Current-limited system for capacitive load powering

• US 5,642,027 A
• Filed: 02/06/1995
• Issued: 06/24/1997
• Est. Priority Date: 01/07/1992
• Status: Expired due to Fees

• Current Assignee: John A. Windes, Samuel W. Stevens
• Original Assignee: John A. Windes, Samuel W. Stevens
• Inventors: Stevens, Samuel W., Windes, John A.
• Primary Examiner(s): Wong, Peter S.
• Assistant Examiner(s): Law, Patrick B.
• Application Number:
  US08/383,988
• Time in Patent Office: 869 Days
• Field of Search: 320/1, 320/35, 323/282, 323/283, 323/901, 307/48
• US Class Current: 320/166
• CPC Class Codes: H02J 7/34 Parallel operation in networks using both storage and other dc sources, e.g. providing buffering H02J7/14 takes precedence
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators

Abstract

In a capacitor-based energy storage system, in which the capacitor charging voltage is on the same order of magnitude as the system output voltage, the time between recharges for a given energy release rate is extended by producing an intermediate regulated capacitor output of a voltage having a lower order of magnitude and then stepping that voltage back up to the system output voltage through the use of an inverter. Regulation of the capacitor output voltage may be achieved through the use of a capacitor-voltage-dependent variable-duty-cycle switching transistor and an averaging network, which together maintain a level inverter input voltage independently of the capacitor voltage. The cycle control is powered by a rechargeable battery which recharges from the inverter input but cannot drive the inverter, and current and temperature sensing means are provided to control the transistor so as to limit the current draw through the transistor and to prevent battery overheating during operation.

Claims

1. A capacitor-based energy storage and release system comprising:

a) capacitive energy storage apparatus having a capacitor voltage thereacross when charged;

b) a voltage regulator arranged to produce an output at an output voltage which is a small fraction of said capacitor voltage as long as said capacitor voltage is higher than said output voltage;

c) a switch for selectably connecting said energy storage means to a source of relatively high charging voltage, and to the input of said voltage regulator means; and

d) an inverter connected to said voltage regulator and arranged to convert said output voltage to a substantially higher load operating voltage;

e) said voltage regulator including;

i) a transistor, said capacitive energy storage apparatus being connected to said inverter through the emitter-collector circuit of said transistor, and said transistor being arranged to be turned on and off in accordance with a variable duty cycle to produce a square-wave output voltage peaking at said capacitor voltage;

ii) control circuitry connected to said transistor and arranged to vary said duty cycle so as to produce a current-limited transistor output at a substantially constant average voltage, regardless of variations in said capacitor voltage and the current requirements of said load, said control circuitry including

1) a pulse width modulator operatively connected to said inverter and arranged to put out a pulse train whose duty cycle is variable in such a way as to maintain a substantially constant average voltage on said inverter during variations in the voltage of said energy storage apparatus;

2) a gate driver connected to said transistor and said pulse width modulator and arranged to switch said transistor on and off in synchronism with said pulse train; and

3) a current sensor connected to said transistor and to said control circuitry and arranged to substantially limit the current drawn through said transistor to a predetermined value;

iii) a battery for providing power to said pulse width modulator and gate driver; and

iv) a diode arranged to allow said battery to be charged from the input to said inverter but to prevent it from driving said inverter;

v) said pulse width modulator having applied thereto a signal which is a function of the voltage at said inverter and the average voltage at the output of said transistor, said duty cycle of said pulse train being so varied by a combination of said voltages as to maintain said combination of voltages substantially constant in spite of substantial variations in the voltage of said energy storage apparatus.

2. A capacitor-based energy storage and release system comprising:

a) capacitive energy storage apparatus having a capacitor voltage thereacross when charged;

b) a voltage regulator arranged to produce an output at an output voltage which is a small fraction of said capacitor voltage as long as said capacitor voltage is higher than said output voltage;

c) a switch for selectably connecting said energy storage means to a source of relatively high charging voltage, and to the input of said voltage regulator means; and

d) an inverter connected to said voltage regulator and arranged to convert said output voltage to a substantially higher load operating voltage;

e) said voltage regulator including;

i) a transistor, said capacitive energy storage apparatus being connected to said inverter through the emitter-collector circuit of said transistor, and said transistor being arranged to be turned on and off in accordance with a variable duty cycle to produce a square-wave output voltage peaking at said capacitor voltage;

ii) control circuitry connected to said transistor and arranged to vary said duty cycle so as to produce a current-limited transistor output at a substantially constant average voltage, regardless of variations in said capacitor voltage and the current requirements of said load, said control circuitry including

1) a pulse width modulator operatively connected to said inverter and arranged to put out a pulse train whose duty cycle is variable in such a way as to maintain a substantially constant average voltage on said inverter during variations in the voltage of said energy storage apparatus;

2) a gate driver connected to said transistor and said pulse width modulator and arranged to switch said transistor on and off in synchronism with said pulse train; and

3) a current sensor connected to said transistor and to said control circuitry and arranged to substantially limit the current drawn through said transistor to a predetermined value;

iii) a battery for providing power to said pulse width modulator and gate driver; and

iv) a diode arranged to allow said battery to be charged from the input to said inverter but to prevent it from driving said inverter.

3. The apparatus of claim 2, in which said voltage regulator further includes:

v) a temperature sensor for producing a signal representative of the temperature of said battery, said signal being connected to said control circuitry so as to maintain said transistor in a disconnect mode when the temperature of said battery exceeds a predetermined limit.