US 5,182,518 A · Inverter and battery testing for uninterruptible power systems

Abstract

The inverter of an uninterruptible power system is tested by turning on switches in the inverter at a selected test phase in each half-cycle of the AC input waveform so that the inverter provides a voltage which opposes the AC input voltage waveform during part of each half-cycle of the waveform. The resulting current drawn from the inverter battery, if any, is measured and its peak may be found. The peak battery current during each half-cycle is compared to maximum allowable peak currents to determine if an inverter failure has occurred. If the peak currents are lower than a maximum acceptable value, the test is repeated on a subsequent AC input waveform at a decreased test phase (a shorter time delay from the zero crossing of each half-cycle of the waveform) until the peak current in the first half-cycle is at a selected value, at which time the peak in the second half-cycle is checked to determine if it is within an acceptable range. If not, an inverter test failure is indicated. Inverter test failure is also indicated if repeated cycles during which the test phase is reduced fail to cause the first peak to reach the proper value and the test phase is finally reduced to a minimum allowable test phase. If the inverter has been tested and is found to be operating properly, a battery test can be conducted by selectively disconnecting the AC power system from the load, turning on the inverter for a selected period of time, and detrmining remaining available run time based on the battery voltage while the inverter was running.

Claims43

Dependent claims

A method for testing an inverter which receives power from a DC source such as a battery and which is adapted to provide an AC output voltage from the inverter by switching the polarity of the voltage from the DC source, comprising the steps of:

(a) coupling the output of the inverter to a power system which provides an AC voltage to a load so that the voltage provided from the inverter can be applied against the AC voltage waveform from the power system;
(b) turning on the inverter at a test phase corresponding to a chosen point in time after the start of a half-cycle of the AC power system voltage to apply a voltage coupled to the power system which is of the same polarity as the AC voltage waveform at that time and turning off the inverter at a selected point thereafter in the half-cycle of the waveform;
and
(c) measuring the current flowing from the inverter during the time it is on such that the measured current can be compared with acceptable values of current to determine whether the inverter is properly functioning.

1 more element

(a) coupling the output of the inverter to a power system which provides an AC voltage to a load so that the voltage provided from the inverter can be applied against the AC voltage waveform from the power system;
(b) turning on the inverter at a test phase corresponding to a chosen point in time after the start of a half-cycle of the AC power system voltage to apply a voltage coupled to the power system which is of the same polarity as the AC voltage waveform at that time and turning it off at a selected point thereafter in the half-cycle of the waveform, and turning on the inverter during the second half-cycle of the waveform at the same test phase after the start of the second half-cycle of the AC power system waverform to apply a voltage coupled to the power system which is of the same polarity as the AC voltage waveform at that time and turning it off at a selected point thereafter in the second half-cycle of the waveform;
(c) measuring the peak current flowing from the inverter during the time that it is on in each half-cycle to determine a first peak current and a second peak current;
(d) then, determining whether a limit condition has occurred, the limit condition selected from the group consisting of (i) the first peak exceeding a selected maximum allowable peak value, (ii) the second peak exceeding a maximum allowable peak value, (iii) the first and second peaks deviating in value from each other by greater than a selected maximum deviation, (iv) the test phase being smaller than a selected minimum test phase, (v) combinations of limit conditions (i) through (iv), and (vi) the first peak being substantially at a selected value and the second peak being within a selected range about that value of the first peak, and if any of the limit conditions (i) through (v) are found, providing an indication of inverter test failure;
(e) if any limit condition is found, then terminating the inverter test;
(f) if a limit condition is not found, delaying for a selected period of time which spans several cycles of the AC voltage input waveform, then reducing the value of the test phase by a selected amount;
and
(g) then, repeating steps (b) through (f) until a limit condition is reached.

5 more elements

A method of testing a battery supplying power to an inverter for an uninterruptible power system which can be selectively coupled to a load, the load also receiving power coupled thereto from an AC power system, comprising the steps of:

(a) disconnecting power from the power system to the load and turning on the inverter to provide power from the battery through the inverter to the load;
(b) while the inverter is running, measuring the battery voltage;
(c) then, turning off the inverter and reconnecting power from the power system to the load;
(d) calculating the remaining run time of the battery based on the measured battery voltage, the rated ampere hour capacity of the battery, the full charge voltage of the battery, and the minimum allowable battery voltage at which power can be provided from the battery to the load;
and
(e) providing a low battery indication if the calculated remaining run time is less than a selected value.

3 more elements

An improved uninterruptible power system of the type having a transformer with a primary connectable to an AC power system, a secondary connectable to a load, and an auxiliary primary, an inverter connected to the auxiliary primary and 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, the improvement comprising:

(a) control means for turning on the inverter to test the inverter while AC power is available from the AC power source at a test phase corresponding to a chosen point in time after the start of a half-cycle of the AC power system voltage to apply a voltage across the transformer which is of the same polarity as the AC voltage waveform at that time and turning off the inverter at a selected point thereafter in the half-cycle of the waveform;
and
(b) means for measuring the current flowing from the inverter during the time that it is on, the control means comparing the measured current with acceptable values of current to determine whether the inverter is properly functioning.

Dependencies are inferred from the claim text.

Inverter and battery testing for uninterruptible power systems

Life of this patent

Inverter and battery testing for uninterruptible power systems

Life of this patent

Abstract

Claims43