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Difference between pages "Talk:Battery Pack Configurations/Possible PriusPlus Configurations; Advantages, Disadvantages, and Issues by Ron Gremban" and "Battery Pack Configurations"

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Adapted from ''PriusPlusConfigurations040817rdg.xls''
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There are many ways to implement a [[WikiPedia:battery pack|battery pack]] or traction pack.  In this article we will try to clarify the distinction between simple, parallel, and hybrid implementations.  We realize that the use of the word ''hybrid'' may be confusing, especially when you add ''battery pack'', which might seem to describe the standard traction battery in a hybrid vehicle rather than a particular type of battery pack configuration.
  
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Possible PRIUS+ Configurations; Advantages, Disadvantages, and Issues
+
==Simple==
 +
A '''simple''' pack consists of a '''single series string''' of batteries or cells, this is by far the most common type of battery pack.  If no other modifier is used to describe a battery pack you can usually assume it is a single, simple string.  Ideally the individual batteries are chosen such that a single string of them will satisfy all the requirements of a projects design goals.  However there are instances in which a satisfactory battery is not available to meet all of the demands, or there may be other reasons to use a more complex battery pack configuration.
  
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Ron Gremban, 8/9/04 Updated, 8/17/04; added option 2b
+
==Parallel==
−
+
In the EV world with regards to battery packs '''Parallel''' usually indicated parallel strings of batteries.  They might be disconnectable or hard-wired but probably don't have any advanced electronics between them.  There are special considerations to observe with regards to the interconnects such that one string's total internal resistance is as equal as possible to the other's. Such parallel strings are usually made up of the same type of batteries. They are normally designed to share the load equally and are used to either increase the available power or energy content of the pack.
−
'''General issues'''
 
−
*The PowerThat NiMH "D" cells are currently my first choice for powering the first PRIUS+ prototype.  I have designed the 12-cell modules built from these such that 42 of them can be used with any of the configurations below as follows: 14 series x 3 parallel for #1 or #2 (185/202/252V min/nom/max @ 2.5 useable kWh)    #2 may need 56 modules, 14 series x 4 parallel (same voltages) 21 series x 2 parallel for #3 (277/302/378V min/nom/max @ 4.0 useable kWh) 42 series for #4 or #5 (554/604/756V min/nom/max @ 4.0 u-kWh; 21x2 for charging)
 
−
*Because the oil pump is driven by the ICE, we must ensure that the transaxle is properly oiled during EV-only operations.  All configurations will require a grid charger, along with its controls, cooling air, and removable cord.
 
  
−
==1. Traction battery in parallel with the hybrid battery (suggested by Dan and others)==
+
See also:
−
* '''Advantages''' '''Major win''': Should reduce hybrid battery losses and thereby improve general hybrid performance as well as provide EV range.
+
* Search [http://www.seattleeva.org/maillist/evdl/?search=parallel%20pack&all=1 evdl archives:parallel pack] ~60 matches
−
** '''Disadvantages''' '''Major possible loss''': May disrupt battery ECU's hybrid battery SOC control, thereby reducing the hybrid battery's cycle life. This is especially likely to void the hybrid battery's warranty.
+
* Search [http://www.seattleeva.org/maillist/evdl/?search=parallel%20batter&all=1 evdl archives:parallel batter]-y-ies ~25 matches
−
** '''Issues''' '''Major issue''':  Can the battery ECU be made to properly understand the added SOC after a grid-based charge? Note: grid-charging only the traction battery, connecting it on the far side of the current sensor, and connecting it only during ig-on may solve this issue.
 
−
* '''Advantages''' Win balanced by loss:  Unless it has extra cells, the traction battery can only be discharged to around 56% unless a diode is used to prevent recharge from the THS, then to 40%; in either case increasing its cycle life.
 
−
** '''Disadvantages''' Loss balanced by win: The traction battery can only be discharged to around 56% unless a diode is used to prevent recharge from the THS; then to 40%; thereby reducing its effective capacity to 44% or 60%.  Such a diode, however, will prevent improvement in regenerative braking efficiency and capacity. It is possible, however, that the traction battery's SOC range can be skewed by adding extra cells relative to what the hybrid battery has.  Three extra traction battery cells, for example, will cause 56% hybrid charge to correspond to around 35% traction charge and 40% hybrid charge to correspond to around 20% traction charge.  This ruse, however, might cause the battery ECU to misread the hybrid battery's SOC, thereby operating the hybrid battery beyond its normal SOC limits and reducing its cycle life.
 
−
** '''Issues''' '''Major issue''': Can the hybrid battery ECU and the THS system be made to continue working right, despite the interactions? For example, if SOC is partially determined by integrating current, the ECU's idea of battery size may limit the battery capacity that actually gets used. Expanded battery capacity may remain unused. This will not be a problem if the ECU dynamically determines battery capacity and learns the new capacity.  However, in this case, the original hybrid battery will be overcharged and overdischarged for a while if the additional capacity is removed, until the ECU learns of the once again reduced capacity.
 
−
* '''Advantages''' The hybrid battery will run cooler because the traction battery will be reducing its power loads.
 
−
** '''Disadvantages''' Already handled:  Requires a 168 cell NiMH traction battery.  It may be advisible to divide the traction battery into 12-cell units and parallel each with a hybrid battery tap.
 
−
** '''Issues''' Major issue:  How to control the traction battery's SOC and charge balancing?  Note: the above solution to grid-based charging may work here, too.
 
−
* '''Advantages''' If a diode is not used to prevent the THS from recharging the traction battery with the hybrid battery, then regenerative braking will be more efficient and can last longer during a long descent.  Maybe this effect can be switchable, e.g. turned on when "B" is selected instead of "D".
 
−
** '''Issues''' The traction battery will need to be disconnected from the hybrid battery except during ig-on, to prevent overcharging the hybrid battery and reduction of its cycle life.  Hey, there's a theme here!  But will this be sufficient?  And it might cause problems as the THS notices extraneous current flowing into the hybrid battery.
 
−
* '''Advantages''' The THS' propensity to move the hybrid battery's SOC toward 56%, combined with use of the already-available EV-only mode makes use of the traction battery's charge automatic.
 
−
** '''Issues''' On which side of the hybrid battery's current sensor should the traction battery be connected?  Should its individual modules be connected to the hybrid battery's taps?
 
−
** '''Issues''' The traction battery may need temperature control, due to high peak power requirements.
 
−
 
−
==2. Traction battery replaces the hybrid battery (suggested by Andy Frank)==
 
−
* '''Advantages''' '''Major win''': Cannot reduce the hybrid battery's cycle life, as it is no longer in use.  If fact, the battery can be sold to help finance the modification!
 
−
** '''Disadvantages''' Loss balanced by win:  The value of the hybrid battery's low internal resistance is thrown away (vs. keeping it in parallel).
 
−
** '''Issues''' The traction battery will need temperature control, due to high peak power requirements.  It may, however, fit in the hybrid battery's box, with its existing cooling air and temperature sensors.
 
−
* '''Advantages''' '''Major win''':  A traction battery with a low enough internal resistance should reduce hybrid battery losses and thereby improve hybrid (including regenerative braking) performance (though not as much as with config. #1) as well as provide EV range.
 
−
** '''Disadvantages''' Due to grid-charging to or near 100%, the traction battery will probably not last as long as the hybrid battery would have; however, it will probably last as long as can be expected for a traction battery.
 
−
* '''Advantages''' The larger traction battery does double duty, thereby reducing overall weight, maybe as much as the increase required by its reduced capacity due to limited discharge depth.
 
−
** '''Disadvantages''' Already handled:  Requires a 168 cell NiMH traction battery divisible into 12-cell units to match the hybrid battery taps.
 
  
−
===2a. Toyota's battery ECU remains untouched===
+
==Hybrid==
−
* '''Advantages''' 2a only:  Win balanced by loss:  The traction battery can only be discharged to an average of 56%, thereby increasing its cycle life.
+
The use of the term "hybrid" in relation to a battery pack simply refers to a pack that is a combination of two different types of energy storage devices. It does not refer specifically to a hybrid vehicle, although this section discusses its use in a hybrid vehicle.
−
* '''Advantages''' 2a only:  The THS' propensity to move the hybrid battery's SOC toward 56%, combined with use of the already-available EV-only mode makes use of the traction battery's charge automatic.
 
−
** '''Disadvantages''' 2a only:  Loss balanced by win:  The traction battery can only be discharged to around 56% (a diode cannot be used to prevent recharge from the THS); thereby reducing its effective capacity to 44%.
 
−
** '''Issues''' 2a only:  Major issue:  Will the battery ECU properly control a different battery's SOC and charge balancing? For example, if SOC is partially determined by integrating current, the ECU's idea of battery size may limit the battery capacity that actually gets used. Expanded battery capacity may remain unused.  This will not be a problem if the ECU dynamically determines battery capacity and learns the new capacity.  However, in this case, the battery will be overcharged and overdischarged for a while if the additional capacity is removed and replaced by the original hybrid battery, until the ECU learns of the once again reduced capacity.
 
−
* '''Advantages''' 2a only:  It may be easier to get the battery ECU to properly register and control a different but homogenious battery's SOC and charge balancing than to do so with a combination of the original and added battery.  Also, multiple battery THS interactions are eliminated.
 
−
** '''Disadvantages''' 2a only:  Major issue:  Can the battery ECU be made to properly understand the added SOC after a grid-based charge?
 
  
−
===2b. Toyota's battery ECU is replaced with a custom controller (suggested by Greg Hanssen)===
+
A '''Hybrid''' battery pack is too advanced a setup to be simply called ''parallel''. It would likely be made up of two strings of roughly equivalent voltage, but may be entirely different chemistries or even use caps as one of the strings. There would usually be a DC-DC device between the pack or some other way to manage the flow of power from one string to the other.  Such a Hybrid Battery Pack is used to take advantage of the strong points and mask the weak aspects of the various strings that make up the whole. This is similar to reducing engine size and making up for it with electric motors, as is done with hybrid vehicles.  One might have a high capacity but low power string and a low capacity but high power string and combine them in a manner to utilize both of these strengths and eliminate the weaknesses.
−
* '''Advantages''' 2b only:  Major win:  Custom designed and programmed controller can properly manage a traction/hybrid battery's SOC, and encourage the rest of the THS to make best use of the additional battery capacity and power handling capabilities, while optimizing battery life.
+
 
−
** '''Issues''' 2b only: Need to design and program a replacement battery ECU to accurately gauge SOC, take good care of the battery, and interface with the other ECUs, telling them what they need to know to encourage higher power peaks, both discharge and charge.
+
----
−
+
'''Background Information'''<br>
−
==3. Traction battery provides controlled current into the hybrid battery (suggested by Ron)==
+
In short, a new larger capacity ''(source)'' battery pack and ''[[Battery Chargers|charger]] device'' would float-charge the stock ''(target)'' battery pack at a voltage near the top of its normal operating range, taking care to consider regeneration headroom. A contactor based setup might simply parallel a properly sized source pack with the target on a SOC based duty cycle, additionally a large resistor might be used to limit the current transfer when the source pack is fully  charged and the voltage differential is at its greatest.  Such dump charging is simple and effective but can also be risky if not properly configured.  A DC-DC converter or DC input charger with load following capabilities might also be used to continuously replace the energy removed by the motors while taking care to not overcharge the target battery pack.  It's important to keep the stock battery pack at a voltage which corresponds to a high, yet not full [[SOC]].  The charger would also need to stop discharging the source battery pack when it reaches a particular desired SOC.  Once the source pack is depleted the vehicle should revert to normal operation using only the original battery pack.  A properly configured Hybrid Battery Configuration will exploit the [[State Of Charge Drift]] portion of the vehicles battery management routines in order to accomplish [[State Of Charge Manipulation]].  The use of a [[Battery Tap Emulator]] should not be necessary with these implementations.
−
* '''Advantages''' '''Major win''': The traction battery's SOC and discharge rate can be separated from any hybrid battery and HSC control issues.  Traction battery current can be doled out based on hybrid battery voltage, SOC, and/or other criteria as desired.
+
 
−
** '''Disadvantages''' '''Major cost''': A DC:DC downconverter is needed to control current injection from the traction battery.  A DC motor controller should be able to do this duty.
+
See also:
−
** '''Issues''' '''Major issue''':  Injecting current on the hybrid battery's side of its current sensor may upset the battery ECU's tracking of the hybrid battery's SOC, thereby loosening its control and shortening its cycle life.
+
These Searches may take some time to complete:
−
* '''Advantages''' '''Major win''': Traction battery SOC can be separately monitored and controlled; a full 80% of capacity can be used, or any other amount to optimize EV range vs. battery cycle life cost.
+
* Search [http://www.seattleeva.org/maillist/evdl/?search=hybrid%20pack&all=1 evdl archives:'''hybrid pack'''] ~290 matches
−
** '''Disadvantages''' '''Development cost''': A control system, complete with data inputs (possibly from the CAN bus) and traction battery SOC monitoring, must be created to control the current injection.
+
* Search [http://www.seattleeva.org/maillist/evdl/?search=hybrid%20batter&all=1 evdl archives:'''hybrid batter]-y-ies''' ~102 matches
−
** '''Issues''' '''Major issue''': Injecting current on the far side of the hybrid battery's current sensor may upset the THS' tracking of system currents and voltages, making the system erratic or nonfunctional.
+
** [[EVDL_Maillist:2003./6./317]], [[EVDL_Maillist:2003./6./370]] - Li Ion Series Resistance
−
* '''Advantages''' '''Major win''': A traction battery (e.g. Li-ion) with limited discharge rate and/or different chemistry can be used without harm or inefficiency.
+
** [[EVDL_Maillist:2003./6./896]], [[EVDL_Maillist:2003./6./1180]] - ThunderSky Li & PbA pack
−
** '''Disadvantages''' To avoid requiring a DC:DC upconverter, the minimum traction battery voltage must be higher than 252V, the highest voltage required for hybrid battery charging.
+
** [[EVDL_Maillist:2003./6./1438]] - Using a PFC-50 in a hybrid pack arrangement
−
* '''Advantages''' Limited win: If a battery capable of high discharge rate is used, the current injection can be increased when necessary (until the traction battery is depleted), to improve general hybrid performance.
+
* Search [http://www.seattleeva.org/maillist/evdl/?search=dump%20charge&all=1 evdl archives:'''dump charge'''] ~250 matches
−
** '''Disadvantages''' A charge controller and a DC:DC upconverter or dynamic battery reconfiguration is required to improve the efficiency and duration of regenerative braking by recharging the traction battery, too.
+
 
−
* '''Advantages''' The major issue of current injection into the high voltage bus is replaced by one of this configuration's two major issues.
+
==PHEV Applications==
−
+
 
−
==4. Traction battery provides controlled current into the high voltage (500V) bus (suggested by Ron)==
+
===Conversion topologies===
−
* '''Advantages''' '''Major win''': The traction battery's SOC and discharge rate can be separated from any hybrid battery and HSC control issues. Traction battery current can be doled out based on hybrid battery voltage, SOC, and/or other criteria as desired.
+
At the very least, to convert a non-plug-in HEV into a PHEV, you need a power cord and a battery charger. Beyond that, there are many topologies depending on the battery pack(s) used, and on the Battery Electronic Control Unit (ECU) used.  
−
** '''Disadvantages''' '''Major cost''':  A DC:DC downconverter is needed to control current injection from the traction battery.  A high voltage DC motor controller should be able to do this duty.
+
 
−
** '''Issues''' '''Major issue''':  Depending on how the THS control loop is designed, current injection into the high voltage bus may cause the THS to do the right thing with the extra energy, or not. This must be discovered, and worked around if not what is needed.
+
 
−
* '''Advantages''' '''Major win''': Traction battery SOC can be separately monitored and controlled; a full 80% of capacity can be used, or any other amount to optimize EV range vs. battery cycle life cost.
+
This is a tree of possible PHEV conversion topologies. It also gives examples of conversions that use a given topology.
−
** '''Disadvantages''' '''Development cost''':  A control system, complete with data inputs (possibly from the CAN bus) and traction battery SOC monitoring, must be created to control the current injection.
+
 
−
* '''Advantages''' '''Major win''':  A traction battery (e.g. Li-ion) with limited discharge rate and/or different chemistry can be used without harm or inefficiency.
+
* Stock pack and Battery ECU only
−
** '''Disadvantages''' To avoid requiring a DC:DC upconverter, the minimum traction battery voltage must be higher than 500V.
+
* One or more additional stock packs, in parallel with stock pack
−
* '''Advantages''' '''Major possible win''': If the THS control system is set up in such a way that this configuration works well, it may be possible to use this current injection fool the THS into greatly increasing maximum EV acceleration and maybe even speed, within the limitations of MG2 and MG1.
+
** Using the stock Battery ECU
−
** '''Disadvantages'''  A charge controller and a DC:DC upconverter or dynamic battery reconfiguration is required to improve the efficiency and duration of regenerative braking by recharging the traction battery, too. Note: this reconfiguration may already be available for grid-charging.
+
** Using a custom Battery ECU
−
* '''Advantages''' Limited win:  If a battery capable of high discharge rate is used, the current injection can be increased when necessary (until the traction battery is depleted), to improve general hybrid performance.
+
* New pack only
−
* '''Advantages''' The two major issues of current injection into the hybrid battery are replaced by this configuration's one major issue.
+
** Using the stock Battery ECU (e.g.: [[Prius_PHEV|Original CalCars Method]])
−
+
** Using a custom Battery ECU (e.g.: [[Hybrids-Plus]])
−
==5. Traction battery drives MG2 & MG1 via added controller (suggested by Victor Tikhonov)==
+
* New pack in addition to stock pack (note 1) (e.g.: [[Hymotion]], but which topology?)
−
* '''Advantages''' '''Major win''': The traction battery's SOC and discharge rate can be separated from any hybrid battery and THS control issues.
+
** Two packs connected in parallel (note 2)  
−
** '''Disadvantages''' '''Major cost''': A high voltage (500V), 50kW three-phase AC motor/generator controller is required to drive MG2.
+
*** Using the stock Battery ECU (e.g.: original [[PiPrius]]/[[PriusBlue]])
−
** '''Issues''' '''Major issue''': Can the new controller's regenerative braking be integrated with the brake pedal and friction brakes in the sophisticated user-friendly way it is done by the THS?
+
*** Using a custom Battery ECU
−
* '''Advantages''' '''Major win''':  Traction battery SOC can be separately monitored and controlled; a full 80% of capacity can be used, or any other amount to optimize EV range vs. battery cycle life cost.
+
** Two packs connected through a DC-DC converter (note 3)
−
** '''Disadvantages''' '''Major development cost''': A control system, complete with data inputs (possibly from the CAN bus), traction battery SOC monitoring, and MG2 current and phase monitoring, must be created to control  MG2, including regenerative braking functionality. Much of this may be built into the motor controller, however.
+
*** Using the stock Battery ECU (e.g.: future [[PiPrius]]/[[PriusBlue]])
−
** '''Issues''' '''Major issue''':  Flux-weakening is needed to obtain MG2 torque at its higher RPM ranges.  Can a third-party three-phase AC motor controller be found that can properly handle this flux-weakening chore?
+
*** Using a custom Battery ECU (e.g.: [[EDrive]]/[http://www.energycs.com EnergyCS])
−
* '''Advantages''' '''Major win''':  The replacement traction control system can be used to greatly increase EV acceleration and speed, within the limitations of MG2 and MG1.
+
 
−
** '''Disadvantages''' Major limitation: The traction battery must be able to handle high discharge rates for acceleration and high charge rates for regenerative braking.
+
Notes:
−
** '''Disadvantages''' To avoid requiring a DC:DC upconverter, the minimum traction battery voltage must be 500V.
+
# Called the "Hybrid pack" method elsewhere in this page
 +
# Called the "Contactor" method by the people who use a contactor to selectively connect the two packs in parallel
 +
# Called "PFC method" by the people making the PiPrius conversion, because it uses a product called the "PCF-30"
 +
 
 +
 
 +
Here are some of the advantages and disadvantages of the various topologies:
 +
* The "Stock pack only" topologies are pretty pointless if the range achievable by the stock pack is only a couple of miles.
 +
* The "New Pack Only" topologies do not need to deal with batteries of different chemistries. However, if the same Battery ECU is used, the ECU has to be fooled into operating with the new pack. If the new pack has better characteristics than the stock pack, removing the original pack results in a lighter vehicle for a given range.
 +
* Using the stock ECU is cheaper and somewhat easier, but there may be hassles trying to fool it into working with a different pack. Using a custom Battery ECU avoids all the hassles required to fool the stock ECU, but you have the design effort and cost of a new ECU
 +
* Topologies that use a new pack in addition to the stock pack need to deal with how the two pack are connected (in parallel or through a DC-DC converter). Also, if the new pack has better characteristics than the stock pack, keeping the original pack may be an inefficient use of space and weight.
 +
* See also some useful documents prepared by Ron Gremban on Feb 17, 2006: ''New spreadsheet of projected battery performance in PHEV conversions'', [http://www.forsites.com/CalCars/calcars-phev-batteries18feb06-rdg.xls Excel version], [http://www.forsites.com/CalCars/calcars-phev-batteries18feb06-rdg.pdf pdf version]
 +
 
 +
===Prius===
 +
See also [[Prius PHEV#Hybrid-Pack Method]] for specific conversion examples using this method.
 +
 
 +
See the stock [[Toyota Prius Battery Specs]] and [[Prius PHEV Battery Options#Hybrid-Pack Method]] pages.
 +
 
 +
With regards to the Prius, the term ''parallel'' might be used to describe a pack that uses additional stock batteries which are always connected to the original stock battery.  Though such [[Prius EV Mode Button#Parallel Packs|projects exist]] (using both stock NiMH and PbA chemistries), most do not charge their parallel packs from an AC outlet.
 +
 
 +
Ron's original [[PriusPlus History]] and the [[EDrive]] systems do not use a parallel nor hybrid type pack, rather these implementations replace the stock battery with a simple string. Though they may be capable of switching back to use the stock string, the two packs are not used at the same time.  An advantage of this implementation is that there is no chance of damaging or degrading the stock battery pack which could be removed for weight and space savings or even sold to offset the conversion costs.  If the stock battery is removed, then its replacement must be as robust, in order to prevent failures. The risk can be mitigated by leaving the stock battery in place, so that it can be used should the need arise.
 +
 
 +
The [[Hymotion]] system may ''(I'm speculating)'' be using a Hybrid Pack which is made-up of the stock NiMH string and an additional Li-ion string with some level of management between them.  Such a hybrid setup has also been suggested by a number of EV folks as they have discussed and even implemented such setups for use in pure EV's over the years.  Some benefits of such an implementation may include simplicity of installation because there is no need for a [[Battery Tap Emulator]]: the existing battery and its taps are used.  [[State Of Charge Manipulation]] may still be required using [[State Of Charge Drift]].  Drawbacks might include the need to keep the stock battery which might not be ideal for the tasks of a [[PHEV]] and there may be lighter batteries which could better utilize the space which the stock battery occupies. Though there is a risk of damaging the stock battery, such an implementation should actually reduce the load and number of cycles to which the stock battery is subjected, thus further extending its service life.
 +
 
 +
[[Category:PHEV]]
 +
[[Category:Prius]]

Latest revision as of 09:15, 15 October 2007

There are many ways to implement a battery pack or traction pack. In this article we will try to clarify the distinction between simple, parallel, and hybrid implementations. We realize that the use of the word hybrid may be confusing, especially when you add battery pack, which might seem to describe the standard traction battery in a hybrid vehicle rather than a particular type of battery pack configuration.

Simple

A simple pack consists of a single series string of batteries or cells, this is by far the most common type of battery pack. If no other modifier is used to describe a battery pack you can usually assume it is a single, simple string. Ideally the individual batteries are chosen such that a single string of them will satisfy all the requirements of a projects design goals. However there are instances in which a satisfactory battery is not available to meet all of the demands, or there may be other reasons to use a more complex battery pack configuration.

Parallel

In the EV world with regards to battery packs Parallel usually indicated parallel strings of batteries. They might be disconnectable or hard-wired but probably don't have any advanced electronics between them. There are special considerations to observe with regards to the interconnects such that one string's total internal resistance is as equal as possible to the other's. Such parallel strings are usually made up of the same type of batteries. They are normally designed to share the load equally and are used to either increase the available power or energy content of the pack.

See also:

Hybrid

The use of the term "hybrid" in relation to a battery pack simply refers to a pack that is a combination of two different types of energy storage devices. It does not refer specifically to a hybrid vehicle, although this section discusses its use in a hybrid vehicle.

A Hybrid battery pack is too advanced a setup to be simply called parallel. It would likely be made up of two strings of roughly equivalent voltage, but may be entirely different chemistries or even use caps as one of the strings. There would usually be a DC-DC device between the pack or some other way to manage the flow of power from one string to the other. Such a Hybrid Battery Pack is used to take advantage of the strong points and mask the weak aspects of the various strings that make up the whole. This is similar to reducing engine size and making up for it with electric motors, as is done with hybrid vehicles. One might have a high capacity but low power string and a low capacity but high power string and combine them in a manner to utilize both of these strengths and eliminate the weaknesses.

Background Information
In short, a new larger capacity (source) battery pack and charger device would float-charge the stock (target) battery pack at a voltage near the top of its normal operating range, taking care to consider regeneration headroom. A contactor based setup might simply parallel a properly sized source pack with the target on a SOC based duty cycle, additionally a large resistor might be used to limit the current transfer when the source pack is fully charged and the voltage differential is at its greatest. Such dump charging is simple and effective but can also be risky if not properly configured. A DC-DC converter or DC input charger with load following capabilities might also be used to continuously replace the energy removed by the motors while taking care to not overcharge the target battery pack. It's important to keep the stock battery pack at a voltage which corresponds to a high, yet not full SOC. The charger would also need to stop discharging the source battery pack when it reaches a particular desired SOC. Once the source pack is depleted the vehicle should revert to normal operation using only the original battery pack. A properly configured Hybrid Battery Configuration will exploit the State Of Charge Drift portion of the vehicles battery management routines in order to accomplish State Of Charge Manipulation. The use of a Battery Tap Emulator should not be necessary with these implementations.

See also: These Searches may take some time to complete:

PHEV Applications

Conversion topologies

At the very least, to convert a non-plug-in HEV into a PHEV, you need a power cord and a battery charger. Beyond that, there are many topologies depending on the battery pack(s) used, and on the Battery Electronic Control Unit (ECU) used.


This is a tree of possible PHEV conversion topologies. It also gives examples of conversions that use a given topology.

  • Stock pack and Battery ECU only
  • One or more additional stock packs, in parallel with stock pack
    • Using the stock Battery ECU
    • Using a custom Battery ECU
  • New pack only
  • New pack in addition to stock pack (note 1) (e.g.: Hymotion, but which topology?)
    • Two packs connected in parallel (note 2)
      • Using the stock Battery ECU (e.g.: original PiPrius/PriusBlue)
      • Using a custom Battery ECU
    • Two packs connected through a DC-DC converter (note 3)

Notes:

  1. Called the "Hybrid pack" method elsewhere in this page
  2. Called the "Contactor" method by the people who use a contactor to selectively connect the two packs in parallel
  3. Called "PFC method" by the people making the PiPrius conversion, because it uses a product called the "PCF-30"


Here are some of the advantages and disadvantages of the various topologies:

  • The "Stock pack only" topologies are pretty pointless if the range achievable by the stock pack is only a couple of miles.
  • The "New Pack Only" topologies do not need to deal with batteries of different chemistries. However, if the same Battery ECU is used, the ECU has to be fooled into operating with the new pack. If the new pack has better characteristics than the stock pack, removing the original pack results in a lighter vehicle for a given range.
  • Using the stock ECU is cheaper and somewhat easier, but there may be hassles trying to fool it into working with a different pack. Using a custom Battery ECU avoids all the hassles required to fool the stock ECU, but you have the design effort and cost of a new ECU
  • Topologies that use a new pack in addition to the stock pack need to deal with how the two pack are connected (in parallel or through a DC-DC converter). Also, if the new pack has better characteristics than the stock pack, keeping the original pack may be an inefficient use of space and weight.
  • See also some useful documents prepared by Ron Gremban on Feb 17, 2006: New spreadsheet of projected battery performance in PHEV conversions, Excel version, pdf version

Prius

See also Prius PHEV#Hybrid-Pack Method for specific conversion examples using this method.

See the stock Toyota Prius Battery Specs and Prius PHEV Battery Options#Hybrid-Pack Method pages.

With regards to the Prius, the term parallel might be used to describe a pack that uses additional stock batteries which are always connected to the original stock battery. Though such projects exist (using both stock NiMH and PbA chemistries), most do not charge their parallel packs from an AC outlet.

Ron's original PriusPlus History and the EDrive systems do not use a parallel nor hybrid type pack, rather these implementations replace the stock battery with a simple string. Though they may be capable of switching back to use the stock string, the two packs are not used at the same time. An advantage of this implementation is that there is no chance of damaging or degrading the stock battery pack which could be removed for weight and space savings or even sold to offset the conversion costs. If the stock battery is removed, then its replacement must be as robust, in order to prevent failures. The risk can be mitigated by leaving the stock battery in place, so that it can be used should the need arise.

The Hymotion system may (I'm speculating) be using a Hybrid Pack which is made-up of the stock NiMH string and an additional Li-ion string with some level of management between them. Such a hybrid setup has also been suggested by a number of EV folks as they have discussed and even implemented such setups for use in pure EV's over the years. Some benefits of such an implementation may include simplicity of installation because there is no need for a Battery Tap Emulator: the existing battery and its taps are used. State Of Charge Manipulation may still be required using State Of Charge Drift. Drawbacks might include the need to keep the stock battery which might not be ideal for the tasks of a PHEV and there may be lighter batteries which could better utilize the space which the stock battery occupies. Though there is a risk of damaging the stock battery, such an implementation should actually reduce the load and number of cycles to which the stock battery is subjected, thus further extending its service life.

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