US 5,602,462 A · Uninterruptible power system

Abstract

An uninterruptible power system has a transformer with a primary connected to input terminals, a secondary connected to output terminals, a static switch connected between the input terminals and the primary, and an auxiliary primary connected to an inverter which is supplied by a battery to provide output voltage to the output terminals when a main AC power system connected to the input terminals has failed. The primary has multiple taps at different voltage levels and a buck-boost winding. The taps of the transformer are switched and the buck-boost winding is controlled to provide either buck, boost, or pass-by to allow control of the output voltage from the transformer to within a few percent of a desired voltage level despite large changes in the input voltage. A battery charger coupled to the auxiliary primary operates as a boost converter to provide current to charge the battery at a current level which tracks the input voltage from the AC power system, thereby providing a substantially unity power factor to the AC power system. The voltage control of the output voltage also controls the voltage at the output of the auxiliary primary to which the battery charger is connected, whereby the voltage applied to the charger is substantially regulated and the output power of the charger itself is substantially regulated. The charger can be operated in programmable modes to provide a desired charge configuration for the battery. Detection of faults in the AC power system is enhanced by accurate detection of the zero crossings of the input voltage from the AC power system, and by comparison of the AC input power waveform with an adaptive reference.

Claims51

Dependent claims

An uninterruptible power system of the type having AC input terminals which may be connected to an AC power system, AC output terminals to which a load may be connected, a transformer with a primary connected to receive AC input power provided to the AC input terminals, a secondary connected to the output terminals, and an auxiliary primary, an inverter connected to the auxiliary primary, a battery supplying DC power to the inverter, the inverter adapted to switch to provide alternating polarity of the battery voltage across the auxiliary primary to provide AC output power at the secondary and at the output terminals to supply the load when power from the AC power system is not available, the improvement comprising:

(a) a plurality of primary tap switches connected between the input terminals and the primary and placed at different effective voltage levels along the primary;
(b) tap closing means for closing a selected one of the plurality of primary tap switches in response to a primary tap control signal;
(c) a buck-boost winding on the transformer;
(d) buck-boost winding switching means connected to the primary and the buck-boost winding for selectively responding to a buck-boost control signal to connect the buck-boost winding to act as a boost to effectively increase the secondary to primary turns ratio by passing an opposing current through the buck-boost winding so as to create a flux in the transformer in opposition to a flux in the primary, to act as a buck to effectively reduce the secondary to primary turns ratio by passing an aiding current running in a direction through the buck-boost winding so as to create a flux in the transformer aiding the flux in the primary, or to be bypassed altogether such that there is no current in the buck-boost winding to provide a normal turns ratio between the secondary and primary;
and
(e) control means for providing the primary tap control signal to close a selected one of the primary tap switches and for providing the buck-boost winding control signal to connect the buck-boost winding so that the voltage level at the output terminals is maintained within a selected range of a preferred output voltage level despite changes in the voltage level at the input terminals.

3 more elements

A method for regulating AC output power in an uninterruptible power system of the type having AC input terminals which may be connected to an AC power system receive power therefrom, output terminals to which a load may be connected, a transformer with a primary connected to receive AC input power provided to the input terminals, a secondary connected to the output terminals, and an auxiliary primary, an inverter connected to the auxiliary primary, a battery supplying DC power to the inverter, the inverter adapted to switch to provide alternating polarity of the battery voltage across the auxiliary primary to provide AC output power at the secondary and the output terminals to supply the load when power from the AC power system is not available, comprising the steps of:

closing one of a plurality of primary tap switches connected between the input terminals and the primary and placed at different effective voltage levels along the primary, and providing one of an additional flux in the transformer in opposition to a flux in the primary, an additional flux in the transformer aiding the flux in the primary, or no additional flux so that the voltage level at the output terminals is maintained near a preferred output voltage level as the voltage level at the input terminals changes.

An uninterruptible power system comprising:

(a) an inverter, AC input terminals which may be connected to an AC power system, a battery supplying DC power to the inverter, output terminals, and switching means for providing AC power to the output terminals from the input terminals when the AC power system power is available and switching to provide power from the inverter to the output terminals when the AC power system fails;
(b) means for monitoring an AC power system input voltage waveform provided at the input terminals, and providing a measured value thereof;
(c) means for adding a tolerance voltage level to the measured input voltage waveform to form an adjusted input voltage waveform;
(d) means for adding the tolerance voltage level to a reference voltage waveform to form an adjusted reference voltage waveform;
(e) means for comparing the adjusted reference voltage waveform with the measured input voltage waveform;
(f) means for comparing the adjusted input voltage waveform with the reference voltage waveform;
(g) means for indicating a power system failure if either the adjusted reference voltage waveform is less than the measured input voltage waveform or the adjusted input voltage waveform is less than the reference voltage waveform;
(h) means for increasing the tolerance voltage levels when the number of power system failure indications over a selected duration exceeds a selected number;
and
(i) means for reducing the tolerance voltage level when there are no power system failure indications over a second selected duration.

7 more elements

A method for charging a battery in an uninterruptible power system of the type having AC input terminals which may be connected to an AC power system, a transformer with a primary connected to receive AC input power provided at the input terminals, a secondary connected to output terminals connectable to a load, and an auxiliary primary, an inverter connected to the auxiliary primary, a battery supplying DC power to the inverter, the inverter adapted to switch to provide alternating polarity of the battery voltage across the auxiliary primary to provide AC output power at the secondary to supply the load when power from the AC power system is not available, and a battery charger connected to the auxiliary primary which acts as a secondary when power from the AC power system is available, comprising the steps of:

(a) monitoring the voltage of the battery and providing a battery monitoring signal indicating the voltage level on the battery;
(b) entering a constant power mode when input power from the AC power system becomes available after the inverter has been providing AC output power, and wherein the battery is charged by the charger at a normal charge voltage level until the battery monitoring signal indicates that the battery has been charged to the normal charge voltage level;
(c) entering a maintenance mode when the battery has been charged to the normal charge voltage level by the constant power mode in less than or equal time to a selected charging time duration, and wherein the battery is then charged by the charger at a maintenance voltage level which is less than the normal charge voltage level;
(d) entering a constant voltage mode when the battery has been charged to the normal charge voltage in the constant power mode in more time than a selected charging time duration, and wherein the battery is then charged by the charger at a normal charge voltage level for a selected constant voltage duration, and thereafter entering the maintenance mode when the constant voltage duration has expired;
(e) entering a periodic mode at a periodic interval wherein the battery is charged by the charger at a normal charge voltage level for a periodic charge duration, and entering the maintenance mode when the periodic charge duration has expired;
and
(f) controlling the battery charger to implement the charger mode selection.

4 more elements

An uninterruptible power system of the type having AC input terminals which may be connected to an AC power system, a transformer with a primary connected to receive AC input power provided at the input terminals, a secondary connected to output terminals connectable to a load, and an auxiliary primary, an inverter connected to the auxiliary primary, a battery supplying DC power to the inverter, the inverter adapted to switch to provide alternating polarity of the battery voltage across the auxiliary primary to provide AC output power at the secondary to supply the load when power from the AC power system is not available, and a battery charger connected to the auxiliary primary which acts as a secondary when power from the AC power system is available, the improvement comprising:

(a) means for monitoring the voltage of the battery and providing a battery monitoring signal indicating the voltage level on the battery;
(b) means for controlling the battery charger to enter a constant power mode when input power from the AC power system becomes available after the inverter has been providing AC output power, and wherein the battery is charged by the charger at a normal charge voltage level until the battery monitoring signal indicates that the battery has been charged to the normal charge voltage level;
(c) means for controlling the battery charger to enter a maintenance mode when the battery has been charged to the normal charge voltage level in the constant power mode in less than or equal time to a selected charging time duration, and wherein the battery is then charged by the charger at a maintenance voltage level which is less than the normal charge voltage level;
(d) means for controlling the battery charger to enter a constant voltage mode when the battery has been charged to the normal charge voltage in the constant power mode in more time than the selected charging time duration, and wherein the battery is then charged by the charger at a normal charge voltage level for a selected constant voltage duration, and thereafter for controlling the charger to enter the maintenance mode when the constant voltage duration has expired;
and
(e) means for controlling the battery charger to enter a periodic mode at a periodic interval, and wherein the battery is charged at a normal charge voltage level by the charger for a selected periodic charge duration, and to enter the maintenance mode when the periodic charge duration has expired.

3 more elements

A battery charger for an uninterruptible power system of the type having AC input terminals which may be connected to an AC power system and AC output terminals to which a load may be connected, with a power path between the AC input and output terminals, and a battery connected to an inverter to supply AC output power to the output terminals when the AC power system connected to the input terminals has failed, comprising:

(a) a boost converter connected to receive power from the AC power system connected to the input terminals and to provide DC power to the battery to charge the battery, the boost converter having a rectifier connected to the power path to receive AC input power and providing a rectified DC output voltage and an inductor and a controllable switch connected in series to provide a current path from the DC output of the rectifier through the inductor and the controllable switch back to the rectifier when the switch is closed, a node connecting the controllable switch and the inductor connected through a diode to the battery so that current from the inductor flows to the battery when the controllable switch is opened;
(b) a timer having an output connected to the controllable switch to provide an on and off signal to open and close the controllable switch at a high frequency, the times responsive to control signals to control at least the on-time of the timer output control signal during which the controllable switch is closed;
and
(c) current control means for monitoring the current flowing through the controllable switch when it is closed and for comparing the value of the current to the output voltage of the rectifier and connected to control the timer to turn off the output signal of the timer to the controllable switch to open the controllable switch when the current through the controllable switch reaches a level proportional to the DC output voltage of the rectifier, whereby the maximum input current to the charger tracks the AC input voltage so as to present a substantially unity power factor to the AC power system which is providing power to the charger.

1 more element

Dependencies are inferred from the claim text.

Uninterruptible power system

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Uninterruptible power system

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Abstract

Claims51