Uninterruptible power system

• US 20020039302A1
• Filed: 10/01/2001
• Published: 04/04/2002
• Est. Priority Date: 09/29/2000
• Status: Active Grant

• Current Assignee: Sanyo Denki Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Denki Company Limited (Panasonic Holdings Corporation)
• Inventors: Nagai, Masahiko, Yanagisawa, Minoru, Hanaoka, Hiroyuki
• Granted Patent: US 6,496,394 B2
• Time in Patent Office: Days
• US Class Current: 363/71
• CPC Class Codes: H02J 9/062 for AC powered loads
• CPC Class Codes: H02M 3/1584 with a plurality of power processing stages connected in parallel
• CPC Class Codes: H02M 7/493 the static converters being arranged for operation in parallel

Abstract

A parallel operation-type uninterruptible power system capable of preventing one of uninterruptible power systems from being extremely increased in load sharing ratio without having to operate each uninterruptible power system while watching operation of the remaining uninterruptible power systems. The uninterruptible power systems each are constituted by an inverter circuit and an inverter circuit control device. The inverter circuit control device includes a PWM control signal generating means. The PWM control signal generating means generates a PWM control signal so as to gradually reduce an output voltage of the inverter circuit as supply active power increases and until a judging means judges that the supply active power has reached a predetermined level and so as to reduce the output voltage at a reduction ratio increased as compared with before to keep it from falling into an overload condition when the judging means judges that the supply active power has reached the predetermined level.

Claims

1. An uninterruptible power system comprising:

an inverter circuit for converting DC power converted from AC power of a commercial power supply into AC power to output it to a load when said commercial power supply is in a normal condition and converting DC power of a storage battery into AC power to output it to the load when said commercial power supply falls into a power failure condition;

said inverter circuit being constituted by semiconductor switching elements;

an inverter circuit control device including a voltage detecting means for detecting an output voltage of said inverter circuit, a current detecting means for detecting an output current of said inverter circuit, and a PWM control signal generating means for generating a PWM control signal for subjecting said semiconductor switching elements constituting said inverter circuit to PWM control to permit said inverter circuit to output said AC power synchronized with commercial power while adjusting an output voltage thereof;

said PWM control signal generating means including a differential amplifying circuit for amplifying a difference between said output voltage and a sinusoidal reference signal and being constructed so as to generate said PWM control signal depending on a signal obtained by adding or subtracting said output current to or from an input or output of said differential amplifying circuit in such a manner that said output current is subtracted from the sinusoidal reference signal;

said inverter circuit control device further including an operation means for operating a supply active power being fed to said load by the inverter circuit depending on said output voltage and output current and a judging means for judging whether said supply active power operated by said operation means has reached a predetermined level before it falls into an overload condition;

said PWM control signal generating means generating said PWM control signal so as to gradually reduce said supply active power or gradually reduce said output voltage of said inverter circuit as said supply active power increases and until said judging means judges that said supply active power has reached said predetermined level and so as to reduce said output voltage at a reduction ratio increased as compared with before to keep it from falling into said overload condition when said judging means judges that said supply active power has reached said predetermined level.

2. An uninterruptible power system as defined in claim 1, wherein said PWM control signal generating means is constructed so as to subtract a value obtained by multiplying said supply active power by a first gain constant from an effective value command value for an output voltage to be obtained before said judging means judges that said supply active power has reached said predetermined level and to subtract a value obtained by multiplying said supply active power by a second gain constant larger than said first gain constant from the effective value command value for the output voltage to be obtained when said judging means judges that said supply active power has reached said predetermined level.

3. A parallel operation-type uninterruptible power system comprising:

a plurality of uninterruptible power systems connected in parallel to a load;

said uninterruptible power systems each including;

an inverter circuit for converting DC power converted from AC power of a commercial power supply into AC power to output it to the load when said commercial power supply is in a normal condition and converting DC power of a storage battery into AC power to output it to the load when said commercial power supply falls into a power failure condition;

said inverter circuit being constituted by semiconductor switching elements; and

an inverter circuit control device including a voltage detecting means for detecting an output voltage of said inverter circuit, a current detecting means for detecting an output current of said inverter circuit, and a PWM control signal generating means for generating a PWM control signal for subjecting said semiconductor switching elements constituting said inverter circuit to PWM control to permit said inverter circuit to output said AC power synchronized with commercial power supply while adjusting an output voltage thereof;

said PWM control signal generating means including a differential amplifying circuit for amplifying a difference between said output voltage and a sinusoidal reference signal and being constructed so as to generate said PWM control signal depending on a signal obtained by adding or subtracting said output current to or from an input or output of said differential amplifying circuit in such a manner that said output current is subtracted from the sinusoidal reference signal;

said inverter circuit control device further including an operation means for operating a supply active power being fed to said load by the inverter circuit depending on said output voltage and output current and a judging means for judging whether said active power operated by said operation means has reached a predetermined level before it falls into an overload condition;

said PWM control signal generating means generating said PWM control signal so as to gradually reduce said supply active power or gradually reduce said output voltage of said inverter circuit as said supply active power increases and until said judging means judges that said supply active power has reached said predetermined level and so as to reduce said output voltage at a reduction ratio increased as compared with before to keep it from falling into said overload condition when said judging means judges that said supply active power has reached said predetermined level.

4. An inverter circuit comprising:

an inverter circuit for converting AC power of a commercial power supply into DC power to output it to a load;

said inverter circuit being constituted by semiconductor switching elements; and

an inverter circuit control device including a voltage detecting means for detecting an output voltage of said inverter circuit, a current detecting means for detecting an output current of said inverter circuit, and a PWM control signal generating means for generating a PWM control signal for subjecting said semiconductor switching elements constituting said inverter circuit to PWM control to permit said inverter circuit to output said AC power synchronized with commercial power supply while adjusting an output voltage thereof;

said PWM control signal generating means including a differential amplifying circuit for amplifying a difference between said output voltage and a sinusoidal reference signal and being constructed so as to generate said PWM control signal depending on a signal obtained by adding or subtracting said output current to or from an input or output of said differential amplifying circuit in such a manner that said output current is subtracted from the sinusoidal reference signal;

said inverter circuit control device further including an operation means for operating a supply active power being fed to said load by the inverter circuit depending on said output voltage and output current and a judging means for judging whether said active power operated by said operation means reaches a predetermined level before it falls into an overload condition;

said PWM control signal generating means generating said PWM control signal so as to gradually reduce said supply active power or gradually reduce said output voltage of said inverter circuit as said supply active power increases and until said judging means judges that said supply active power has reached said predetermined level and so as to reduce said output voltage at a reduction ratio increased as compared with before to keep it from falling into said overload condition when said judging means judges that said supply active power has reached said predetermined level.

5. A parallel operation-type inverter unit comprising:

a plurality of inverter units connected in parallel to a load;

said inverter units each including;

an inverter circuit for converting DC power converted from AC power into AC power to output it to a load;

said inverter circuit being constituted by semiconductor switching elements; and

an inverter circuit control device including a voltage detecting means for detecting an output voltage of said inverter circuit, a current detecting means for detecting an output current of said inverter circuit, and a PWM control signal generating means for generating a PWM control signal for subjecting said semiconductor switching elements constituting said inverter circuit to PWM control to permit said inverter circuit to output said AC power synchronized with commercial power supply while adjusting an output voltage thereof;

said PWM control signal generating means including a differential amplifying circuit for amplifying a difference between said output voltage and a sinusoidal reference signal and being constructed so as to generate said PWM control signal depending on a signal obtained by adding or subtracting said output current to or from an input or output of said differential amplifying circuit in such a manner that said output current is subtracted from the sinusoidal reference signal;

said inverter circuit control device further including an operation means for operating a supply active power being fed to said load by the inverter circuit depending on said output voltage and output current and a judging means for judging whether said active power operated by said operation means has reached a predetermined level before it falls into an overload condition;

said PWM control signal generating means generating said PWM control signal so as to gradually reduce said output voltage of said inverter circuit as said supply active power increases and until said judging means judges that said supply active power has reached said predetermined level and so as to reduce said output voltage at a reduction ratio increased as compared with before to keep it from falling into said overload condition when said judging means judges that said supply active power has reached said predetermined level.