Multicell battery pack bilateral power distribution unit with individual cell monitoring and control

• US 5,656,915 A
• Filed: 08/28/1995
• Issued: 08/12/1997
• Est. Priority Date: 08/28/1995
• Status: Expired due to Term

• Current Assignee: Enersys Energy Products, Inc. (EnerSys)
• Original Assignee: Stephen S. Eaves
• Inventors: Eaves, Stephen S.
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/519,662
• Time in Patent Office: 715 Days
• Field of Search: 320/5, 320/6, 320/7, 320/15, 320/16, 320/17, 320/18, 320/39, 320/48
• US Class Current: 320/118
• CPC Class Codes: H01M 10/482 for several batteries or cells simultaneously or sequentially
• CPC Class Codes: H02J 7/0014 Circuits for equalisation of charge between batteries
• CPC Class Codes: H02J 7/0024 Parallel/serial switching of connection of batteries to charge or load circuit
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A power distribution unit (PDU) for series connected multicell battery packs which uses a common hardware platform for both charging and providing power to an external load. Using switching circuitry (2), and tap points (5a,5b,5c,5d,5e) individual access to cells (4a,4b,4c,4d) or groups of series connected cells is accomplished. Under control of microcontroller circuitry (1), series connected cell groups of varying sizes are selected and prioritized for connection to a common power bus (29),(30) at real-time speeds. The PDU uses these groups to maintain balance over cells with varying characteristics, adapt to varying charge sources and to produce a regulated output voltage during discharge.

Claims

1. In a multicell battery pack comprising a plurality of series connected cells, a power distribution unit for providing regulated, bi-directional transfer of energy to and from said pack or a selected portion of the pack comprising:

(a) a plurality of electrical tap points located at the end poles of the pack and at the junction between sets of one or more series connected cells within said pack, whereby any two consecutive tap points present the positive and negative poles of the cell set in-between, and where any two non-consecutive tap points present the positive and negative pole of a larger group produced by the series connection of all the cell sets between said non-consecutive tap points;

(b) at least two bus conductors for the transfer of energy into or out of any selected group of cell sets within said pack;

(c) individually controlled switching means for allowing current flow in at least one direction from any tap point to at least one bus conductor and individually controlled switching means for allowing current flow in at least one direction from the same tap point to at least one other bus conductor;

(d) controller means for executing pack control algorithm means for selecting the most suitable group of cell sets for regulating a preset output voltage to an external load and the most suitable group of cell sets for regulating the receipt of energy from an external source, and where said controller means includes the functionality of accessing and actuating said individually controlled switching means, and the input and output of analog and digital signals related to the control of said power distribution unit;

(e) sensing means for measuring a value indicative of the electrical current flow into or out of each cell set contained in said pack and supplying the measurement to said controller;

(f) sensing means with at least enough sensor connection points to measure a value indicative of the voltage across the poles of each cell set within said pack and at most enough sensor connection points to measure a value indicative of the voltage across the poles of each individual cell within said pack, and supplying the measurement to said controller;

(g) sensing means for measuring a value indicative of the voltage across the output terminals of said power distribution unit and supplying the measurement to said controller.

2. The power distribution unit of claim 1 where said controller means manages the internal transfer of energy from a first selected group of cell sets to a second selected group of cell sets by:

(a) accessing said switching means to connect the negative pole of the first group to one of the bus conductors and to connect the positive pole of said first group to one other bus conductor, whereby an intermediate energy storage device means which resides across the two bus conductors charges, at least in part, to the terminal voltage of said first group;

(b) disconnecting said first group from said two bus conductors;

(c) connecting the second group, which has been selected by said pack control algorithm means to have a terminal voltage less than the voltage across said storage device, to said two bus conductors, whereby electrical current flows from said storage device into said second group.

3. The power distribution unit of claim 1 where said controller means regulates a preset output voltage to an external load by employing a selection algorithm means to continuously select groups of cell sets of varying size and polarity and connect said groups of cell sets to said at least two bus conductors using said switching means, whereby a waveform is produced which approximates a sinewave of predetermined amplitude and frequency across said at least two bus conductors.

4. The power distribution unit of claim 1 where said controller means regulates a preset output voltage to an external load by:

(a) employing a selection algorithm means which selects a first group of cell sets that has a terminal voltage greater than the preset output voltage;

(b) employing a selection algorithm means which selects a second group of cell sets that has a terminal voltage less than said preset output voltage where said second group may also be a null group with a terminal voltage of approximately zero;

(c) accessing said switching means to successively connect said first group and said second group across said at least two bus conductors with a connection time ratio between said first group and said second group suitable to produce an average voltage output fore said power distribution unit which closely approximates said preset output voltage.

5. The power distribution unit of claim 1 where said controller means regulates the receipt of energy from an external source by:

(a) using the power distribution unit output terminal voltage sensing means to sample at least twice for a single preset charge pulse period, the voltage across the distribution unit output terminals;

(b) analyzing the voltage samples using mathematical means to produce a rate of change of the absolute value of the output terminal voltage and a predicted value of said output terminal voltage as it will exist after said preset charge pulse period has expired;

(c) if the absolute value of said output terminal voltage is increasing, accessing said switching means to connect a group of cell sets which have a series voltage less than or equal to the last sample taken of said output terminal voltage whereby electrical current will flow through said bus conductors to charge said group of cell sets;

(d) if the absolute value of said output terminal voltage is decreasing, accessing said switching means to connect a group of cell sets with a series voltage less than or equal to said predicted value of said output terminal voltage whereby for the duration of said charge pulse period electrical current will remain flowing through said bus conductors to charge said group of cell sets.

6. The power distribution unit of claim 1 where said pack control algorithm means for selecting the most suitable group of cell sets for regulating a desired output voltage to an external load and the most suitable group of cell sets for regulating the receipt of energy from an external source uses the operating temperature of said individually controlled switching means as a factor in selecting said most suitable group of cell sets.

7. The power distribution unit of claim 1 where said pack control algorithm means for selecting the most suitable group of cell sets for regulating a preset output voltage to an external load and the most suitable group of cell sets for regulating the receipt of energy from an external source includes factors that optimize the following:

energy transfer efficiency, balance of state of charge between said cell sets and maintaining the reliability of said power distribution unit.

8. The power distribution unit of claim 1 where a plurality of said series connected cells have been replaced by high density capacitors.

9. An application of the power distribution unit of claim 1 where a series connection means is used to configure an external energy source and said power distribution in series, whereby a voltage is produced across an external load which represents the algebraic summation of the output voltages of said external energy source and said power distribution unit, and where the power distribution unit controller means employs a selection algorithm means which selects groups of cell sets to control said algebraic summation to approximate a preset output voltage across said external load.

10. In a power distribution unit comprised of a series connected multicell battery pack, a controller means for executing internal control algorithm means and an electronic switching network means for establishing a path for bi-directional energy distribution between an external device and said pack or selected portions of said pack, a method for managing said bi-directional energy distribution comprising the steps of:

(a) dividing said pack into fixed sets of one or more series connected cells, where said cell sets may be accessed individually to add or remove energy, or accessed in contiguous groups ranging in size from a null cell set to a size equal to the total number of cell sets in said pack;

(b) selecting one combination of contiguous cell sets, hereafter referred to as a charge priority group, for at least one possible group size, which is most suitable to receive additional energy based upon charge group priority factors which include the optimization of the following;

balance of state of charge between said cell sets, charging speed, pack capacity, charging efficiency, cell life and said power distribution unit reliability;

(c) storing in said controller'"'"'s memory the charge priority group information necessary to actuate said electronic switching network means to establish an energy path between an external energy source and said charge priority group;

(d) continuously measuring the voltage level of said external energy source during periods where said power distribution unit is charging said pack, and selecting a group size which is most suited to be connected to an external energy source based upon charge group size factors which include the optimization of;

balance of state of charge between said cell sets, charging efficiency, cell life, said power distribution unit reliability;

(e) retrieving said charge priority group information from said controller memory and using the information to actuate said electronic switching network means whereby regulated energy flows from said external energy source to said charge priority group;

(f) selecting one combination of contiguous cell sets, hereafter referred to as a discharge priority group, for at least one possible group size, which is most suitable to discharge energy based upon discharge group priority factors which include the optimization of the following;

balance of state of charge between said cell sets, pack energy capacity, discharge efficiency, cell life and said power distribution unit reliability;

(g) storing in said controller'"'"'s memory the discharge priority group information necessary to actuate said electronic switching network means to establish an energy path between an external load and said discharge priority group;

(h) continuously monitoring said external load requirements during discharge, and selecting a group size which is most suited to provide regulated energy to said external load based upon discharge group size factors which include the optimization of the following;

balance of state of charge between said cell sets, discharge efficiency, said distribution unit reliability;

(I) retrieving said discharge priority group information from said controller memory and using the information to actuate said electronic switching means whereby regulated energy flows from said discharge priority group to said external load;

(j) continuously monitoring the state of charge of cells within each cell set and disabling any cell set which contains cells outside preset state of charge limits from being selected as a component in any priority group;

(k) reducing the maximum possible priority group size as cell sets become disabled.

11. The method of claim 10 where group sizes are selected to maintain a distribution unit output voltage to an external load which approximates a sinewave.

12. The method of claim 10 where said discharge group size factors include selecting group sizes which are common denominators of said maximum possible priority group size in order to reduce usage overlap between groups of cell sets, thus improving energy distribution balance between said group of cell sets.

13. The method of claim 10 where group sizes are selected to maintain a preset power distribution unit output voltage by steps comprising:

(a) assigning a discharge group weighting value to each said discharge priority group using mathematical weighting means based upon said discharge group priority factors;

(a) selecting a first discharge priority group which satisfies the requirements of both having the highest said discharge group weighting value and having a group terminal voltage which is closest without exceeding the preset output voltage;

(a) selecting a second discharge priority group which satisfies the requirements of both having the highest said discharge weighting value and having a group terminal voltage which is closest without being less than said preset output voltage;

(c) actuating said electronic switching means to successively connect said first group and said second group to said external load with a connection time ratio between said first group and said second group suitable to produce an average voltage which approximates said desired output voltage.

14. The method of claim 10 where said charge group priority factors and said discharge group priority factors include using historical information of past charge and discharge cycles of said cell sets.

15. The power distribution unit of claim 10 where said controller means regulates the receipt of energy from an external source by steps comprising:

(a) sampling at least twice for a single preset charge pulse period, the voltage of said external energy source;

(b) analyzing the samples using mathematical means to produce a rate of change of the absolute value of said external energy source voltage and a predicted value of said external energy source voltage as it will exist after said preset charge pulse period has expired;

(c) if the absolute value of said bus voltage is increasing, accessing said switching means to connect a group of cell sets which have a terminal voltage less than or equal to the last sample taken of said external energy source voltage whereby electrical current will flow from said external energy source to charge said group of cell sets;

(d) if the absolute value of said external energy source voltage is decreasing, accessing said switching means to connect a group of cell sets with a terminal voltage less than or equal to said predicted value of said external energy source voltage whereby during said charge pulse period electrical current will remain flowing from said external energy source to charge said group of cell sets.

16. The power distribution unit of claim 10 where said electronic switching network means includes the use of power semiconductors which distribute the majority of the distribution unit energy, and where the body of said power semiconductors are attached using thermally conductive attachment means to a thermally dissipative portion of a plurality of battery cells within said pack, whereby a conventional heatsink is not required for said power semiconductors and a reduction in space requirements for said electronic switching means is obtained.