Power system architecture for hybrid electric vehicle

An improved power system architecture for a hybrid electric vehicle includes a power control unit including a motor inverter, a generator inverter, and a DC-to-DC converter, and vehicle power management (VPM) circuitry directly connected to each of the motor inverter, generator inverter, and DC-to-DC converter. In this arrangement, communication timing is greatly reduced, thereby allowing for feedforward control of the motor inverter, generator inverter, and DC-to-DC converter. The feedforward control enables the VPM circuitry to predict current influx or draw by a motor and determine the corresponding currents to provide to or from the generator and battery prior to or simultaneously with the actual current influx or draw by the motor. This improves vehicle dynamics and responsiveness, as well as enables complete recapture of braking currents and eliminates the need for a brake chopper resistor, thereby improving overall vehicle efficiency.

TECHNICAL FIELD

This disclosure relates to power system architectures for hybrid electric vehicles and machines.

BACKGROUND

Hybrid electric vehicles and machines include a power system architecture that may include a direct current (DC) bus, a generator, an internal combustion engine to drive the generator, one or more loads such as an electric traction motor, and one or more inverters or converters coupled to the generator and/or electric motor to convert power from DC on the DC bus to alternating current (AC) and vice versa. The generator converts mechanical energy from the engine into electric energy on the DC bus via an inverter in a generation mode. The generator can also operate in the opposite direction in a motoring mode to convert electric energy from the DC bus into mechanical energy via the inverter to assist the engine with other functions on board the vehicle (e.g., raising a bucket hydraulically). The traction motor converts electric energy from the DC bus into mechanical energy via an inverter for use in driving one or more traction elements (e.g., ground-engaging wheels) (“motoring”). Similarly, the traction motor can also operate to convert mechanical energy into electric energy on the DC bus via the inverter (“electric braking”).

The DC bus voltage is subject to large transients introduced by vehicle braking and acceleration and other vehicle dynamics. For example, the electric motor may be commanded to decrease its speed by electric braking so as to generate electric energy that is provided to the DC bus, which may quickly increase the voltage of the DC bus. Similarly, the electric motor may be commanded to increase speed by motoring so as to remove electric energy from the DC bus, which may quickly decrease the voltage of the DC bus. In traditional power system architectures, the system cannot react fast enough to alter the operation of the generator and the battery DC-to-DC converter to accommodate these voltage transients. Thus, to accommodate transients caused by braking, traditional power system architectures typically employ a brake resistor to absorb and release excess voltage transients on the DC bus (e.g., above a voltage threshold) in the form of heat in order to maintain a constant DC bus voltage (e.g., within a range). However, brake resistors and their associated cooling systems add to the cost, weight, and complexity of the vehicle. Additionally, any power dissipated to the brake resistor is lost and represents a system inefficiency. Similarly, with respect to motoring transients, traditional power system architectures may not be able to achieve desired vehicle dynamics and response times and may resort to peak shaving by prioritizing different loads on the system.

SUMMARY

In various embodiments, a hybrid electric vehicle power system includes a power control unit having a DC bus, a first power inverter, a second power inverter, a bi-directional DC-to-DC converter, and vehicle power management (VPM) circuitry. The VPM circuitry is configured to determine or estimate an amount of braking current the first power inverter will input on the DC bus simultaneously with beginning to control the first power inverter in braking mode. Also prior to or simultaneously with beginning to control the first power inverter in braking mode, the VPM circuitry determines or estimates an amount of motoring current to provide to a generator via the second power inverter and an amount of charging current to provide to a battery via the DC-to-DC converter. In this manner, the VPM circuitry uses a feedforward control approach, which enables the VPM circuitry to predict current influx or draw by a motor and determine the corresponding currents to provide to or from the generator and battery prior to or simultaneously with the actual current influx or draw by the motor. This improves vehicle dynamics and responsiveness, as well as enables complete recapture of braking currents and eliminates the need for a brake chopper resistor, thereby improving overall vehicle efficiency.

DETAILED DESCRIPTION

Some power system architectures include one or more batteries coupled to the DC bus to store and provide power in the form of current. Some example power system architectures may utilize a DC bus at a greater or otherwise different voltage from the battery voltage. In such examples, a DC-to-DC converter is employed to convert power from the battery voltage to the DC bus voltage. Thus, in such example systems, current may be provided to the DC bus for use by the electric motor (e.g., during motoring) from the generator and/or from the battery. Similarly, current may also be provided the DC bus during braking of the electric motor, which current may be provided back to the generator and/or the battery.

In certain power system architectures, a generator controller can receive voltage feedback readings of the DC bus voltage to control the generator to try to maintain the DC bus voltage at a nominally constant voltage by use of closed-loop voltage control, such as Proportional/Integral (PI)-based voltage control. In such an arrangement, the generator controller operates the generator in a generating mode to convert mechanical energy into electric energy so as to supply electric energy to the DC bus, or a motoring mode to convert electric energy from the DC bus into mechanical energy so as to remove electric energy from the DC bus to assist the engine with mechanical loads. The generator controller may also control or work in concert with the DC-to-DC converter to supply electric energy from the battery to the DC bus or to store excess electric energy from the DC bus in the battery.

The present disclosure provides an improved power system architecture that greatly reduces or eliminates communication delay between disparate control modules such that overall response time of the power system is improved. In traditional power system architectures, vehicle power management functions are spread across multiple different control modules that are interconnected via, for example, a vehicle communications network (e.g., a controller area network (CAN) bus or a similar communication network or protocol). As such, communications to effect the vehicle power management functions require intercommunication outside of the individual control modules, involving an intermediary communication format that is communicated external to the modules. This intermediary communication format injects delays into the vehicle power management functions. Traditional power system architectures accommodate and account for such communication delays by utilizing brake resistors and large DC bus capacitors to prevent over-voltage and under-voltage conditions on the DC bus caused by power transients due to braking, motoring, or other functions.

In various embodiments of the improved power system architecture, vehicle power management circuitry that controls the motor inverter, the generator inverter, and the DC-to-DC converter is collocated within a single power control unit. In such an arrangement, the vehicle power management circuitry can operate much faster than in traditional power system architectures and is capable of utilizing a feedforward power control arrangement rather than a feedback power control arrangement typically employed in the traditional power system architecture. Similarly, the motor inverter, the generator inverter, and the DC-to-DC converter may also be collocated within the single power control unit to enable direct connection with and control by the vehicle power management circuitry, thereby further increasing the speed at which the power system can react to and/or anticipate power fluctuations and dynamic power needs within the power system.

FIG. 1is an example system diagram of a traditional power system architecture100of a hybrid electric vehicle. The traditional architecture100includes a generator102, an electric machine such as an electric motor104(e.g., a traction motor), a DC bus106, a generator inverter108, and a motor inverter110. Although only one generator102and only one electric motor104are illustrated inFIGS. 1 and 2, the power system architectures100and200may include multiple generators102or multiple motors104. The generator102is electrically coupled to the DC bus via the generator inverter108, and the electric motor104is electrically coupled to the DC bus via the generator inverter108. The generator inverter108and the motor inverter110may be formed in a single inverter module111.

The generator102may be coupled to a powertrain including a power sources such as an engine112configured to provide motive power for the vehicle. The engine112may be configured, for example, as a diesel engine or other internal combustion engine and may operate at a generally constant speed (e.g., 1800 revolutions per minute), although the engine may experience, or be allowed to experience, some minimal speed variation due to, for example, load on the engine or mechanical energy put back on the powertrain and engine112by motoring the generator102.

The engine112may be coupled directly or indirectly to the generator102to establish a mechanical or other connection between the engine112and the generator102. For example, a gearbox114may be coupled between the engine112and the generator102and provides a change in speed between the rotation of the engine112and the generator102. The engine112(or the gearbox114) may have a number of other outputs to provide power to one or more mechanical loads116of the vehicle, such as hydraulic pumps (e.g., to operate a bucket602, seeFIG. 6)), cooling pumps, and cooling fans.

The generator102may be configured to convert mechanical energy into electric energy (“generating mode”), or to convert electric energy into mechanical energy like a motor (“motoring mode”). In the generating mode, the generator102is operable to convert mechanical energy from the engine112into electric energy to supply electric energy onto the DC bus106. In the motoring mode, the generator102is operable to remove electric energy from the DC bus106and convert it into mechanical energy, which may be useful, for example, to assist the engine112with the mechanical loads116such as, for example, operating a hydraulic load (e.g., raise a bucket602hydraulically). In one example, the generator102may take the form of a high-speed three-phase interior-permanent-magnet brushless synchronous generator having three phase coils, or other suitable forms.

Similarly, the electric motor104may be configured to convert electrical energy into mechanical energy (“motoring mode”), or to convert mechanical energy into electric energy (“braking mode”). In the motoring mode, the motor104is operable to consume electric energy from the DC bus106and convert it into mechanical energy. In the braking mode, the motor104is operable to convert mechanical energy into electric energy so as to supply electric energy onto the DC bus106thereby braking (i.e., slowing down) the rotational speed of the motor104and thus the speed of the vehicle. In one example, the motor104may include a three-phase interior-permanent-magnet brushless synchronous motor having three phase coils, or other suitable form, which is operable at a variable speed within a speed range (negative and positive speed limit).

The generator inverter108is electrically coupled to the generator102and the DC bus106and is configured to operate the generator102in generating mode or motoring mode by converting AC power from the generator102to DC power on the DC bus106, and vice versa, according to control signals from inverter control circuitry118, which ultimately controls the power from or to the generator102based on the constraints of the torque and rotational speed.

Similarly, the motor inverter110is electrically coupled to the motor104and the DC bus106and is configured to operate the motor104in motoring mode or braking mode by converting DC power on the DC bus106to AC power for the motor104, and vice versa, according to control signals from the inverter control circuitry118, which ultimately controls the electric motor torque, rotational speed, and direction.

In the traditional power system architecture100, the generator102and generator inverter108may be under the control of the inverter control circuitry118. The inverter control circuitry118may receive a DC bus voltage command from a transmission controller (TCU)120via a communications bus122(e.g., CAN bus) commanding the inverter control circuitry118to control the generator102via the generator inverter108so as to try to maintain the voltage of the DC bus106at a nominally constant voltage (the nominal DC bus voltage) (e.g., 700 VDC). The inverter control circuitry118may receive voltage readings of the actual voltage of the DC bus106from a voltage sensor coupled electrically to the DC bus106. Using closed-loop feedback voltage control, such as Proportional/Integral (PI)-based voltage control, the inverter control circuitry118may operate the generator102in the generating mode or the motoring mode to try to maintain the voltage of the DC bus106nominally at the nominal DC bus voltage. The inverter control circuitry118may determine a generator torque setpoint Tgenat which to operate the generator102via the generator inverter108to achieve the nominal DC bus voltage, and may command operation of the generator102at such setpoint via the generator inverter108.

The motor104and the motor inverter110may be under the control of the inverter control circuitry118. The inverter control circuitry118may receive a torque request from the TCU120. The torque request may be for motoring in the motoring mode or electric braking in the braking mode. The inverter control circuitry118may establish a motor torque setpoint Tmotat the torque request or adjust the motor torque setpoint Tmotfrom the torque request if it determines there is a need to so. The inverter control circuitry118may thereafter command operation of the motor104via motor inverter110at the motor torque setpoint Tmot.

The DC bus106may be coupled to a brake chopper circuit124that controls the flow of current from the DC bus106to a brake resistor126to dissipate excess electric power in the form of heat. The brake resistor126may be cooled via liquid coolant. As discussed above, the brake chopper circuit124may be activated to dissipate excess electric power (transients) on the DC bus106due to the rapid influx of current onto the DC bus106from the motor104via the motor inverter110during motor braking. The inverter control circuitry118may issue pulse-width modulated (PWM) signals to operate a switch (e.g., an insulated-gate bipolar transistor (IGBT)) of the brake chopper circuit124to dissipate the excess power whenever the voltage on the DC bus106exceeds a threshold.

The traditional power system architecture100may also include a battery128electrically coupled to the DC bus106via a DC-to-DC converter130. The battery128may comprise one or more batteries that operate in a range of, for example, 290 volts to 390 volts, with a nominal battery voltage of 320 volts. The DC-to-DC converter130is a bi-directional DC-to-DC converter that is electrically coupled to the DC bus106and the battery128and converts power from the battery128(at 320 volts) to power on the DC bus106(at 700 volts) in a boost mode, and converts power from the DC bus106to power to be stored in the battery128in a buck mode.

The DC-to-DC converter130may be coupled to a DC-to-DC filter132located between the DC-to-DC converter130and the battery128. The DC-to-DC filter132filters ripple on the switched voltage output of the DC-to-DC converter130caused by the switches within the DC-to-DC converter130on the DC lines to the battery128to better condition power to be provided to or from the battery128. In the traditional power system architecture100, the DC-to-DC converter is a separate module from the generator inverter108and motor inverter110in an inverter module111. As such, the DC-to-DC converter130may include DC-to-DC converter control circuitry134to control the operation of the DC-to-DC converter130. The DC-to-DC converter control circuitry134communicates via the communications bus122with an auxiliary control unit136to receive commands to provide power from the battery128to the DC bus106or vice versa.

The traditional power system architecture100also includes a battery management system (BMS)138electrically coupled to the battery128to monitor the status and health of the battery128. The BMS138may communicate battery status and battery health data to the auxiliary control unit136and receive information or commands from the auxiliary control unit136via the communications bus122.

The battery128may be electrically coupled to one or more battery-powered loads140to provide power to the battery-powered loads140. One example battery-powered load140may include an air conditioning unit that may provide air conditioning to the cabin608when the engine112is stopped and/or the vehicle is in battery-only mode. Similarly, a low voltage DC-to-DC converter142may also be electrically coupled to the DC bus106to receive and convert power from the DC bus voltage (e.g., 700 volts) to a low voltage (e.g., 24 volts) to power low voltage loads144and systems within the vehicle. A DC bus filter146is also electrically coupled to the DC bus106and the DC-to-DC converter130to filter harmonic oscillations that may develop on the DC bus106due to the fact that the inverter module111and the DC-to-DC converter130are separate modules and controlled subject to communications delays caused by the communication bus122.

Vehicle power management functions148are represented symbolically inFIG. 1. The vehicle power manager functions148represent a set of control algorithms and functions that are executed through coordinated processing and control by separate modules. For example, the vehicle power manager functions148are executed with coordinated processing involving the TCU120, the inverter control circuitry118, the DC-to-DC converter control circuitry134, and the auxiliary control unit136. As mentioned above, the TCU120may send torque commands for motoring or braking the motor104to the inverter control circuitry118. The inverter control circuitry118may then directly control the motor inverter110to the motor104to accelerate or brake according to the torque commands from the TCU120. Similarly, the inverter control circuitry118may directly control the generator inverter108to generate current from the generator102to the DC bus106, or vice versa, according to the closed-loop feedback voltage control relying on the feedback of the DC bus voltage. Additionally, the inverter control circuitry118may command the DC-to-DC converter130to provide power to the DC bus106from the battery128, or vice versa.

In the traditional power system architecture100, communications between the inverter control circuitry118and the DC-to-DC converter control circuitry134must be converted to a format of the communication bus122and are subject to the protocol of the communication bus122(e.g., according to the CAN bus protocol and format, or another protocol or format). Further such communications must be communicated through the TCU120and/or the auxiliary control unit136before reaching the DC-to-DC converter control circuitry134. The conversion to and from the protocol and format of the communication bus122, and the communication path involving intermediary modules such as the TCU120and the auxiliary control unit136, introduce significant communication delay between the inverter control circuitry118and the DC-to-DC converter control circuitry134(e.g., around 100 ms or higher). The communication delay is greater than the time in which power transients can be introduced on the DC bus106that will exceed an over-voltage trip voltage, for example during motor braking. As such, in the traditional power system architecture100, the DC-to-DC converter cannot begin operating quickly enough to accommodate such transients by storing excess power from the DC bus106in the battery128or providing additional power to the DC bus106from the battery128. Similarly, there is a delay in the time that the generator inverter108can control the generator102to provide current to or remove from the DC bus106due to the mechanical nature of the generator102and the inherent delay involved in utilizing a feedback control scheme based on measuring the DC bus voltage. Further, the amount of current that can be sunk via motoring the generator102is limited or the generator102will begin to fight the power of the engine112. Thus, the traditional power system architecture100relies on the brake chopper circuit124and the brake resistor126, as well as an increased size DC bus capacitor, to accommodate high transients (e.g., during motor braking). Similarly, the traditional power system architecture100relies on an increased motor size to provide the necessary power during peak loads, and peak load shaving control methods to accommodate high power demand transients (which reduce the DC bus voltage). As discussed above, such arrangements are not optimal.

FIG. 2is an example system diagram of an improved power system architecture200of a hybrid electric vehicle in accordance with various embodiments. As with the traditional power system architecture100inFIG. 1, the improved architecture200includes a generator102coupled to a powertrain including the engine112and possibly a gearbox114, either of which may provide power to other mechanical loads116of the vehicle, as discussed above with respect toFIG. 1. Similarly, the improved architecture200includes the electric motor104, which may be coupled to the wheels of the vehicle to move the vehicle (though other uses for the electric motor104are contemplated), as discussed above with respect toFIG. 1. Additionally, the improved architecture includes the battery128, BMS138, DC-to-DC filter132, low voltage DC-to-DC converter142, low voltage loads144, battery-powered loads140, TCU120and auxiliary control unit136, each of which operates largely as discussed with respect toFIG. 1.

Instead of disparate inverter modules and DC-to-DC converter module that communicate and operate across a communications bus122, the improved power system architecture200utilizes a single power control unit202. In certain embodiments, the power control unit202includes a generator inverter204, a motor inverter206, and a DC-to-DC converter208all collocated within the single power control unit202. The generator inverter204operates similarly to the generator inverter108ofFIG. 1in that it is electrically coupled to the DC bus106and configured to control the generator102and provide current to the generator102from the DC bus106(e.g., by motoring the generator102) and to input current from the generator102to the DC bus106(when operating in generating mode). Also, the motor inverter206operates similarly to the motor inverter110ofFIG. 1in that it is electrically coupled to the DC bus106and configured to control the electric motor104and provide current to the electric motor104from the DC bus106(e.g., by motoring the motor104) and to input current from the electric motor104to the DC bus106(e.g., by braking the motor104). Additionally, the DC-to-DC converter208also operates similarly to the DC-to-DC converter130ofFIG. 1in that it is a bi-directional DC-to-DC converter and is electrically coupled to the DC bus106and the battery128and is configured to convert voltage between the DC bus106(e.g., 700 volts) and the battery (e.g., 320 volts).

The single power control unit202also includes vehicle power management (VPM) circuitry210that controls the operation of the power control unit202, including the operation of the generator inverter204, the motor inverter206, and the DC-to-DC converter208. In various embodiments, the VPM circuitry210may comprise a single circuit board or multiple circuit boards that intercommunicate very rapidly utilizing one or more internal computer bus protocols (e.g., inter-integrated circuit bus (IIC), serial peripheral interface (SPI) bus, synchronous serial interface (SSI) bus) or other fast serial or parallel bus communication protocols designed for short distances.

The majority of the vehicle power management functions148discussed inFIG. 1are implemented in the VPM circuitry210of the power control unit202. This centralized VPM circuitry210is unlike the traditional power system architecture100ofFIG. 1, where the vehicle power management functions148where split between the inverter control circuitry118and the DC-to-DC converter control circuitry134, and communications between the inverter control circuitry118and the DC-to-DC converter control circuitry134occurs across an intermediary communications bus122utilizing an intermediary communication format communicated external to either module, and passing through other intermediary modules, thereby introducing significant delay in the control of the different modules. Instead, the single power control unit202inFIG. 2houses all of the control circuitry within the VPM circuitry210, allowing direct connection and direct communication between circuit components and/or software modules that directly control the operations of the generator inverter204, motor inverter206, and DC-to-DC converter208with substantially zero communication delay. In this manner, the power control unit202of the improved power system architecture200is able to operate without the communication delay realized in the traditional power system architecture100. More specifically, the VPM circuitry210is able to rapidly control the DC-to-DC converter208to quickly provide current to the DC bus106from the battery128, and vice versa, as needed with essentially no delay, or at least a negligible delay in comparison to the communication delay in the traditional power system architecture100.

With the reduced or eliminated delay in control, the VPM circuitry210can directly control the DC-to-DC converter208to quickly store the rapid influx of current to the DC bus106caused by motor braking in the battery128, thereby reducing or eliminating rising power transients on the DC bus106. Similarly, the VPM circuitry210can directly control the DC-to-DC converter208to quickly provide current to the DC bus106from the battery128to accommodate rapid power usage by the motor104during motoring (or by other loads), thereby reducing or eliminating low power transients on the DC bus106and improving overall vehicle dynamics and responsiveness.

Because of the increased speed of the VPM circuitry210, the VPM circuitry210is capable of utilizing a feedforward power control arrangement rather than the feedback power control arrangement typically employed in the traditional power system architecture100. The VPM circuitry210receives a motor torque command from the TCU120(e.g., to motor or brake the motor104). The VPM circuitry210is configured to determine (e.g., predict, estimate, or anticipate) the amount of current or power that will be input onto the DC bus106by braking the motor104, or will be consumed by the motor104by motoring the motor104, prior to or simultaneously with the VPM circuitry210beginning to brake or motor the motor104via the motor inverter206. The VPM circuitry210also is aware of the present status and capabilities of the generator102to sink or provide current or power to/from the DC bus106. With this information, during braking, the VPM circuitry210can determine a charging current or power to provide to the battery128from the DC bus106via the DC-to-DC converter208, and a motoring current or power to provide to the generator102from the DC bus106via the generator inverter204prior to or simultaneously with the VPM circuitry210beginning to brake the motor104via the motor inverter206.

For example, during braking, the feedforward current path computation may be Pmotor=Pbatt_ff+Pgen_ffor Imotor=Ibatt_ff+Igen_ff. In certain examples, the amount of current or power the generator102can sink is limited such that the generator102cannot keep up with all of the incoming power from the motor braking. In such examples, the DC bus voltage control is achieved via the battery128. As such, the feedforward path computation can be understood as Pbatt_ff=Pmotor−Pgen. A charging current that the DC-to-DC converter208pulls from the DC bus106and provides to the battery128for storage therein can be determined based on the voltage of either the DC bus or the voltage of the battery, depending on which side of the DC-to-DC converter208is analyzed. For example, the current the DC-to-DC converter208sinks from the DC bus106can be calculated as Ibatt_ff=(Pmotor−Pgen)/VDC_bus, whereas the current the DC-to-DC converter208provides to the battery128can be calculated as Ibatt_ff=(Pmotor−Pgen)/Vbatt.

In one example, the VPM circuitry210predicts (e.g., estimates or anticipates) the current that will be input on to the DC bus106or consumed from the DC bus106by the motor104or the generator102using a lookup table. The lookup table may include values that correspond to the instantaneous speed of the motor104or generator102, the torque demands on the motor104or generator102, and the resulting power or current used by or generated by the motor104or generator102. The lookup table may take into account a known efficiency of the system, which may be static or may vary based on speed or torque. Alternatively, the VPM circuitry210may calculate the predicted currents in real-time using an equation, such as Pmotor=Tmotor×ωmotor, where Pmotorthe power of the motor104, Tmotoris the torque of the is motor104, and ωmotoris the speed of the motor104. The power Pmotormay be multiplied by an efficiency coefficient, (e.g., 0.95) representing a calculated or observed efficiency of the conversion process. The same or similar equation may be used for the generator102as well. Current can of course be derived from power via the power law equation P=V×I.

The VPM circuitry210can repeatedly and/or periodically perform the above feedforward determinations or predictions for the currents throughout the entire braking process, or continuously during operation of the vehicle. In essence, the VPM circuitry210continuously estimates or anticipates power usage and power generation based on control inputs, vehicle conditions, motor104or generator102speed, and real-time actual power usage or generation measurements in a feedforward manner to continuously determine or update currents to provide to and from the generator102and/or the battery128prior to or simultaneously with the actual power usage or generation effected by the motor104or other loads. The VPM circuitry210can also estimate or anticipate the power usage and power generation based on historical or empirical studies, such as stored reference response of braking current versus time during braking mode based on vehicle load, accelerometer measurements, odometer measurements, vehicle ground speed, vehicle velocity, vehicle mass/weight, or other vehicle parameters. Similarly, the VPM circuitry210can estimate or anticipate the power usage and power generation based on historical or empirical studies, such as stored reference response of motoring current versus time during motoring mode based on vehicle load, vehicle velocity, commanded torque, commanded velocity, accelerometer measurements, odometer measurements, drivetrain or transmission gear ratio, fuel metering or regulated fuel input, engine revolutions per minute, vehicle mass/weight, or other vehicle parameters. This information can exist in one or more lookup tables or other data structure formats, which can be stored in the memory318of the VPM circuitry210(seeFIG. 3).

Additionally, after the VPM circuitry210performs the current or power determinations or predictions, and prior to or simultaneously with the VPM circuitry210beginning to brake the motor104via the motor inverter206, the VPM circuitry210can begin controlling the DC-to-DC converter208to begin providing the calculated charging current or power to the battery128from the DC bus106via the DC-to-DC converter208, and begin controlling the generator inverter204to begin providing the calculated motoring current or power to the generator102from the DC bus106via the generator inverter204. In this manner, all of the power or current that is generated by the motor104throughout the entirety of a braking procedure can be provided to the generator102and/or the battery128. This improves the efficiency of the vehicle.

Because the transients on the DC bus106are handled directly by the generator inverter204and DC-to-DC converter208, the brake chopper circuit124and brake resistor126ofFIG. 1are no longer needed and are omitted in the improved power system architecture200ofFIG. 2. Similarly, because the VPM circuitry210can operate quickly to control the DC bus voltage via the generator102and/or the battery128, the power control unit202may also utilize a smaller DC bus capacitor. Additionally, the separate DC-to-DC converter130is eliminated in the improved architecture200, thereby reducing cost and complexity of the vehicle. Also, because the generator inverter108, motor inverter110, and DC-to-DC converter208are all collocated within the single power control unit and controlled by the same VPM circuitry210, the DC bus filter146ofFIG. 1is no longer required, representing further reduction in cost and complexity.

FIG. 3shows an example schematic diagram of a power control unit202of the improved power system architecture200ofFIG. 2in accordance with various embodiments. As discussed above with respect toFIG. 2, the power control unit202includes the generator inverter204, the motor inverter206, the DC-to-DC converter208, the DC bus106, and VPM circuitry210. In certain embodiments, the power control unit202may be a model PD400 Dual Power Inverter manufactured and sold by John Deere (Moline, Ill.).

The generator inverter204may comprise a typical power converter in the form of an AC-to-DC converter, as illustrated, to convert three-phase AC power from the generator102into DC power for the DC bus106. The generator inverter204may include six insulated-gate bipolar junction transistor (IGBT) packages302, each IGBT package302including a diode and an IGBT (operating as a switch). Each IGBT package302may comprise a single diode and IGBT, or multiple packages operating identically in parallel. Respective IGBT packages302may be coupled to a respective one of the generator102phase coils to convert AC power from that coil into DC power on the DC bus106at a nominal voltage of, for example, 700 volts DC between the positive DC power rail304and the negative DC power rail306(which rails together form the DC bus106). When the appropriate voltage is applied to the base of an IGBT of the generator inverter204, the switch (i.e., the IGBT) may be activated and the collector may be coupled electrically to the emitter to pass electric power through the IGBT to the DC bus106. The generator inverter204can be operated in reverse when the generator102is motoring (e.g., to assist the engine112with mechanical loads116) by changing the switching timing of the IGBT packages302.

The motor inverter206may operate in the same manner as the generator inverter204, as a DC-to-AC inverter to convert DC power from the DC bus106into three-phase AC power for the motor104. The motor inverter206may include six IGBT packages308arranged similarly or identically to the six IGBT packages302of the generator inverter204, with respective IGBT packages308coupled to a respective one of the motor104phase coils. When the appropriate voltage is applied to the base of an IGBT of the motor inverter206, the switch (i.e., the IGBT) is activated and the collector may be coupled electrically to the emitter to supply electric power to the respective coil of the motor104to drive the motor. The motor inverter206is operated in reverse to brake the motor104(causing the motor104to operate as a generator) by changing the switching timing of the IGBT packages308.

The DC bus106may also include a DC bus capacitor309connected across the positive DC power rail304and the negative DC power rail306to help maintain the voltage on the DC bus106and filter out ripple caused by switching of the IGBT packages302,308, and310. The DC bus capacitor309may be internal to the power control unit202or may be located external to the power control unit202.

Typically, such a power control unit provides a brake chopper circuit, as discussed with respect toFIG. 1. However, in the improved power system architecture200, the IGBT leg that was previously used for the brake chopper circuit is repurposed and reconfigured as the DC-to-DC converter208. The VPM circuitry210controls the switching of the IGBT packages310of the DC-to-DC converter208to operate the DC-to-DC converter208in a boost mode or a buck mode via PWM switching signals.

In the traditional power system architecture100ofFIG. 1, the outputs of the brake chopper circuit are connected to a brake resistor126to dissipate the power as heat. However, in the improved power system architecture200, those outputs are repurposed for the DC-to-DC converter208and are electrically coupled to the battery128through the DC-to-DC filter132. The DC-to-DC filter132may include one or more inductors312(e.g., one 100 uH inductor) in series with at least one of the output lines, and at least one capacitor314(e.g., two 3.5 mF capacitors) connected across both output lines. The DC-to-DC filter132filters ripple caused by the IGBT packages310within the DC-to-DC converter130on the DC lines to the battery128to better condition power to be provided to or from the battery128. The saturation current of the inductors312may represent the upper limit of the current that can be provided to the battery128(e.g., about 250 amps with the 100 uH inductor).

The power control unit202also includes the VPM circuitry210, which may include one or more processors316, one or more memories318coupled to the processor316, and a set of gate drivers320coupled to the processor316and coupled to and configured to drive the various IGBT packages302,308, and310in the power control unit202via gate signals. The VPM circuitry210receives information and commands from external units, such as the TCU120and/or the auxiliary control unit136and processes data and algorithms. The VPM circuitry210determines the specific control aspects of the generator inverter204, the motor inverter206, and the DC-to-DC converter208and directly controls (e.g., via the gate signals from the gate drivers320) the generator inverter204, motor inverter206, and the DC-to-DC converter208without utilizing communication protocols, formats, or pathways external to the power control unit202.

The VPM circuitry210may be implemented in many different ways and in many different combinations of hardware and software. For example, the VPM circuitry210may include the one or more processors316, such as a Central Processing Unit (CPU), microcontroller, or a microprocessor. Similarly, the VPM circuitry210may include or be implemented with an Application Specific Integrated Circuit (ASIC), Programmable Logic Device (PLD), or Field Programmable Gate Array (FPGA); or as circuitry that includes discrete logic or other circuit components, including analog circuit components, digital circuit components or both; or any combination thereof. The circuitry may include discrete interconnected hardware components or may be combined on a single integrated circuit die, distributed among multiple integrated circuit dies, or implemented in a Multiple Chip Module (MCM) of multiple integrated circuit dies in a common package, as examples. As mentioned above, communication between different circuitry elements and/or modules (e.g., hardware modules or software modules) is implemented via fast data communication protocols or between different software modules within the processor316and is therefore subject only to negligible communication delays, unlike the traditional power system architecture100.

The VPM circuitry210may include the memory318or other tangible storage mediums other than a transitory signal, and may comprise a flash memory, a Random Access Memory (RAM), a Read Only Memory (ROM), an Erasable Programmable Read Only Memory (EPROM), a Hard Disk Drive (HDD), or other magnetic or optical disk; or another machine-readable nonvolatile medium. The memory318may store therein software modules and instructions that, when executed by the processor316, cause the VPM circuitry210to implement any of the processes described herein or illustrated in the drawings. The memory318may also store other data for use by the processor316such as, for example, control reference information for the braking mode and motoring mode, such as reference profiles of braking current or motoring current versus time, which may be based on vehicle load, accelerometer measurements, odometer measurements, vehicle ground speed, vehicle velocity, vehicle mass/weight, commanded torque, commanded velocity, drivetrain or transmission gear ratios, fuel metering or regulated fuel input, engine revolutions per minute, or other vehicle parameters. Such data may be stored in lookup tables or other data structures for storing the reference information and/or other vehicle parameters. In one example, the processor316may execute different software modules consisting of processes and algorithms that are used to control the motor inverter206, the generator inverter204, and the DC-to-DC converter. For example, the processor316(or multiple interconnected processors) may execute a motor inverter control module to control operations of the motor inverter206, a generator inverter control module to control operations of the generator inverter204, and a DC-to-DC converter module to control operations of the DC-to-DC converter208. In certain examples, the different modules may communicate directly within the processor by having direct access to the memory318, or a cache or memory within the processor316, such that communication between the modules is nearly instantaneous. Such instantaneous communication is much faster than the traditional communication methodologies and protocols (e.g., CAN bus) conventionally used to communicate between disparate modules.

FIG. 4shows an example flow diagram of a method400the improved power system architecture ofFIG. 2, and particularly the VPM circuitry210, may implement in accordance with various embodiments. At402, the VPM circuitry210receives a command from the TCU120to begin braking the electric motor104. At404, responsive to receiving the braking command, the VPM circuitry210begins controlling the electric motor in the braking mode, via the motor inverter206, to begin braking. As a result, the motor inverter206inputs a braking current onto the DC bus106generated by the electric motor104.

At406, also responsive to receiving the command to begin braking the electric motor104(step402), the VPM circuitry210determines (e.g., predicts, estimates, anticipates, or calculates) an amount of braking current the motor inverter206will input on the DC bus106from the electric motor104. With this information, at408, the VPM circuitry210determines (e.g., predicts, estimates, anticipates, or calculates) a motoring current or power to provide to the generator102from the DC bus106via the generator inverter204. Similarly, at410, the VPM circuitry210determines a charging current to provide to the battery128from the DC bus106via the DC-to-DC converter208. In one approach, the VPM circuitry210determines the motoring current and the charging current such that the sum of the motoring current and the charging current are substantially equal to the braking current. At412, the VPM circuitry210begins controlling the generator inverter204to begin operating the generator102in the motoring mode to provide the motoring current to the generator102. Similarly, at414, the VPM circuitry210begins controlling the DC-to-DC converter208to begin providing the charging current to the battery128for storage in the battery.

In certain approaches, the VPM circuitry210begins and/or completes steps406,408, and410prior to or simultaneously with the motor inverter206beginning to brake the motor104and beginning to input the braking current on the DC bus106(step404). Also, the VPM circuitry210begins steps412and414prior to or simultaneously with the motor inverter206beginning to brake the motor104and beginning to input the braking current on the DC bus106(step404). In this arrangement, the VPM circuitry210provides feedforward determinations of an amount of current to be absorbed or sunk by each of the generator102and the battery128, and subsequently controls the generator inverter204and the DC-to-DC converter208according to those determinations. This reduces or prevents rising transients on the DC bus106caused by the rapid influx of current from the motor104during braking, and enables capture and reuse of that power generated during braking to improve vehicle efficiency.

In certain embodiments, the braking current includes, at least at some point during a braking operation, a maximum amount of braking current that the motor104can generate during braking and input onto the DC bus106through the motor inverter206. However, despite this maximum influx of current, the VPM circuitry210can still determine the motoring current (to the generator102) and the charging current (to the battery128) such that the sum of the motoring current and the charging current are substantially equal to the braking current. Further, the VPM circuitry210can make this determination through the entire duration of a braking action. In this manner, as shown at416, the VPM circuitry210can control the generator inverter204and the DC-to-DC converter208to sink a maximum amount of braking current that the motor inverter206can input onto the DC bus106throughout the entire duration of the braking action. Similarly, at418and420the VPM circuitry210can control the generator inverter204and the DC-to-DC converter208to sink the maximum amount of braking current that the motor inverter206can input onto the DC bus106while maintaining a voltage of the DC bus106below an over-voltage trip voltage and/or without using a brake chopper resistor. More specifically, in some embodiments of the instant method400, the system does not use a brake chopper resistor during the braking action, as shown in step420. In some embodiments, the over-voltage trip voltage is defined as a set range (e.g., 25, 50, or 75 volts, or a set percentage such as 3%, 5%, 7%, or 10%, or some other specified or designated voltage range or value) in relation to the specified nominal DC bus voltage (e.g., 700 volts). For example, the over-voltage trip voltage may be 750 volts if a maximum of 50 volts over the nominal voltage of 700 volts is selected. In some embodiments, the vehicle can also utilize a traditional mechanical brake to slow or stop the vehicle, for example in emergency situations, such as if a malfunction occurs, or situations where the battery128is fully charged and cannot accept additional charge. Further, in such embodiments, the VPM circuitry210may de-rate the motoring of the electric motor104, possibly to zero, to prevent the influx of current to the DC bus106that cannot be sunk to the battery128or the generator102to prevent over-voltage on the DC bus106.

As discussed above, in certain embodiments, at422, the VPM circuitry210can control the generator inverter204, the motor inverter206, and the bi-directional DC-to-DC converter208via direct connection without communicating via an intermediary communication format communicated external to the power control unit202.

FIG. 5shows another example flow diagram of a method500the improved power system architecture ofFIG. 2, and particularly the VPM circuitry210, may implement in accordance with various embodiments. Whereas the method400ofFIG. 4involves sinking braking current generated by the motor104to the generator102and the battery128, method500involves providing motoring current to the motor104from the generator102and the battery128. At502, the VPM circuitry210receives a command from the TCU120to begin motoring (e.g., accelerating) the electric motor104. At504, responsive to receiving the motoring command, the VPM circuitry210begins controlling the electric motor in the motoring mode, via the motor inverter206, to begin motoring (e.g., accelerating). As a result, the motor104consumes a motoring current from the DC bus106via the motor inverter206.

At506, also responsive to receiving the command to begin motoring the electric motor104(step502), the VPM circuitry210determines (e.g., predicts, estimates, anticipates, calculates, or measures) an amount of motoring current the motor104will consume from the DC bus106via the motor inverter206. With this information, at508, the VPM circuitry210determines (e.g., predicts, estimates, anticipates, calculates, or measures) a generating current or power to provide to the DC bus106from the generator102via the generator inverter204. Similarly, at510, the VPM circuitry210determines a discharge current to provide to the DC bus106from the battery128via the DC-to-DC converter208. In one approach, the VPM circuitry210determines the generating current and the battery discharge current such that their sum are substantially equal to the motoring current provided to the motor104. At512, the VPM circuitry210begins controlling the generator inverter204to control the generator102in the generation mode to begin providing the generating current to the DC bus106. Similarly, at514, the VPM circuitry210begins controlling the DC-to-DC converter208to begin providing the battery discharge current to the DC bus106from the battery128.

In certain approaches, the VPM circuitry210begins and/or completes steps506,508, and510prior to or simultaneously with the motor inverter206beginning to motor the motor104and beginning to consume the motoring current from the DC bus106(step504). Also, the VPM circuitry210begins steps512and514prior to or simultaneously with the motor inverter206beginning to consume the motoring current from the DC bus106(step504). In this arrangement, the VPM circuitry210provides feedforward determinations of an amount of current to be provided by each of the generator102and the battery128, and subsequently controls the generator inverter204and the DC-to-DC converter208according to those determinations, which reduces or prevents low transients on the DC bus106caused by the rapid removal of current to the motor104during motoring or acceleration. Because the battery128and the DC-to-DC converter208can quickly transfer power to the DC bus106(e.g., quicker than the generator102and engine112can react), and because there is substantially no communication delay between the VPM circuitry210and the DC-to-DC converter208, the battery128and the DC-to-DC converter208can react quickly to provide the necessary current to avoid drops in DC bus voltage while allowing the motor104(and any other loads) to consume all the current that is needed. In such an arrangement, peak load shaving can be avoided and overall vehicle dynamics and responsiveness are improved.

In some embodiments, the DC-to-DC converter208may be configured to operate in either a continuous conduction mode (CCM) or a discontinuous conduction mode (DCM), depending on the current conducted through the DC-to-DC converter208. For example, when the DC-to-DC converter208conducts lighter current loads (e.g., below 87.5 Amps) to or from the battery128, the DC-to-DC converter208may operate in the DCM mode (e.g., by utilizing DCM control algorithms). Conversely, with larger current loads, the DC-to-DC converter208may operate in the CCM mode (e.g., by utilizing CCM control algorithms, which are different from the DCM control algorithms). DCM control algorithms generally provide more accurate control over the current output of the DC-to-DC converter208, but are typically only usable with lighter current loads. The VPM circuitry210, and particularly a DC-to-DC converter controller module of the VPM circuitry210, may switch operation of the DC-to-DC converter208between the CCM and DCM modes depending on the current load. However, the VPM circuitry210must handle the transitions between the two modes accurately or the DC-to-DC converter may become unstable. To better anticipate changes between CCM and DCM modes, the VPM circuitry210can utilize the feedforward information regarding the operational demands on the DC-to-DC converter208(e.g., the need to either store or provide current) so that it can determine which operation mode will be required, and if a transition between modes is required, simultaneous with or even before the actual need for the operation mode transition arises. Because the VPM circuitry210utilizes this feedforward information, as opposed to feedback information, the VPM circuitry210can better handle any operation mode transitions in real time to avoid creating instability with the DC-to-DC converter208.

Although the embodiments above discuss control of both the generator inverter204and the DC-to-DC converter208to sink or provide current on the DC bus106at the same time to handle transients caused by quick load changes, in some embodiments or instances, the VPM circuitry210may control only one of the generator inverter204or the DC-to-DC converter208in a prioritized manner to handle the transients. For example, in one approach, if the motor104will quickly require current, the VPM circuitry210can control the DC-to-DC converter208to provide that current from the battery quickly, possibly without affecting the generator102and generator inverter204, at least initially. For example, if the voltage of the DC bus drops below a threshold (e.g., 670 volts), then the VPM circuitry210may then engage the generator inverter204to begin operating the generator102in generation mode to provide additional current. In another approach, if the motor104will begin braking and inputting current onto the DC bus106, the VPM circuitry210may analyze the current mechanical loads116and may first use that incoming current to motor the generator102to provide power to those mechanical loads116rather than saving the power in the battery. Many variations and priority hierarchies are possible. However, persons having skill in the art will understand that the improved power system architecture200is capable of sinking power from and providing power to the DC bus106via both of the DC-to-DC converter208and the generator inverter204simultaneously and according to the above-described feedforward methodology. Additionally, although the system primarily uses the new feedforward approach to current management, a typical feedback system can still be employed, for example, as a backup to ensure the DC bus106maintains a nominal voltage within a set range.

FIG. 6illustrates an example hybrid electric vehicle600that may utilize the improved power system architecture200in accordance with various embodiments. The hybrid electric vehicle600may be a work vehicle (e.g., for construction, forestry, agriculture, or turf) or any other type of vehicle utilizing an electric power system. By way of example, as is shown inFIG. 6, the hybrid electric vehicle600may be a loader601including a bucket602on a front end for digging and dumping material, bucket supports604and hydraulics606for supporting and moving the bucket602, an operator's cabin608, and an engine compartment610in the rear. The loader601may include wheels612and/or a continuous or caterpillar track and may utilize four-wheel drive to move the loader600.

In one embodiment, the improved power system architecture is well suited to provide a feedforward control scheme with improved response time to accommodate power transients on the DC bus during vehicle braking, vehicle acceleration, and other vehicle functions. For example, in certain embodiments, because the vehicle power management circuitry knows how it is controlling the motor (e.g., to brake the motor), it can determine, predict, or measure an anticipated, expected, or actual amount of current that will be or is presently being injected onto the DC bus ahead or time or in real-time with the actual generation of that current. In one approach, such predictions can be based on a lookup table (or other data structures) that takes into account the power, torque, or speed of the motor or generator, as well as the known efficiency of the system or conversion process, which lookup table may be populated with empirical, historical, and/or continuously updated observed or studied acceleration and braking processes for typical operation of the vehicle. Thus, prior to or simultaneously with the actual generation of that current on the DC bus, the vehicle power management circuitry can utilize this feedforward information to determine currents to provide to the generator and/or the battery to accommodate the influx of power generated during braking prior to the influx of current actually occurring. In this manner, the improved power system architecture is capable of capturing, storing, and/or utilizing substantially all power transients on the DC bus caused during braking of the electric motor via the currents provided to the generator (i.e., by motoring the generator to provide power to other mechanical loads) and/or provided to the battery via the DC-to-DC converter. Thus, vehicle efficiency is greatly improved due to ability to store and reuse substantially all power generated during the entirety of a braking operation.

Because all of the current generated on the DC bus during the entire braking process is provided to the generator and/or the battery, the improved power system architecture may also eliminate the brake resistor and associated cooling system, which reduces weight, cost, and complexity of the hybrid electric vehicle and improves overall efficiency. Similarly, because the vehicle power management circuitry can operate quickly to control the DC bus voltage via the generator and/or the battery, the improved power system architecture may also utilize a smaller DC bus capacitor (or bank of capacitors), which also reduces weight and cost of the hybrid electric vehicle.

In one approach, a set of transistors of the single power control unit that were previously used to provide current to the brake resistor (e.g., a brake chopper circuit) in the traditional power system architecture is repurposed to operate as part of the DC-to-DC converter. Because the DC-to-DC converter is collocated with the motor inverter and the generator inverter within the single power control unit, the improved power system architecture eliminates an entire separate DC-to-DC converter module, thereby reducing cost, weight, and complexity of the hybrid electric vehicle. Similarly, the improved power system architecture eliminates an external DC bus filter previously required between the inverters and the DC-to-DC converters. With the traditional power system architecture, the DC bus filter is required to filter harmonic oscillations that may develop on the DC bus due to the fact that the inverters and the DC-to-DC converter are in separate modules and controlled subject to communications delay. Because the inverters and the DC-to-DC converter are all collocated within the single power control unit and controlled by the same vehicle power management circuitry, the DC bus filter is no longer required.

Because the vehicle power management circuitry can control the inverters and DC-to-DC converter with minimal or essentially no delay, the improved power system architecture can quickly provide power when needed and where needed (e.g., during accelerating or lifting a load with a bucket) with little to no delay. This improves the vehicle dynamics (e.g., acceleration, braking, or lifting). Similarly, this also reduces peak shaving requirements within the entire power system. Peak shaving is the reduction of instantaneous power usage by one system (e.g., mechanical loads such as hydraulic lifting) in favor of another system (e.g., motoring by the electric motor) due to prioritization of the various systems' power usage. For example, if the hybrid electric vehicle is accelerating by motoring the electric motor while simultaneously lifting a heavy load via hydraulics, traditional power system architectures may utilize peak shaving to reduce the instantaneous power available to either the motor or the hydraulics to avoid overloading the power system and dropping the DC bus voltage. However, because the improved power system architecture can respond more quickly to instantaneous power needs, power can be provided quickly to whatever load requires it without introducing transients on the DC bus.

Similarly still, the internal combustion engine size can be reduced while maintaining power outputs and vehicle dynamics. With traditional power system architectures, the engine (which drives the generator) is sized to accommodate the largest instantaneous loads via mechanical force. However, the improved power system architecture greatly reduces or eliminates the delay of power provided to the DC bus from the battery such that battery power can be utilized more efficiently and quickly within the system rather than engine power. As such, the size of the engine can be reduced, while peak shaving requirements can be reduced, thereby also improving vehicle dynamics even with a reduced engine size. The reduced engine size reduces the cost and weight of the hybrid electric vehicle, as well as reduces fuel usage and cost and improves overall vehicle efficiency. Additionally still, the vehicle can be operated in a battery-only mode where the engine can be turned off and certain loads (even motoring loads) can be powered by the battery. This reduces fuel usage and costs as well as engine idle hours. Similarly, the vehicle can be operated at a constant fuel consumption level or below a certain fuel consumption maximum level by utilizing battery power when loading on the system would otherwise increase the fuel consumption level. Because the system knows the engine load level, knows the current fuel consumption, and can estimate the future fuel consumption (e.g., when the engine is loaded without using the battery), the system can likewise maintain fuel consumption at or below the current fuel consumption level by supplementing engine power with battery power. This also reduces fuel usage and costs.

So configured, the improved power system architecture200provides technical performance that improve the function and efficiency of the hybrid electric vehicle. For example, communication and control is much quicker, which allows for feedforward control mechanisms. This improves the efficiency of the system by enabling the capture and reuse of excess power developed in the system throughout entire braking actions without dissipating current in a brake resistor. Additionally, weight, cost, and complexity of the vehicle are reduced by eliminating the brake resistor (126), eliminating a separate DC-to-DC converter (130), eliminating a DC bus filter (146), and reducing the size of the DC bus capacitor (309). Further, vehicle dynamics and responsiveness are improved and peak load shaving is reduced.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as illustrative forms of implementing the claims. One skilled in the art will realize that a virtually unlimited number of variations to the above descriptions are possible, and that the examples and the accompanying figures are merely to illustrate one or more examples of implementations. It will be understood by those skilled in the art that various other modifications can be made, and equivalents can be substituted, without departing from claimed subject matter. Additionally, many modifications can be made to adapt a particular situation to the teachings of claimed subject matter without departing from the central concept described herein. Therefore, it is intended that claimed subject matter not be limited to the particular embodiments disclosed, but that such claimed subject matter can also include all embodiments falling within the scope of the appended claims, and equivalents thereof.

In the detailed description above, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter can be practiced without these specific details. In other instances, methods, devices, or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.