Battery charger control system

• US 5,844,399 A
• Filed: 07/26/1996
• Issued: 12/01/1998
• Est. Priority Date: 07/26/1996
• Status: Expired due to Fees

• Current Assignee: University of Toledo
• Original Assignee: University of Toledo
• Inventors: Stuart, Thomas A.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): SHIN, KYUNG E
• Application Number:
  US08/687,810
• Time in Patent Office: 858 Days
• Field of Search: 320/30, 320/31, 320/35, 320/39, 320/50, 320/48, 320/2, 320/27, 320/28, 320/29, 320/9, 320/10, 320/11, 307/64, 323/222, 323/224, 323/282-287, 323/271-272, 323/907
• US Class Current: 323/282
• CPC Class Codes: G05F 1/67 to the maximum power available from a generator, e.g. from solar cell
• CPC Class Codes: H01M 10/44 Methods for charging or discharging circuits for charging H02J7/00
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A battery charger control system and method for maximizing output power to a battery. This is achieved by ensuring operation at either the maximum allowable input current or the thermal limit imposed by the battery charger using an on-line controller. In the invention, the thermal limit is determined by the junction temperatures of the two main IGBT'"'"'s. Because direct measurement of these temperatures is impractical, they must be calculated by a computer algorithm that uses various on-line measurements. Test results for a 8 kW battery charger indicate reduction in the bulk charging time from conventional battery chargers of about 26% when charging a set of NiFe batteries.

Claims

1. A maximum power transfer method for using a battery charger to charge a battery, the method comprising the steps of:

(1) measuring an input current of the battery charger;

(2) determining whether the input current is greater than a maximum input current, and if so, decreasing a reference battery current of the battery charger and returning to step (1);

(3) measuring an input and output voltage of a boost stage of the battery charger, a battery voltage, a battery current and a heat sink temperature of the battery charger;

(4) determining a junction temperature of the boost stage;

(5) determining whether the junction temperature of the boost stage is greater than a maximum junction temperature of the boost stage, and if so, decreasing the reference battery current of the battery charger and returning to step (1);

(6) determining a junction temperature of a buck stage of the battery charger;

(7) determining whether the junction temperature of the buck stage is greater than a maximum junction temperature of the buck stage, and if so, decreasing the reference battery current of the battery charger and returning to step (1);

(8) increasing the reference battery current; and

(9) returning to step (1).

2. The method according to claim 1, wherein the junction temperature of the boost stage is determined by on-line measurements of conduction and switching losses in the boost stage.

3. The method according to claim 1, wherein the junction temperature of the buck stage is determined by on-line measurements of conduction and switching losses in the buck stage.

4. A battery charger for maximizing charging current to a battery, comprising:

a filter/rectifier for converting an input current from alternating current to direct current for said batter charger;

a boost stage connected to said filter/rectifier for providing a power factor correction circuit of said battery charger;

a buck stage connected to said boost stage for providing output current control of said battery charger; and

a controller connected to at least one of said boost and buck stages for determining at least one of a junction temperature of said boost and buck stages of said battery charger.

5. The battery charger according to claim 4, wherein said boost stage comprises an inductor connected to said current source, a semiconductor switching device connected to the inductor, a diode connected to the inductor and a capacitor connected across the semiconductor switching device and to the diode.

6. The battery charger according to claim 4, wherein, said buck stage comprises an semiconductor switching device connected to said boost stage, a diode connected to the semiconductor switching device, a inductor connected to the semiconductor switching device and a capacitor connected across the diode and the inductor.

7. The battery charger according to claim 4, wherein the junction temperatures of said boost and buck stages are determined by measuring at least one of the input current to said battery charger, an input and output voltage of said boost stage, a battery voltage, an average battery current and a heat sink temperature of said battery charger.

8. A method for controlling output power of a battery charger, comprising the steps of:

(1) determining operating conditions of at least one stage of a battery charger be determining whether a junction temperature of at least one of a boost stage and a buck stage of the battery charger is greater than a maximum junction temperature of a respective boost stage and buck stage; and

(2) controlling the output power of the battery charger by maximizing an input current based on the operating conditions determined in step (1).

9. The method of claim 8, wherein the operating conditions of step (1) comprise a junction temperature of a boost stage and a junction temperature of a buck stage of the battery charger.

10. The method of claim 9, wherein the junction temperatures are determined by on-line measurements of an input and output voltage of the boost stage and a battery voltage, a battery current and a heat sink temperature of the battery charger.

11. The method of claim 8, wherein the output power is maximized by determining whether the input current is greater than a maximum input current, and if so, decreasing a reference battery current of the battery charger.