in electric mode with the engine  118  off under certain conditions. 
         [0012]    A traction battery or battery pack  124  stores energy that can be used by the electric machines  114 . A vehicle battery pack  124  typically provides a high voltage DC output. The traction battery  124  is electrically connected to one or more power electronics modules. One or more contactors  142  may isolate the traction battery  124  from other components when opened and connect the traction battery  124  to other components when closed. The power electronics module  126  is also electrically connected to the electric machines  114  and provides the ability to bi-directionally transfer energy between the traction battery  124  and the electric machines  114 . For example, a typical traction battery  124  may provide a DC voltage while the electric machines  114  may use a three-phase AC current to function. The power electronics module  126  may convert the DC voltage to produce a three-phase AC current used by the electric machines  114 . In a regenerative mode, the power electronics module  126  may convert the three-phase AC current, from the electric machines  114  acting as generators, to a DC voltage to charge the traction battery  124 . The description herein is equally applicable to a pure electric vehicle. For a pure electric vehicle, the hybrid transmission  116  may be a gear box connected to an electric machine  114  and the engine  118  may not be present. The power electronics module  126  may further include a DC to DC converter having high power switches (e.g., IGBTs) to convert a power electronics module input voltage to a power electronics module output voltage via boost, buck or a combination thereof. 
         [0013]    In addition to providing energy for propulsion, the traction battery  124  may provide energy for other vehicle electrical systems. A vehicle may include a DC/DC converter module  128  that converts the high voltage DC output of the traction battery  124  to a low voltage DC supply that is compatible with other vehicle loads. Other high-voltage electrical loads  146 , such as compressors and electric heaters, may be connected directly to the high-voltage without the use of a DC/DC converter module  128 . The electrical loads  146  may have an associated controller that operates the electrical load  146  when appropriate. The low-voltage systems may be electrically connected to an auxiliary battery  130  (e.g., 12 V battery). The DC/DC converter module  128  may include high power switches (e.g., IGBTs) to convert a DC/DC converter module input voltage to a DC/DC converter module output voltage via boost, buck or a combination thereof. The DC/DC converter module  128  may also operate bi-directionally. 
         [0014]    The vehicle  112  may be an electric vehicle or a hybrid vehicle in which the traction battery  124  may be recharged by an external power source  136 . The external power source  136  may be a connection to an electrical outlet. The external power source  136  may be electrically connected to electric vehicle supply equipment (EVSE)  138 . The EVSE  138  may provide circuitry and controls to regulate and manage the transfer of energy between the power source  136  and the vehicle  112 . The external power source  136  may provide DC or AC electric power to the EVSE  138 . The EVSE  138  may have a charge connector  140  for plugging into a charge port  134  of the vehicle  12 . The charge port  134  may be any type of port configured to transfer power from the EVSE  138  to the vehicle  112 . The charge port  134  may be electrically connected to a charger or on-board power conversion module  132 . The power conversion module  132  may condition the power supplied from the EVSE  138  to provide the proper voltage and current levels to the traction battery  124 . The power conversion module  132  may include high power switches (e.g., IGBTs) to convert a conversion module input voltage to a conversion module output voltage via boost, buck or a combination thereof. The EVSE connector  140  may have pins that mate with corresponding recesses of the charge port  134 . Alternatively, various components described as being electrically connected may transfer power using a wireless inductive coupling. 
         [0015]    The various components discussed may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors. In addition, a system controller  148  may be present to coordinate the operation of the various components. A traction battery  124  may be constructed from a variety of chemical formulations. Typical battery pack chemistries may be lead acid, nickel-metal hydride (NIMH) or Lithium-Ion. 
         [0016]    With reference to  FIG. 2 , a system  210  is provided for controlling a power converter system  212 . The power converter system  212  of  FIG. 2  is shown to include an inverter  214  with first, second, and third phase legs  216 ,  218 ,  220 . While the inverter  214  is shown as a three-phase converter, the inverter  214  may include additional phase legs. For example, the inverter  214  may be a four-phase converter, a five-phase converter, a six-phase converter, etc. In addition, the power converter system  212  may include multiple converters with each inverter  214  in the converter system  212  including three or more phase legs. For example, the system  210  may control two or more inverters  214  in the power converter system  212 . The converter system  212  may further include a DC to DC converter having high power switches (e.g., IGBTs) to convert a power electronics module input voltage to a power electronics module output voltage via boost, buck or a combination thereof. 
         [0017]    As shown in  FIG. 2 , the inverter  214  may be a DC-to-AC converter. In operation, the DC-to-AC converter receives DC power from a DC power link  222  through a DC bus  224  and converts the DC power to AC power. The AC power is transmitted via the phase currents ia, ib, and is to drive an AC machine  226 , such as a three-phase permanent-magnet synchronous motor (PMSM) as depicted in  FIG. 2 . In such an example, the DC power link  222  may include a DC storage battery to provide DC power to the DC bus  224 . In another example, the inverter  214  may operate as an AC-to-DC converter that converts AC power from the AC machine  226  (e.g., generator) to DC power, which the DC bus  224  can provide to the DC power link  222 . Furthermore, the system  210  may control the power converter system  212  in other power electronic topologies. 
         [0018]    With continuing reference to  FIG. 2 , each of the phase legs  216 ,  218 ,  220  in the inverter  214  includes power switches  228 , which may be implemented by various types of controllable switches. In one embodiment, each power switch  228  may include a diode and a transistor, (e.g., an IGBT). The diodes of  FIG. 2  are labeled D a1 , D a2 , D b1 , D b2 , D c1 , and D c2  while the IGBTs of  FIG. 2  are respectively labeled S a1 , S a2 , S b1 , S b2 , S c1 , and S c2 . The power switches with S a1 , S a2 , D a1 , and D a2  are part of phase leg A of the three-phase converter, which is labeled as the first phase leg  216  in  FIG. 2 . Similarly, the power switches with S b1 , S b2 , D b1 , and D b2  are part of phase leg B and the power switches with S c1 , S c2 , D c1 , and D c2  are part of phase leg C of the three-phase converter. The inverter  214  may include any number of the power switches  228  or circuit elements depending on the particular configuration of the inverter  214 . 
         [0019]    As illustrated in  FIG. 2 , current sensors CS a , CS b , and CS c  are provided to sense current flow in the respective phase legs  216 ,  218 ,  220 .  FIG. 2  shows the current sensors CS a , CS b , and CS c  separate from the power converter system  212 . However, current sensors CS a , CS b , and CS c  may be integrated as part of the power converter system  212  depending on its configuration. Current sensors CS a , CS b , and CS c  of  FIG. 2  are installed in series with each of phase legs A, B and C (i.e., phase legs  216 ,  218 ,  220  in  FIG. 2 ) and provide the respective feedback signals i as , i bs , and i cs  (also illustrated in  FIG. 2 ) for the system  210 . The feedback signals i as , i bs , and i cs  may be raw current signals processed by logic device (LD)  230  or may be embedded or encoded with data or information about the current flow through the respective phase legs  216 ,  218 ,  220 . Also, the power switches  228  (e.g., IGBTs) may include current sensing capability. The current sensing capability may include being configured with a current minor output, which may provide data/signals representative of i as , i bs , and i cs . The data/signals may indicate a direction of current flow, a magnitude of current flow, or both the direction and magnitude of current flow through the respective phase legs A, B, and C. 
         [0020]    Referring again to  FIG. 2 , the system  210  includes a logic device (LD) or controller  230 . The controller or LD  230  can be implemented by various types or combinations of electronic devices and/or microprocessor-based computers or controllers. To implement a method of controlling the power converter system  212 , the controller  230  may execute a computer program or algorithm embedded or encoded with the method and stored in volatile and/or persistent memory  234 . Alternatively, logic may be encoded in discrete logic, a microprocessor, a microcontroller, or a logic or gate array stored on one or more integrated circuit chips. As shown in the embodiment of  FIG. 2 , the controller  230  receives and processes the feedback signals i as , i bs , and i cs  to control the phase currents i a , i b , and i c  such that the phase currents i a , i b , and i c  flow through the phase legs  216 ,  218 ,  220  and into the respective windings of the AC machine  226  according to various current or voltage patterns. For example, current patterns can include patterns of phase currents i a , i b , and i c  flowing into and away from the DC-bus  224  or a DC-bus capacitor  232 . The DC-bus capacitor  232  of  FIG. 2  is shown separate from the power converter system  212 . However, the DC-bus capacitor  232  may be integrated as part of the power converter system  212 . 
         [0021]    As shown in  FIG. 2 , a storage medium  234  (hereinafter “memory”), such as computer-readable memory may store the computer program or algorithm embedded or encoded with the method. In addition, the memory  234  may store data or information about the various operating conditions or components in the power converter system  212 . For example, the memory  234  may store data or information about current flow through the respective phase legs  216 ,  218 ,  220 . The memory  234  can be part of the controller  230  as shown in  FIG. 2 . However, the memory  234  may be positioned in any suitable location accessible by the controller  230 . 
         [0022]    As illustrated in  FIG. 2 , the controller  230  transmits at least one control signal  236  to the power converter system  212 . The power converter system  212  receives the control signal  236  to control the switching configuration of the inverter  214  and therefore the current flow through the respective phase legs  216 ,  218 , and  220 . The switching configuration is a set of switching states of the power switches  228  in the inverter  214 . In general, the switching configuration of the inverter  214  determines how the inverter  214  converts power between the DC power link  222  and the AC machine  226 . 
         [0023]    To control the switching configuration of the inverter  214 , the inverter  214  changes the switching state of each power switch  228  in the inverter  214  to either an ON state or an OFF state based on the control signal  236 . In the illustrated embodiment, to switch the power switch  228  to either ON or OFF states, the inverter  214  controls the gate voltage (Vg) applied to each power switch  228  and therefore the switching state of each power switch  228 . Gate voltages Vg a1 , Vg a2 , Vg b1 , Vg b2 , Vg c1 , and Vg c2  (shown in  FIG. 2 ) control the switching state and characteristics of the respective power switches  228 . While the inverter  214  is shown as a voltage-driven device in  FIG. 2 , the inverter  214  may be a current-driven device or controlled by other strategies that switch the power switch  228  between ON and OFF states. The controller  230  may change the gate drive for each IGBT based on the rotational speed of the AC machine  226 , the minor current, or a temperature of the IGBT switch. The change in gate drive may be selected from a plurality of gate drive currents in which the change gate drive current is proportional to a change in IGBT switching speed. 
         [0024]    As also shown in  FIG. 2 , each phase leg  216 ,  218 , and  220  includes two switches  228 . However, only one switch in each of the legs  216 ,  218 ,  220  can be in the ON state without shorting the DC power link  222 . Thus, in each phase leg, the switching state of the lower switch is typically opposite the switching state of the corresponding upper switch. Consequently, a HIGH state of a phase leg refers to the upper switch in the leg in the ON state with the lower switch in the OFF state. Likewise, a LOW state of the phase leg refers to the upper switch in the leg in the OFF state with the lower switch in the ON state. As a result, IGBTs with current minor capability may be on all IGBTs, a subset of IGBTs (e.g., S a1 , S b1 , S c1 ) or a single IGBT. 
         [0025]    Two situations can occur during an active state of the three-phase converter example illustrated in  FIG. 2 : (1) two phase legs are in the HIGH state while the third phase leg is in the LOW state, or (2) one phase leg is in the HIGH state while the other two phase legs are in the LOW state. Thus, one phase leg in the three-phase converter, which may be defined as the “reference” phase for a specific active state of the inverter  214 , is in a state opposite to the other two phase legs, or “non-reference” phases, that have the same state. Consequently, the non-reference phases are either both in the HIGH state or both in the LOW state during an active state of the inverter  214 . 
         [0026]      FIG. 3  is a schematic of an example configuration of a switch driver with a mirror current feedback  300 . The switch  304  may include a MOSFET, an IGBT or similar solid state switch. The switch may be monolithic or may be structured as a multi-chip module. The switch is configured to drive a load current (I Load )  320  and to drive a minor current (I mirror )  332 . The load current may be used to drive a traction motor as part of an inverter or may be used to switch the load current into an inductor as part of a DC-DC power converter. The operation of the switch  304  is controlled by a controller  312 . The controller may be a microprocessor, microcontroller, Application Specific Integrated Circuit (ASIC), Programmable Logic Device (PLD) or may be discrete analog or digital circuitry. The controller may produce a modulation signal, of a form such as a pulse train, pulse width modulated (PWM) or similar, to control the gate modulation. 
         [0027]    The modulation signal may then be developed, in a gate drive conditioning control circuit  310 , by a microprocessor, microcontroller, ASIC, PLD, discrete analog circuitry or discrete digital circuitry. An input to the gate drive conditioning circuit  310  may include a characteristic, such as the minor current  332 , a switch temperature, or a voltage across the switch, determined at a time associated with the switch operation. The time associated with the switch may include a time when the switch is activated and passing current, or a predetermined time before or after the switch is engaged or disengaged. The output of the gate drive conditioning control circuit  310  is the gate drive circuit  302 . 
         [0028]    The gate drive circuit may include a transistor  314  and a current limiting resistor  320  to drive or inject a current on the gate of the switch  304 . This is a commonly referred to as a high-side driver as it connects the gate of the IGBT  304  with Power (Vcc). Likewise, the gate drive circuit may include a transistor  316  and a current limiting resistor  318  to withdraw or extract a current from the gate of the switch  304 . The transistors ( 314 ,  316 ) may be complementary transistors (e.g., N-channel MOSFET and P-channel MOSFET, NPN BJT and PNP BJT, or similar) or may both be of similar structure (e.g., N-channel MOSFETs, NPN BJTs) with the gate edge conditioning circuit  310  including a charge pump to meet the voltage and current needs of the transistors (e.g., N-channel MOSFET). Based on the voltage Vcc, the transistor  314 , the resistor  320  and the potential of the switch, a gate current  334  may flow onto the gate of the switch  304 . The rate at which current flows onto the gate is proportional to the speed at which the switch transitions between the off-state to the on-state. Likewise, based on the voltage Vee, the transistor  316 , the resistor  318  and the potential of the switch, a gate current  334  may flow from the gate of the switch  304 . The rate at which current flows from the gate is proportional to the speed at which the switch transitions between the on-state to the off-state. 
         [0029]    Typically gate resistors (e.g.,  318 ,  320 ) are required in the circuit design to limit the IGBT gate charge/discharge current. In order to control the IGBT switching transient speed in terms of change in load current  330  in relation to change in time (dI/dt) and change in voltage across the switch in relation to change in time (dV/dt), the gate resistors (e.g.,  318 ,  320 ) are usually conservatively chosen. Specifically, an IGBT gate drive design including a large gate resistance (e.g.,  318 ,  320 ) will have slow switching transients, low voltage overshoot (dV/dt) and low current overshoot (dI/dt), however the slow transitioning may result in large switching losses. Alternatively, a small gate resistance (e.g.,  318 ,  320 ) will have a faster switching transient, providing a reduced power loss, however the faster transitioning may result in greater voltage overshoot (dV/dt) and greater current overshoot (dI/dt), along with a possibility of increased Electromagnetic Interference/Electromagnetic Compatibility (EMI/EMC) concerns. Due to reliability concerns, in practice traction inverter designs usually exaggerate the gate resistance in order to guarantee that under worst case scenarios the switching transient resultant voltage overshoot should not exceed the IGBT maximum voltage rating. The IGBT maximum voltage rating is due to IGBTs being vulnerable to over-voltage spikes. For example, if one switching transient resultant voltage spike exceeds the IGBT maximum rated voltage, the voltage spike may cause IGBT avalanche breakdown and permanently damage the IGBT. The exaggerated gate resistance will increase power module switching losses, and as a result, it will impact HEV overall fuel economy as well as add difficulties to power module cooling design. 
         [0030]    A remedy includes a smart gate drive circuit in which the IGBT switching speed may be optimized dynamically. An example of this is illustrated in  FIG. 3 , the circuit  300  includes the gate driver  302 , and the gate driver  302  includes a transistor  322  and associated resistor  328  in parallel with the transistor  314  and associated resistor  320 . This parallel configuration allows increased current to flow onto the gate of the IGBT  304 . The increase in current flow onto the gate is proportional to an increase in transition speed of the IGBT. The increase in transition speed is proportional to a decrease in switching power loss. When the IGBT  304  is turned on with an increased current flow to the gate, a channel is enhanced under the gate allowing the IGBT to saturate resulting in a decrease in voltage across the IGBT  304  (V ce ). The faster decrease in voltage across the IGBT and enhanced channel allow a faster increase in load current flow  330  and mirror current flow  332 . In this example, a pair of transistors ( 314  and  322 ) connected with associated resistors ( 320  and  328 ) configured in parallel are shown, however, this circuit is not limited to this configuration and may include multiple switches (e.g., MOSFETs. BJTs) wherein the BJTs may be connected with associated resistors and the MOSFETs flow current directly to the gate of the IGBT  304  limited by the MOSFET&#39; s channel on resistance, (R on ). 
         [0031]    The gate drive conditioning circuit  310  may comprise at least one AND gate to drive the transistor  322  based on an enable signal and the modulation signal. The gate drive conditioning circuit  310  may comprise an OR gate to drive the transistor  324  based on the inverse of the enable signal and the modulation signal Likewise, the gate drive conditioning circuit  310  may comprise at least one buffer, driver, tri-state buffer, AND gate or OR gate of an inverting or non-inverting type to drive the transistors ( 314 ,  316 ,  322  and  324 ) based on an enable signal and the modulation signal. 
         [0032]    A complementary example is also illustrated in  FIG. 3 , the circuit  300  includes the gate driver  302 , and the gate driver  302  includes a transistor  324  and associated resistor  326  in parallel with the transistor  316  and associated resistor  318 . This parallel configuration allows increased current to flow from the gate of the IGBT  304 . The increase in current flow from the gate is proportional to an increase in transition speed of the IGBT. The increase in transition speed is proportional to a decrease in switching power loss. When the IGBT  304  is turned off with an increased current flow from the gate, shutting off the switch  304  results in a faster increase in voltage across the IGBT  304 , and a faster decrease in load current flow  330  and minor current flow  332 . 
         [0033]    The minor current  332  may be buffered in a minor current buffer circuit  308  to produce a buffered minor current  334 . The mirror current buffer circuit  308  may include a filter such as a low pass filter, a band-pass filter, a notch filter or a high pass filter. The filter may be a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (IIR) filter or other appropriate filter. The buffered minor current  334  may be sampled or latched in a latch circuit  306 . The latch circuit  306  may be based on the gate voltage of the IGBT  304 . The latch circuit  306  may include a filter such as a low pass filter, a band-pass filter, a notch filter or a high pass filter to filter the gate voltage or appropriate control signal. The filter may be a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (IIR) filter or other appropriate filter. A latched buffer minor current signal  336  may be provided to the gate edge conditioning circuit  310  as an input to determine a desired rate of change of the switch  304 . The latched buffer mirror current signal  336  may be used directly as an enable signal to enable additional current sources to drive the IGBTs (e.g.,  314 ,  316 ,  322  and  324 ) or may be an input to the controller  312  which is used to generate an enable signal based on more complex conditions. 
         [0034]      FIG. 4  is a schematic of an exemplary configuration of an IGBT driver with minor current feedback and temperature feedback. Similar to  FIG. 3 ,  FIG. 4  includes a current minor configuration to provide feedback and to be used as input to a gate drive conditioning circuit  402 . However,  FIG. 4  also comprises a temperature sensor  410 . The temperature sensor  410  may be monolithic (i.e., fabricated in the same semiconductor device) or may be a separate sensor thermally coupled to the IGBT. A separate sensor thermally coupled with the IGBT may be within a multi-chip module (MCM) or may be a discrete sensor placed in proximity with the IGBT. 
         [0035]    The IGBT temperature sensor  410  may produce a buffered IGBT temperature signal  416  in an IGBT temperature buffer circuit  414  based on the temperature sensor  410 . The IGBT temperature buffer circuit  414  may include a filter such as a low pass filter, a band-pass filter, a notch filter or a high pass filter to filter the signal from the temperature sensor. The filter may be a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (IIR) filter or other appropriate filter. The buffered IGBT temperature signal  416  may be sampled or latched in a temperature latch circuit  412 . The temperature latch circuit  412  may be based on the gate voltage of the IGBT  404  or the controller  312  may control the temp latch circuit  412 . The temperature latch circuit  412  may include a filter such as a low pass filter, a band-pass filter, a notch filter or a high pass filter to filter the gate voltage or appropriate control signal. The filter may be a Finite Impulse Response (FIR) filter, an Infinite Impulse Response (IIR) filter or other appropriate filter. The latched buffer IGBT temperature signal  418  may be provided to the gate drive conditioning circuit  402  as an input to determine a desired rate of change of the switch  404 . The latched buffer IGBT temperature signal  418  may be used directly as an enable signal to enable additional current sources to drive the IGBTs (e.g.,  314 ,  316 ,  322  and  324 ) or may be an input to the controller  312  which is used to generate an enable signal based on more complex conditions. 
         [0036]    The processes, methods, or algorithms disclosed herein can be deliverable to/implemented by a processing device, controller, or computer, which can include any existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms including, but not limited to, information permanently stored on non-writable storage media such as Read Only Memory (ROM) devices and information alterably stored on writeable storage media such as floppy disks, magnetic tapes, Compact Discs (CDs), Random Access Memory (RAM) devices, and other magnetic and optical media. The processes, methods, or algorithms can also be implemented in a software executable object. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), Field-Programmable Gate Arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
         [0037]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.