Uninterruptible power supply (UPS) and method

• US 5,483,463 A
• Filed: 07/30/1993
• Issued: 01/09/1996
• Est. Priority Date: 07/30/1993
• Status: Expired due to Term

• Current Assignee: Controlled Power Company
• Original Assignee: Controlled Power Company
• Inventors: Qin, Yu, Du, Shanshan
• Primary Examiner(s): Shoop, Jr., William M.
• Assistant Examiner(s): GANJIAN, PETER
• Application Number:
  US08/100,111
• Time in Patent Office: 893 Days
• Field of Search: 395/750, 395/900, 307/64-66, 364/492, 364/493
• US Class Current: 700/297
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: Y10S 706/90 Fuzzy logic

Abstract

A UPS having a ferroresonant transformer is selectively switched from AC line voltage to an inverter by a control method and apparatus using fuzzy logic to select an optimum switching point. The control apparatus and method senses output load current, output voltage and input voltage. Output current is used to calculate output load as a percentage of full load. First membership functions relating to percent load, second membership functions relating to output voltage, third membership functions relating to input voltage switching points, and rules using percent load membership and output voltage membership as antecedents and values of input voltage switching points as consquents as determined by regulation characteristics of the ferroresonant transformer, are used to execute a fuzzy inference and generate dynamic input voltage switching points for comparison with line input voltage to control switching of the UPS between line and inverter sources.

Claims

1. An uninterruptible power supply comprising:

a voltage regulating transformer having predetermined voltage regulation characteristics as a function of load,

first input means for coupling a primary AC voltage source to said transformer,

an inverter circuit adapted to be energized by a reserve DC voltage source to provide a secondary AC voltage source,

second input means for coupling said secondary AC voltage source to said transformer,

output means for supplying a regulated output voltage from said regulating transformer to a variable load,

first sensing means for developing a first monitoring signal which varies with voltage at said primary source,

second sensing means for developing a second monitoring signal which varies with at least one electrical parameter as a function of load variations,

input switching means for selectively switching between said first input means and said second input means to supply AC voltage to said transformer,

controller means responsive to said second monitoring signal for determining input voltage switching points which vary on a continuous, non-stepwise basis as a function of load variations, and

a comparator for comparing said continuously varying, non-stepwise switching points to said first monitoring signal to activate said input switching means, and wherein

said controller means comprises means responsive to said second monitoring signal to compute percent load on a dynamic continuous basis and

fuzzy inference apparatus means for executing a fuzzy inference operation using at least first membership functions relating to percent load, second membership functions relating to input voltage switching points, and rules using at least load memberships as antecedents and grades of input voltage switching points as consequences as determined by said regulation characteristics of said transformer to generate said switching points on a continuous, non-stepwise basis.

2. The UPS set forth in claim 1 wherein said transformer is a ferroresonant transformer.

3. The UPS set forth in claim 1 wherein said one load parameter is output current.

4. The UPS set forth in claim 3 further comprising third sensing means for developing a third monitoring signal which varies as a function of output voltage at said load and said means for executing a fuzzy inference operation uses third membership functions relating to output voltage as antecedents and rules using percent load membership and output voltage membership as consequents to generate said input voltage switching points.

5. In an uninterruptible power supply of the type having:

a ferroresonant voltage regulating transformer having predetermined voltage regulating characteristics as a function of load,

first input means for coupling a primary AC voltage source to said transformer,

an inverter circuit adapted to be energized by a reserve DC voltage source to provide a secondary AC voltage source,

second input means for coupling said secondary source to said regulating transformer,

output means for supplying a regulated output voltage from said transformer to a variable load,

first sensing means for developing a first monitoring signal which varies with voltage at said primary source,

second sensing means for developing a second monitoring signal which varies with at least one electrical parameter at said load,

input switching means for selectively switching between said first input means and said second input means to supply AC voltage to said regulating transformer, and

controller means responsive to said first and said second monitoring signals to actuate said switching means as a function of both said one load parameter and voltage at said primary source;

the improvement wherein said controller means dynamically generates input voltage switching points on a continuous non-stepwise basis as a function of percent load and comprises

means responsive to said second monitoring signal to compute percent load and

fuzzy interference apparatus means for executing a fuzzy inference operation using membership functions relating to percent load, membership functions relating to input voltage switching points, and rules using at least percent load memberships and grades of input voltage switching points as determined by said regulation characteristics of said transformer to dynamically generate said switching points on a continuous non-stepwise basis for comparison with said primary voltage to control switching of said UPS between said primary and said secondary sources as a function of load and said primary voltage.

6. The improvement set forth in claim 5 further comprising third means for developing a third monitoring signal which varies as a function of output voltage at said load and wherein said means for executing a fuzzy inference operation uses third membership functions relating to output voltage as antecedents and rules using load membership and output voltage membership as consequents to generate said input voltage switching points.

7. A control apparatus for a UPS system of the type having

a ferroresonant transformer which has predetermined voltage regulation characteristics as a function of output load at said transformer,

a primary AC voltage source for supplying said transformer,

a secondary AC source for supplying said transformer and including an inverter circuit adapted to be energized by battery, and

transformer input switching means for selectively switching from said primary source to said secondary source and vice versa,

said control apparatus comprising:

means for sensing output current at said load and calculating output load as a percentage of full load to provide a first input signal which varies as a function of percent load,

means for sensing output voltage at said load and providing a second input signal which varies as a function of output voltage,

fuzzy inference apparatus means responsive to said first and said second input signals for dynamically generating input voltage switching points on a continuous, non-stepwise basis by executing a fuzzy inference operation using first membership functions relating to output load, second membership functions relating to output voltage, third membership functions of values relating to input voltage switching points determined by said regulation characteristics and rules using percent load membership functions selected as a function of said first input signal, output voltage membership functions selected as a function of said second input signal and values of said third membership functions as determined by said selected first and second membership functions to generate said dynamic input voltage switching points on a continuous, non-stepwise basis,

means for sensing voltage at said primary source, and

means for comparing said primary voltage to said dynamic input voltage switching points on a continuous basis to provide a control signal for said input switching means whenever said primary voltage drops below a dynamic input voltage switching point to disconnect said primary source from said regulating transformer and connect said secondary source to said regulating transformer and thereby effectively utilize said battery only when required.

8. The method of operating an uninterruptible power supply of the type having:

a ferroresonant voltage regulating transformer having predetermined regulation characteristics as a function of load,

first input means for coupling a primary AC voltage source to said transformer,

an inverter circuit adapted to be energized by a reserve DC voltage source to provide a secondary AC voltage source,

second input means for coupling said secondary AC voltage to said regulating transformer, and

output means for supplying a regulated voltage from said regulating transformer to a variable load,

said method comprising the steps of;

developing a first monitoring signal which varies with voltage at said primary source,

developing a second monitoring signal which varies with at least one electrical parameter at said load,

using said second signal to compute percent load,

performing a fuzzy inference operation to generate dynamic input voltage switching points on a continuous, non-stepwise basis by using percent load, first membership functions relating to percent load, second membership functions relating to input voltage switching points, and rules using at least load membership as antecedents and values of input voltage switching points as consequences as determined by regulation characteristics of the ferroresonant transformer to generate said dynamic input voltage switching points on a continuous, non-stepwise basis,

comparing said dynamic switching points against said first monitoring signal on a continuous basis, and

switching said transformer from primary source to said secondary source when said primary source voltage drops below said dynamic switching points so as to efficiently use said reserve source.

9. The method set forth in claim 8 further comprising the steps of:

developing a third monitoring signal which varies as a function of output voltage at said load and performing said fuzzy logic inference using said third monitoring signal, third membership functions relating to output voltage and rules using both percent load membership and output voltage membership as antecedents and values of input voltage switching points as consequents to generate said dynamic switching point.