Abstract: A device and method for reading optical marks are disclosed. The device, an optical mark reader (OMR) has an array of photo sensors with light-emitting diodes (LEDs), which are driven by digital-to-analog converters (DACs), which are in turn controlled by a microcontroller. When calibrating the OMR, the sensors read a white card, and the microcontroller adjust the DACs so that the outputs of all sensors are at a voltage close to the saturation points of the photo-transistors in the sensors so that the maximum useable ranges of the sensors are utilized. The sensors then read one or more patterns of known grayscales and their response voltages are recorded. The microcontroller generates an array of voltage values as a function of grayscale for each sensor and store the values in a memory device. When reading an optical marks, the sensor output voltage in response to a mark is looked up in the table of voltages values stored in the memory device to determine the grayscale of the mark.

Abstract: A charging control circuit for severe battery conditions and an uninterruptible power supply (UPS) system including same are presented. The charging control circuit utilizes both hardware and microprocessor control to allow the UPS to start with depleted or no batteries installed. Initially, the hardware control loops regulate DC bus voltage generation to charge the batteries to a safe level to allow the UPS housekeeping circuitry to wake up and assume control of the UPS operation. Once the microprocessor has awoken, it assumes control of the DC bus and charging of the batteries. If no batteries are installed, the hardware control loop utilizes a fast responding voltage mode control to regulate the DC bus, while a microprocessor-based current mode control is used when batteries are installed. Hardware over voltage control and microprocessor shut off control is also provided.

Abstract: A modular uninterruptible power supply is presented having multiple power modules installed therein. Each of the individual power modules contains an internal bypass circuit sized for its particular power module. Preferably internal bypass circuitry is sized to carry two per unit load. The system and method of the invention also includes internal control circuitry for each of the modular power modules that control transitions between the inverter and bypass modes of operation. This transition control is coordinated with the other controllers for the other modular power modules installed in the uninterruptible power supply. Both the high speed communication bus and a high level interrupt line are utilized to minimize the transfer break time between different modes of operation while ensuring that the inverter is never paralleled with the utility line voltage. To further minimize this transfer time, a solid state switching circuit is utilized to provide the initialization between operational modes.

Abstract: Presented is a center switching circuit and an inverter and an uninterruptible power supply (UPS) utilizing same. The center switching circuit selectively enables and disables power flow to and from the bus capacitors of an inverter or UPS. As such, the center switching circuitry effectively removes the bus capacitors from the circuit. This allows operation of the inverter or UPS in a high efficiency mode whereby input line voltage may be passed essentially without compensation to the output when the center switching circuit is open. Modulation of the center switching circuit during this mode provides soft charging of the bus capacitors so that they are available to source current in a double-conversion or DC boost mode upon degradation or loss of the line voltage. To supply output power from the bus capacitors, the center switching circuit is closed to associate these capacitors with the neutral.

Abstract: A line-interactive single conversion uninterruptible power supply (UPS) utilizing a multiple tapped ferroresonant transformer and a square wave PWM inverter is presented. During normal utility line operation, the line voltage is not modified in any way, except for ferroresonant filtering and regulation. Tap control circuitry insures proper tap selection based on the utility input voltage. During tap transitions in utility out of specification operation, a second power source, such as an inverter, is operated to provide output power to the connected loads. The control of the inverter switching angles may be accomplished through a look-up table. This look-up table contains the converter pulse widths for monitored battery voltage. No output voltage feedback is required. Based on the inherent regulation provided by the ferroresonant transformer, the PWM control may be accomplished in course steps.

Abstract: A standby power system is provided having power conversion, output voltage control, and line-fault detection systems that make possible a significant reduction in the cost of the system. The standby power system provides backup power to a load, such as a computer system, when main AC line power fails. A system DC battery voltage is converted to an AC output voltage signal at line voltage levels by a power conversion system including a high frequency push-pull inverter, a light-weight low-cost high frequency transformer, a rectifier, and a line frequency inverter. The high frequency inverter is controlled to provide high frequency battery voltage pulse bursts separated by low frequency zero voltage dead times which are boosted by the transformer to line voltage levels and rectified by the rectifier. The line frequency inverter is controlled to provide the rectified line voltage level pulse bursts to the standby power system output in the form of a stepped square wave output signal at line frequencies.

Abstract: Instabilities in the output voltage provided from an AC power supply system such as an uninterruptible power supply connected to a power factor correcting load are suppressed by a dynamic voltage regulation stabilizer system which is connected across the output lines from the power supply system to the load. The DVR stabilizer system includes a rectifier connected to the power supply system output lines. A capacitor is connected across the output nodes of the rectifier. Switching devices form a bridge that connects the capacitor to the output lines. Selected switching devices in the bridge are turned on for a selected duration encompassing the time of the peak of each half-cycle of the AC voltage waveform provided by the power supply system. During normal operation, where the peak AC voltage from the power supply system is substantially constant, the capacitor charges up through the rectifier to a voltage level near the peak value of the AC voltage waveform.

Abstract: A back-up uninterruptible power system has a power supply path from input terminals connected to AC power system lines to normally supply power to a load. Upon the occurrence of a line fault, a static switch in the power supply path interrupts the connection between the AC power lines and the load and an inverter is turned on to provide power derived from an auxiliary battery through a transformer to the power supply path to supply AC power to the load. By using the static switch, switching from line connection to backup power can be done quickly, within a half cycle, so that substantially no interruption of the output waveform is observed. The inverter can be operated to provide a commutation pulse to the SCRs in the static switch to commutate an SCR which might otherwise continue conducting after the triggering signals to the gates are cut off and before the inverter supplies the AC power to the load.