Patent Application
20110144840
1. Field of the Invention
The present invention relates generally to hybrid electric vehicles and is particularly concerned with a propulsion energy storage and control system and method for a hybrid electric vehicle.
2. Related Art
A hybrid electric vehicle (or “HEV”) is a vehicle which combines a conventional propulsion system with an on-board rechargeable propulsion energy storage system to achieve better fuel economy and cleaner emissions than a conventional vehicle. While HEVs are commonly associated with automobiles, heavy-duty hybrids also exist. In the U.S., a heavy-duty vehicle is legally defined as having a gross weight of over 8,500 lbs. A heavy-duty HEV will typically have a gross weight of over 10,000 lbs. and may include vehicles such as a metropolitan transit bus, a refuse collection truck, a semi tractor-trailer, or the like.
The efficiency and emissions of a HEV depend on the particular configuration of the subsystems making up the hybrid power system and the control system which integrates the subsystems. Existing HEVs often have complex integration systems which increase the cost of such vehicles.
HEV configurations fall into two basic categories: series and parallel. In a parallel configuration, either an internal combustion engine or an electric motor can apply torque to turn the wheels. Electrical energy is stored in an energy storage device, such as a battery pack or an ultracapacitor pack, and may be used to assist the drive wheels as needed, for example during acceleration. In a series configuration, the internal combustion engine (ICE) drives a generator which can charge the propulsion energy storage and/or power the electric drive motor. In a series configuration there is no mechanical coupling of the engine drive shaft and the drive wheels. An advantage of series HEVs is that the ICE can be located anywhere in the vehicle because it does not transmit power mechanically to the wheels. In contrast, parallel configurations must connect both the motor and the ICE engine to the drive train, generally requiring the motor and engine to be aligned and close to one another.
Energy storage packs in hybrid vehicles, particularly heavy duty vehicles, reside in a harsh operating environment and face unique challenges not present in non-vehicular applications. In particular, the environment is hot, dirty, and subject to vibration. As such, individual cells within an energy storage pack may be more susceptible, among other things, to vary from cell to cell compared to stationary applications. For example, different cells may charge at different rates and individual cells may deteriorate at a faster rate than other cells within a pack. In addition, due to the very high voltages in which some heavy duty hybrid vehicles operate, there are unique challenges in controlling the energy storage packs in such vehicles. Current multi-cell energy storage implementations include integrated cell balancing, voltage monitoring, and temperature monitoring, but leave room for improvement. Another problem with existing energy storage packs and associated control systems is that additional energy storage modules cannot readily be added to an existing system if more power is needed. Instead, a completely new system must be designed for each vehicle having different energy storage requirements.
Embodiments described herein provide an energy storage system and method for a hybrid electric vehicle having a series or parallel hybrid drive configuration. According to one aspect, a propulsion energy storage system specially adapted for a hybrid electric vehicle comprises at least a first energy storage module, a system controller configured to communicate with the hybrid electric vehicle via a vehicle communication bus, and a controller communication bus communicatively coupled with the system controller and with the first module controller for communications between the first module controller and system controller. The energy storage module may then have a first plurality of energy storage cells, a first energy storage cell communication link, and a first module controller configured to communicate with the first plurality of energy storage cells via the first energy storage cell communication link. In one embodiment, a low voltage power supply of the vehicle provides power for the system controller and the first module controller is powered by the first plurality of energy storage cells. While it may seem counterintuitive and unnecessarily complex, the inventors have found that a serial communication protocol stack and supporting system architecture as described below, actually provides multiple advantages in controlling a propulsion energy storage in a heavy duty hybrid electric vehicle.
In one embodiment, the system comprises a plurality of energy storage modules, each energy storage module having a respective module controller communicating with the system controller via the controller communication link and with the energy storage cells of the associated energy storage module via a respective energy storage cell communication link. Each module controller is powered by the energy storage cells of the respective energy storage module with which it is associated, and may comprise a processor coupled with individual energy storage cells and with various sensors in the energy storage module proximate the cells.
An electrical isolator may be located between each module controller and the controller communication bus to electrically isolate communications between the module controllers and controller communication bus.
In one embodiment, the system controller communicates over the vehicle communication bus using a first protocol and over the controller communication bus using a second protocol which is simpler than the first protocol. The module controller communicates over the controller communication bus using the second protocol and over the energy storage cell communication link using a third protocol which is simpler than the second protocol. In one embodiment, the first protocol is a controller area network (CAN), the second protocol is a local interconnect network (LIN), and the third protocol is a serial peripheral interface (SPI).
In this system, the main or overall system controller communicates with the vehicle and with the one or more module controllers and may also be programmed to carry out various system diagnostics such as determining the state of charge and state of health of the energy storage modules. Each module controller may be configured to measure the voltage between cells, and to balance the cells during charging and discharging. The module controllers may also be configured to measure module current and ground isolation.
According to another aspect, a method of controlling propulsion energy storage of a hybrid electric vehicle comprises providing power to a system controller from a low voltage power supply of the hybrid electric vehicle, providing power to at least a first energy storage module controller of a first energy storage module from a first plurality of energy storage cells associated with the first energy storage module, communicating in a first protocol between the system controller and the hybrid electric vehicle via a vehicle communication bus, and communicating in a second protocol between at least the first energy storage module controller and the system controller via a controller communication bus. In one embodiment, the method further comprises communicating in a third protocol between the first energy storage module controller and the first plurality of energy storage cells via a first energy storage cell communication link.
Due to the high voltages and complex communications between a power supply and a hybrid electric vehicle, an isolated, complex communication protocol is needed. By providing separate system controllers and energy storage module controllers, communications can be separated into different communication levels or tiers for control communications within individual energy storage modules, control communications between the energy storage modules and an overall system controller, and the higher level communications required between the system controller and the hybrid electric vehicle network. Thus, simpler communication protocols can be used for the lower level communications. In one embodiment, a high level communication network or broadcast serial network such as CAN is used as the first protocol over the vehicle communication bus. A lower level protocol such as LIN is used as the second protocol for communications between the system controller and storage module controllers, and an even simpler protocol such as SPI is used for communications within individual energy storage modules.
Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying drawings.
The details of the present invention, both as to its structure and operation, may be gleaned in part by study of the accompanying drawings, in which like reference numerals refer to like parts, and in which:
After reading this description it will become apparent to one skilled in the art how to implement the invention in various alternative embodiments and alternative applications. However, although various embodiments of the present invention are described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this detailed description of various alternative embodiments should not be construed to limit the scope or breadth of the present invention as set forth in the appended claims.
The components illustrated in
Unique to a HEV, the vehicle will typically have both a high voltage electrical system and a low voltage electrical system. Hybrid drive system 100 provides the vehicle's high voltage system, which is partially illustrated in
In addition to the high voltage power supply, the HEV also has a low voltage or auxiliary power supply which is used as the power supply of the starter that starts ICE engine 112, various low power vehicle devices such as a radio and lights, and various system controllers. The low voltage system is defined herein and being below 50 VDC, but will typically comprise a 12 VDC, 24 VDC, or 48 VDC power supply. The low voltage system is akin to the electrical system of a conventional (non-hybrid) vehicle.
Power from the propulsion energy storage 120 may solely power the one or more electric propulsion motor(s) 134 or may augment power provided by the engine genset 110. To appreciate the power level involved, heavy-duty HEVs may operate off a high voltage electrical power system rated at, for example, over 500 VDC. Similarly, propulsion motor(s) 134 for heavy-duty vehicles (here, having a gross weight of over 10,000) may include, for example, two AC induction motors that produce 85 kW of power (×2) and having a rated DC voltage of 650 VDC. The propulsion energy storage system may include one or more energy storage modules, as described in more detail below and in connection with
Unlike lower-rated electrical systems, heavy-duty high power HEV drive system components may also generate substantial amounts of heat. Due to the high temperatures generated, high power electronic components such as the generator 114 and electric propulsion motor(s) 134, for example, are typically cooled (e.g., water-glycol cooled), and may also be included in the same cooling loop as the ICE 112.
As a key added feature of HEV efficiency, many HEVs recapture the kinetic energy of the vehicle via regenerative braking rather than dissipating kinetic energy via friction braking. In particular, regenerative braking (“regen”) is where the electric propulsion motor(s) 134 are switched to operate as generators, and a reverse torque is applied to the drive wheel assembly 132. In this process, the vehicle is slowed down by the main drive motor(s) 134, which converts the vehicle's kinetic energy to electrical energy. As the vehicle transfers its kinetic energy to the motor(s) 134, now operating as a generator(s), the vehicle slows and electricity is generated and stored by the energy storage 120. When the vehicle needs this stored energy for acceleration or other power needs, it is released from energy storage 120. This is particularly valuable for vehicles whose drive cycles include a significant amount of stopping and accelerating (e.g., metropolitan transit buses). Regenerative braking may also be incorporated into an all-electric vehicle (EV) thereby providing an onboard source of electricity generation (recapture).
When the propulsion energy storage 120 reaches a predetermined capacity (e.g., fully charged), the drive wheel propulsion assembly 130 may continue to operate in regen for efficient braking However, instead of storing the energy generated, any additional regenerated electricity may be dissipated through a resistive braking resistor 140. Typically, the braking resistor 140 is included in the cooling loop of the ICE 112, and dissipates the excess energy as heat.
Certain embodiments as disclosed herein provide for a propulsion energy storage system specially adapted for a hybrid electric vehicle, which includes a control system having multiple tiers of communication using different protocols, and which allows for addition and removal of energy storage modules without changing the system controller. In particular, the energy storage control system and method of the embodiments that follow form a tiered system such that monitoring and control functions for the energy storage system can be separated from the vehicle-level monitoring and control functions. The tiered communication architecture described herein may include direct and bus communications. The control and monitoring functions are tiered within the energy storage system between a system controller, powered by vehicle auxiliary power, and one or more individual energy storage module controllers, powered by the energy storage cells in their respective modules.
The system controller and module controllers are coordinated to control operation of the energy storage cells according to system requirements. In one embodiment, the system controller communicates with the vehicle via a first communication bus, and communicates with the module controller or controllers via a second communication bus. Additionally, the module controllers communicate with energy storage cells within the respective modules via a third communication link or bus. The tiered energy storage control system, separated from the vehicle controller, gives the system a plug-n-play appearance to the vehicle, and the modular design allows additional energy storage modules to be added on or energy storage modules to be removed easily without requiring any modification to the vehicle control system.
With regard to controls, in the past, energy storage units themselves have been non-intelligent, and typically only included the energy storage device (e.g., batteries or ultracapacitors), and possibly also some sensors, cooling fans, and/or internal balancing circuitry, all packaged in a housing. Prior energy storage units were also highly integrated into the vehicle propulsion system. The energy storage unit was then controlled by a vehicle or drive system controller, essentially using switches that would electrically couple and de-couple the energy storage to and from the DC bus 150 such that energy/power could be transferred to or from the energy storage unit. In contrast, the architecture illustrated in
The next control tier includes one or more module controllers. In particular, each energy storage module 220A, 220B, 220C, having a plurality of energy storage cells 122, further includes a module controller 262A, 262B, 262C, respectively. The module controllers 262A to 262C communicate with the system controller 260 via energy storage controller communication bus 272, and communicate with their respective energy storage cells 122 (and any associated sensors and control circuits) via a module communication link or third tier data link 274A, 274B, 274C, respectively. Examples of suitable module controllers are the ADuC703x family of highly integrated, precision battery monitors manufactured by Analog Devices of Norwood, Mass. The individual module controllers 262A to 262C are powered directly by the energy storage cells 122, as illustrated by pack power lines 278. Since each module controller is powered by its own respective module, the vehicle's auxiliary power is not needed to power the module controller, and therefore no electrical coupling is necessary. In this way, maintaining electrical isolation between the high voltage and low voltage systems is greatly simplified. Additionally, this provides for expansion without extra electrical hardware on the vehicle.
In addition to stratifying the control architecture, the system may also include different tiers of communication. In particular, the vehicle communicates to the system controller 260 via bus communications, the system controller 260 communicates with the individual module controllers 262A to 262C via bus communications, and the individual module controllers 262A to 262C communicate within the module via bus and/or direct communications. This tiered communication strategy provides for an expandable energy storage pack/system where energy storage modules 220 may be added or removed without changing the system controller. In addition, module controllers 262A to 262C++?
Each different communication tier may communicate differently. In particular, different communication protocols may be used for the various communication links or buses in the system of
Since the energy storage system requires a lower level of communications than is needed for the entire vehicle, the communication protocol used for the energy storage or controller communication bus 272 may be simpler than that of the vehicle communication bus or CAN bus 270, Preferably, in one embodiment, the protocol for controller communication bus 272 may form a local interconnect network (LIN). Likewise, since each module is a self contained unit and doesn't need to expand, the communication protocol used for the module communication bus or data link 274A to 274C may be even simpler than that of the controller communication bus 272. Preferably, in one embodiment, a broadcast serial network or serial peripheral interface (SPI) protocol may be used for each module data link 274.
In the system of
The plurality of energy storage cells 122 in each module may be electrically coupled in series, increasing the pack's voltage. Alternately, energy storage cells 122 may be electrically coupled in parallel, increasing the pack's current, or both in series and parallel. Any suitable energy storage cells may be used in modules 220, such as ultracapacitors as described in U.S. Pat. No. 7,085,112 and U.S. patent application Ser. No. 11/460,738, the contents of each of which are incorporated herein by reference. Energy storage cells 122 may alternatively be battery based, or the like. Individual module controllers 262A, 262B, 262C, respectively, communicate with the energy storage cells 122 in the respective module via the module communication link 274A, 274B, 274C, respectively, for data transfer, and also communicate with various sensors proximate the cells via the same link. The sensors may comprise sensors used for monitoring or controlling energy storage cell parameters and are not shown in detail in the drawings. For example, the energy storage modules 220 may include overvoltage protection circuitry and cell balancing circuits as described in copending application Ser. No. 12/237,529 filed on Sep. 25, 2008, the contents of which are incorporated herein by reference, as well as pre-charge relays, on-off relays, balancing resistors and various pack monitoring sensors as described in U.S. patent application Ser. No. 11/460,738 and U.S. Pat. No. 7,085,112 referenced above.
As noted above, the system controller 260 is powered by the vehicle's low voltage auxiliary power system, while the energy storage modules are part of a high voltage system. In view of this, the system controller 260 and controller communication bus 262 are electrically isolated from the energy storage modules via isolator modules or circuits 263, as illustrated in
In a single-wire full-duplex application, the isolator module may be configured to distinguish original system controller signals and energy storage module signals from each other, so that only original system controller signals are passed across the electrical isolator from left to right to the module controller, as illustrated in
In the example illustrated in
As discussed above, the architecture of energy storage system 205 is much more readily adjustable to add or remove energy storage packs (e.g., 220A to 220n+1) than prior art systems, which generally require, at a minimum, modification of the vehicle controller in order to allow such modifications to be made. As indicated in
According to one embodiment, the system controller 260 may control the electrical coupling of the energy storage modules to and from the high voltage DC bus 150 via energy storage system contactors (or switches) 405 and 406. In addition to their control function, these dual switches 405, 406 also aid in increasing electrical isolation protection. In addition, although not illustrated, each module 220 may further include a module fire system configured to report and/or extinguish energy storage fires or fire conditions, a safety electrical disconnect of the module configured to manually safe the energy storage, and individual module contactors configured to electrically couple and de-couple the module.
According to one embodiment, each energy storage module 220A, 220B, and 220C may also include a dedicated cooling module 318A, 318B, and 318C, respectively. As illustrated, each cooling module may include a heat exchanger and a cooling device, such as a fan or blower. Cooling modules 318A, 318B, and 318C may operate as part of a open loop system or a closed loop system. Moreover, cooling modules 318A, 318B, and 318C may be coupled with a vehicle heat exchanger or vehicle cooling system (not shown) to simplify the heat exchanger of the cooling module. For example, dedicated cooling modules 318A, 318B, and 318C may include the energy storage pack cooling system as described more fully in copending application Ser. No. 12/343,970 filed on Dec. 24, 2008, the contents of which are incorporated herein by reference.
According to one embodiment, sensors such as temperature sensors may be located proximate the cells and/or throughout the module. The cooling device may be switched on automatically if the detected temperature in the module is above a predetermined level, and switched off when the temperature falls below a threshold level. The cooling modules 318A to 318C may be controlled by their respective module controllers or by the system controller. As such, the cooling device may be switched on upon receiving a command from either, responsive to a measured temperature or other criteria.
As illustrated here, the series of energy storage cells 122 in each energy storage module 220A to 220C, as well as any associated sensors and control circuits, are represented collectively by cell modules 415A, 415B and 415C. Each cell module is shown having a cell balancing module 408 configured to monitor and balance the energy storage cells within the module. The cell balancing circuit or module 408 may be embodied by hardware, software, or a combination of both, and may alternately be incorporated in the module controllers 262A-C or may be a separate component in each energy storage module. Additionally, the series of energy storage cells 122 may be arranged in strings (not shown), whereas the cell balancing module 408 may be embodied as one or more circuits integrated with the strings of energy storage cells 122.
In one embodiment, cell balancing circuitry or cell balancing and protection circuitry 408 is provided in each energy storage module 220A-C to monitor and protect the energy storage cells 122 in the respective energy storage module and to balance charges between the storage cells according to a desired operational configuration corresponding to a set of predetermined measurement parameters. Cell balancing is very important to the health of the energy storage and may dramatically affect its useful life. Each cell balancing circuit is electrically coupled to each energy storage cell of a string. Where plural strings are involved, each module may have a single cell balancing circuit coupled to each cell in each of the strings, or a separate cell balancing circuit may be coupled with each string. Each cell balancing circuit is configured to measure the voltage level of each cell and to actively balance the voltages between the energy storage cells based on an operating configuration determined from a current set of measurement parameters, as described in more detail below. The module controllers 262A to 262C control the cell balancing circuit to balance the energy storage cells according to the latest operating configuration. As above, each cell balancing circuit may be incorporated into the respective module controller 262A, 262B, or 262C, or may be independent but communicatively coupled with the respective module controller via the associated data communication link 274A, 274B, or 274C. In addition, cell balancing and protection circuitry 408 may determine voltage, temperature and other cell information, which may be then used to determine SOC and protect against faults and failures.
As discussed above, the system controller 260 is configured or programmed to communicate with the vehicle and to communicate with one or more module controllers 262A-C. In one embodiment, the system controller 260 may be configured to determine the state of charge (SOC) and state of health (SOH) of the energy storage modules based on sensor outputs received from the module controllers 262A-C. In another embodiment, the system controller 260 may also be configured to also to carry out comprehensive diagnostics. The diagnostics may include pre-operation diagnostics, e.g. self-check of individual energy storage pack components, operation diagnostics, and historical/statistical diagnostics. The operation diagnostics may include real-time operation diagnostics such as checking for conditions such as overvoltage, pack electrical isolation, pack seal breach, and state of charge of individual cells in each pack or energy storage module. The diagnostics may be carried out based on inputs received from the individual storage module controllers 262A to 262C, cell balancing and protection circuitry 408, ICs 508A, and/or inputs from other vehicle components or subsystems. The system controller 260 may also be configured to control the pack or energy module contactors or switches 405, 406, the module cooling systems 318A, 318B, 318C, and the energy module pre-charge circuits (not illustrated).
According to one embodiment, the method would include electrically isolating communications between the module controller(s) and the controller communication bus, wherein the electrical isolation further comprises distinguishing original system controller signals and isolated energy storage signals from each other, such that only original system controller signals are passed across an electrical isolator to the respective module controller and only isolated energy storage signals are transmitted out of the electrical isolator to the controller communication bus.
According to one embodiment, the communication method may further include providing certain communications between the hybrid electric vehicle and the system controller 260. In particular, the system controller 260 will preferably include communicating the state of charge (SOC) and state of health (SOH) of the propulsion energy storage system 205. This information may be used by the drive system to optimize its efficiency and performance. Likewise, this information may be logged or reported to maintenance personnel. According to one embodiment, the method may further include the system controller 260 and hybrid electric vehicle communicating a comprehensive diagnosis of at least part of the propulsion energy storage system 205, where the comprehensive diagnosis includes at least one of pre-operation diagnostics, operation diagnostics and historical/statistical diagnostics, as discussed in greater detail below.
This control system and method provides tiered high, mid, and low level communications and separates vehicle-level communications/control functions from the energy storage system communications/control functions, making the system more modular and more readily expandable. This is different from existing energy storage systems and control of such systems, which are typically integrated with the vehicle control system so that the energy storage system cannot be modified without also requiring modification of the vehicle control system to adapt to the expanded energy storage system.
As indicated in box 708 of
The system controller 260 may also be configured to operate the system/module contactors, pre-charge circuit of the propulsion energy storage, module cooling systems, system/module fire systems, and safety electrical disconnect of the system or individual modules. The system controller 260 may also provide system contactor feedback to the HEV and provide reports of system/module performance and system/module fault conditions to the HEV.
As indicated in box 710 of
As indicated in box 710, during operation, each module controller 262 may continue to comprehensively diagnose module operation, monitoring for overvoltage conditions, isolation of the high voltage system, module seal breach, SOC of the module, and fault conditions. The module controller 262 also operates to actively balance the cells in its module, as described above in connection with
Both levels of controller may also be configured to carry out historical/statistical diagnostics over time (Step 712). This may comprise logging or reporting system and module operating parameter determinations, states, performance characteristics, and faults.
Those of skill will appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein can often be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the design constraints imposed on the overall system. Skilled persons can implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the invention. In addition, the grouping of functions within a module, block or step is for ease of description. Specific functions or steps can be moved from one module or block without departing from the invention.
Various illustrative logical blocks and modules described in connection with the embodiments disclosed herein can be implemented or performed with a general purpose processor, a digital signal processor (DSP), application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor can be a microprocessor, but in the alternative, the processor can be any processor, controller, microcontroller, or state machine. A processor can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium. An exemplary storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The processor and the storage medium can reside in an ASIC.
The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein can be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is to be understood that the description and drawings presented herein represent a presently preferred embodiment of the invention and are therefore representative of the subject matter which is broadly contemplated by the present invention. It is further understood that the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and that the scope of the present invention is accordingly limited by nothing other than the appended claims.
