Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Utility Patent
2000-07-17
2001-01-02
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S095000, C307S066000
Utility Patent
active
06169669
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The technical field of this invention is uninterruptable power supplies and particularly those controlled by a digital signal processor.
BACKGROUND OF THE INVENTION
Uninterruptable power supplies are used to interface critical equipment such as computers, communications systems, medical/life support systems, industrial systems and the like to an electric power utility. They are designed to provide clean, continuous electric power to the attached equipment under normal and abnormal utility power conditions. Among the types of uninterruptable power supplies those known as on-line UPS or inverter-preferred UPS are believed to offer the best line conditioning performance and the best protection to the attached equipment from utility power irregularities. These type uninterruptable power supplies provide regulated sinusoidal output voltage while maintaining sinusoidal input current at a high input power factor.
These uninterruptable power supplies offer ideal performance for many applications. Such systems provide high performance employing advanced control techniques and systems with fast response time. Analog control systems offer fast response times but have several drawbacks. Analog control systems often rely upon components susceptible to aging and variation with environmental conditions. Analog control systems often require a high component count. Analog control systems typically require circuit modifications to change controller gain or change the control algorithm. Analog control systems are often susceptible to electromagnetic interference. The typical 20 KHZ high frequency analog triangular waveform generation circuit is very sensitive to component tolerances and temperature. Change in component value caused by aging or temperature may cause such problems as DC offset in the output voltage, change in output operating frequency and change in output harmonics. Accordingly digital control of on-line uninterruptable power supplies are seen as advantageous.
SUMMARY OF THE INVENTION
This invention is uninterruptable power supply controlled by a digital signal processor. The uninterruptable power supply includes an AC to DC conversion unit, a battery, a battery charger, a battery boost circuit, a DC to AC inverter and a digital signal processor. The AC to DC conversion unit receives AC power and supplies DC on a DC bus. When AC power is received the battery charger charges the battery from the DC bus. When AC power fails, the battery boost circuit supplies DC power to the DC bus from the battery. The DC to AC inverter generates AC power for a load from the DC bus.
The digital signal processor periodically senses an input current, an input voltage, a battery current, a battery voltage, first and second DC bus voltages, an output current and an output voltage. The digital signal processor controls the AC to DC conversion unit to present a stable input power factor to the AC power input via an inner current loop dependent upon the input current and the outer voltage loop dependent upon an input voltage. The digital signal processor controls the battery charger upon receipt of AC power via an inner current loop dependent upon battery current and an outer voltage loop dependent upon the difference between battery voltage and first DC bus voltage. The digital signal processor controls the battery boost circuit upon failure of AC power via an inner current loop dependent upon battery current and an outer voltage loop dependent upon the difference between the battery voltage and the first DC bus voltage. The digital signal processor controls the DC to AC inverter to supply stable AC power via an inner current loop dependent upon output current and outer voltage loop dependent upon an output voltage.
The digital signal processor calculates the inner current loops controlling the AC to DC conversion unit, the battery charger, the battery boost circuit and the DC to AC inverter each predetermined time interval. The digital signal processor calculates the outer voltage loops in controlling the AC to DC conversion unit, the battery charger, the battery boost circuit and the DC to AC inverter every two predetermined time intervals. The digital signal processor preferably alternately senses a first group of signals consisting of the input voltage, the input current, the output voltage and the output current and a second group of signals consisting of the battery voltage, the battery current, the first DC bus voltage and a second DC bus voltage. The timing of the input signal sensing and the respective current loop and voltage loop calculations are timed by one or more repetitive interrupt timers.
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Berhane Adolf Deneke
Brady III W. James
Marshall, Jr. Robert D.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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