DISTRIBUTED BATTERY POWER ELECTRONICS ARCHITECTURE AND CONTROL

• US 20140125284A1
• Filed: 10/30/2013
• Published: 05/08/2014
• Est. Priority Date: 10/30/2012
• Status: Active Grant

• Current Assignee: Board of Trustees of The University of Alabama (University of Alabama System)
• Original Assignee: Board of Trustees of The University of Alabama (University of Alabama System)
• Inventors: Qahouq, Jaber Abu
• Granted Patent: US 9,368,991 B2
• Time in Patent Office: Days
• US Class Current: 320/118
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/00 Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
• CPC Class Codes: H02J 7/0018 using separate charge circuits
• CPC Class Codes: H02J 7/0032 disconnection of loads if battery is not under charge, e.g. in vehicle if engine is not running

Abstract

A battery pack having a plurality of battery pack modules, wherein each battery pack module includes a battery cell and a power converter. The power converters of the plurality of battery pack modules are connected in series to form a string of N battery pack modules such that the voltage across the N battery pack modules defines the output voltage of the battery pack. A controller regulates the output voltage of each battery cell or module power converter and the output voltage of the battery pack by independently controlling each battery cell module in accordance with variables such as state-of-charge (SOC), state-of-health (SOH) and temperature, capacity, and temperature of each individual battery cell module. The power converter may be used to measure impedance of the battery pack by adding a sinusoidal perturbation signal to a reference voltage of the cell battery pack module.

Claims

1. A battery pack, comprising:

a plurality of battery pack modules, each battery pack module comprising a battery cell and a power converter; and

a controller that regulates an output voltage of the battery pack,

wherein a power converter of each of the plurality of battery pack modules are connected in series to form a string of N battery pack modules, wherein each battery pack module is independently controlled, and wherein the voltage across the N battery pack modules defines the output voltage of the battery pack.

2. The battery pack of claim 1, wherein a battery pack voltage reference value is determined by the controller in a constant voltage mode, wherein an initial voltage reference value for each battery pack module is determined by dividing the battery pack voltage reference value by a number of active battery pack modules in the battery pack, and wherein the initial voltage reference value for each battery pack module is used to regulate an output voltage of a respective battery pack module.

3. The battery pack of claim 2, wherein a voltage loop multiplier is specified by the controller for each battery pack module, and wherein the voltage loop multiplier is used to adjust a state of charge (SOC) of each battery pack module.

4. The battery pack of claim 3, wherein the voltage loop multiplier is determined by comparing the SOC of each battery pack module to a reference SOC value.

5. The battery pack of claim 4, wherein the reference SOC value is determined by adding the SOC of each battery pack module and dividing a total by the number of active battery pack modules.

6. The battery pack of claim 4, wherein a SOC multiplier is specified for each battery pack module to alter the charge rate or discharge rate of a respective battery pack module.

7. The battery pack of claim 2, wherein an estimate of an impedance of each of the battery pack modules is performed by add a sinusoidal signal to the initial voltage reference value for each battery pack module.

8. The battery pack of claim 7, wherein each sinusoidal signal applied to the initial voltage reference value for each battery pack module is shifted to cancel the sinusoidal signal in the output voltage.

9. The battery pack of claim 7, wherein the impedance is used by the controller to determine a state of charge (SOC) and/or state of health (SOH) of each cell and battery pack module.

10. The battery pack of claim 1, wherein a battery pack current reference value is determined by the controller in a constant current mode, wherein an initial current reference value for each battery pack module is determined by dividing the battery pack current reference value by a number of active battery pack modules in the battery pack, and wherein the initial current reference value for each battery pack module is used to regulate an output current of a respective battery pack module.

11. The battery pack of claim 10, wherein a current loop multiplier is specified by the controller for each battery pack module, and wherein the current loop multiplier is used to adjust a state of charge (SOC) of each battery pack module.

12. The battery pack of claim 11, wherein the current loop multiplier is determined by comparing the SOC of each battery pack module to a reference SOC value.

13. The battery pack of claim 12, wherein the reference SOC value is determined by adding the SOC of each battery pack module and dividing a total by the number of active battery pack modules.

14. The battery pack of claim 12, wherein a SOC multiplier is specified for each battery pack module to alter the charge rate or discharge rate of a respective battery pack module.

15. The battery pack of claim 1, wherein the controller operates in a constant current charging mode until a battery cell voltage reaches a maximum, and wherein the controller thereafter operates in a constant voltage charging mode until a battery cell current falls below a minimum value.

16. The battery pack of claim 1, wherein the power converter of each of the battery pack modules has a DC duty cycle value (D_dc) to produce a corresponding DC battery voltage V_battery—

_dc and DC battery current I<sub>battery—

dc</sub>, wherein when an impedance measurement mode of the power convert is triggered, a sinusoidal duty cycle perturbation signal (d_ac) at a frequency of interest (f_p) with a peak amplitude of D_ac is added to D_dc.

17. The battery pack of claim 16, wherein the perturbation frequency (f_p) is significantly lower than the switching frequency (f_sw) of the power converter to generate sinusoidal ripples superimposed over the power converter DC output voltage V_o—

_dc, DC battery voltage V<sub>battery—

dc</sub> and DC battery current I<sub>battery—

dc</sub>.

18. The battery pack of claim 16, wherein a peak-to-peak value of the battery voltage (V_battery-pp) and the battery current (I_battery-pp) is measured to determine a battery impedance magnitude value at the given perturbation frequency (f_p).

19. The battery pack of claim 18, wherein if there is a phase shift between the battery voltage and current and/or phase information, the following relationship is used to determine the phase of the battery impedance at f_p:

∠

z_battery=φ

_v−

φ

_i

wherein φ

_v is a phase of the battery voltage and φ

_i is a phase of the battery current.

20. A method of controlling a battery pack using a controller that regulates an output voltage of the battery pack, comprising:

determining a battery pack voltage reference value by the controller in a constant voltage mode;

determining an initial voltage reference value for each battery pack module by dividing the battery pack voltage reference value by a number of active battery pack modules in the battery pack; and

using the initial voltage reference value for each battery pack module to regulate an output voltage of a respective battery pack module.

21. The method of claim 20, further comprising:

specifying a voltage loop multiplier by the controller for each battery pack module; and

applying the voltage loop multiplier to adjust a state of charge (SOC) of each battery pack module.

22. The method of claim 21, further comprising:

determining the voltage loop multiplier by comparing the SOC of each battery pack module to a reference SOC value; and

determining the reference SOC value by adding the SOC of each battery pack module and dividing a total by the number of active battery pack modules.

23. The method of claim 20, further comprising:

estimating an impedance of each of the battery pack modules by adding a sinusoidal signal to the initial voltage reference value for each battery pack module; and

applying the sinusoidal signal to shift the initial voltage reference value for each battery pack module to cancel the sinusoidal signal in the output voltage.

24. The method of claim 20, further comprising;

operating a power converter at a DC duty cycle value (D_dc) to produce a corresponding DC battery voltage V<sub>battery—

dc</sub> and DC battery current I<sub>battery—

dc</sub>;

triggering an impedance measurement mode of the power convert by adding a sinusoidal duty cycle perturbation signal (d_ac) at a frequency of interest (f_p) with a peak amplitude of D_ac to D_dc; and

measuring a peak-to-peak value of the battery voltage (V_battery-pp) and the battery current (I_battery-pp) to determine a battery impedance magnitude value at the given perturbation frequency (f_p).

25. A method of controlling a battery pack using a controller that regulates an output voltage of the battery pack, comprising:

determining a battery pack current reference value is determined by the controller in a constant current mode;

determining an initial current reference value for each battery pack module by dividing the battery pack current reference value by a number of active battery pack modules in the battery pack; and

using the initial current reference value for each battery pack module to regulate an output current of a respective battery pack module.

26. The method of claim 25, further comprising:

specifying a current loop multiplier by the controller for each battery pack module; and

using the current loop multiplier to adjust a state of charge (SOC) of each battery pack module.

27. The method of claim 25, further comprising:

operating the controller in a constant current charging mode until a battery cell voltage reaches a maximum; and

operating the controller in a constant voltage charging mode until a battery cell current falls below a minimum value.

28. The method of claim 25, further comprising;

operating a power converter at a DC duty cycle value (D_dc) to produce a corresponding DC battery voltage V<sub>battery—

dc</sub> and DC battery current I<sub>battery—

dc</sub>;

triggering an impedance measurement mode of the power convert by adding a sinusoidal duty cycle perturbation signal (d_ac) at a frequency of interest (f_p) with a peak amplitude of D_ac to D_dc; and

measuring a peak-to-peak value of the battery voltage (V_battery-pp) and the battery current (I_battery-pp) to determine a battery impedance magnitude value at the given perturbation frequency (f_p).