Standby power system
First Claim
1. A standby power system including input terminals adapted to be connected to a source of AC power at line frequency and line voltage levels and output terminals adapted to be connected to a load, the load being provided with line power from the source of AC power under normal line operating conditions, a battery, and a power conversion system for providing backup AC power at the line frequency and line voltage levels to the output terminals from the battery voltage to provide backup power to the load when a failure of the source of AC power is detected, the power conversion system comprising:
- (a) a high frequency transformer having a primary winding and a secondary winding;
(b) a high frequency inverter including first and second high frequency switching devices, responsive to high frequency switching control signals to turn the high frequency switching devices on, and connected between the battery and the primary winding of the transformer such that when the first high frequency switching device is turned on the battery voltage is applied in a first polarity to the primary winding of the transformer and when the second high frequency switching device is turned on the battery voltage is applied in a second polarity to the primary winding of the transformer, the high frequency transformer and high frequency inverter thereby operating together to boost the battery voltage applied to the primary winding of the transformer to approximately the line voltage level at the secondary winding of the transformer;
(c) a rectifier connected to the secondary winding of the transformer to rectify a signal appearing on the secondary winding to provide a rectified power signal;
(d) a line frequency inverter including first and second line frequency switching devices, responsive to line frequency switching control signals to turn the line frequency switching devices on, and connected between the rectifier and the output terminals of the standby power system such that when the first line frequency switching device is turned on the rectified power signal is applied in a first polarity to the output terminals of the standby power system and when the second line frequency switching device is turned on the rectified power signal is applied in a second polarity to the output terminals;
(e) high frequency modulator means for providing high frequency switching control signals at a high frequency alternately to the first and second high frequency switching devices and for periodically interrupting the providing of the high frequency switching control signals at a rate of approximately twice the line frequency, thereby providing high frequency battery voltage pulse bursts separated by lower frequency dead times to the primary winding of the transformer causing approximately line voltage level high frequency pulse bursts separated by lower frequency dead times to appear on the secondary winding of the transformer and be rectified by the rectifier into the rectified power signal; and
(f) output voltage controller means for providing line frequency switching control signals at a low frequency to the first and second line frequency switching devices to apply the rectified power signal in alternating first and second polarities to the output terminals to provide a stepped square wave output signal at the line frequency and line voltage levels on the output terminals, wherein the stepped square wave output signal includes positive and negative voltage steps corresponding to the high frequency pulse bursts on the secondary winding of the transformer separated by zero-voltage dead times corresponding to the lower frequency dead times on the secondary winding of the transformer.
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Accused Products
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. Rms and peak output voltage control is provided by a system controller based on a single digital output voltage control signal. The system controller detects the occurrence of AC line faults using a single digital line sense signal. Since analog-to-digital conversion of the power system input and output voltage waveforms is not required for line fault detection or output voltage control, the system controller may be implemented using a low-cost microprocessor.
195 Citations
35 Claims
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1. A standby power system including input terminals adapted to be connected to a source of AC power at line frequency and line voltage levels and output terminals adapted to be connected to a load, the load being provided with line power from the source of AC power under normal line operating conditions, a battery, and a power conversion system for providing backup AC power at the line frequency and line voltage levels to the output terminals from the battery voltage to provide backup power to the load when a failure of the source of AC power is detected, the power conversion system comprising:
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(a) a high frequency transformer having a primary winding and a secondary winding; (b) a high frequency inverter including first and second high frequency switching devices, responsive to high frequency switching control signals to turn the high frequency switching devices on, and connected between the battery and the primary winding of the transformer such that when the first high frequency switching device is turned on the battery voltage is applied in a first polarity to the primary winding of the transformer and when the second high frequency switching device is turned on the battery voltage is applied in a second polarity to the primary winding of the transformer, the high frequency transformer and high frequency inverter thereby operating together to boost the battery voltage applied to the primary winding of the transformer to approximately the line voltage level at the secondary winding of the transformer; (c) a rectifier connected to the secondary winding of the transformer to rectify a signal appearing on the secondary winding to provide a rectified power signal; (d) a line frequency inverter including first and second line frequency switching devices, responsive to line frequency switching control signals to turn the line frequency switching devices on, and connected between the rectifier and the output terminals of the standby power system such that when the first line frequency switching device is turned on the rectified power signal is applied in a first polarity to the output terminals of the standby power system and when the second line frequency switching device is turned on the rectified power signal is applied in a second polarity to the output terminals; (e) high frequency modulator means for providing high frequency switching control signals at a high frequency alternately to the first and second high frequency switching devices and for periodically interrupting the providing of the high frequency switching control signals at a rate of approximately twice the line frequency, thereby providing high frequency battery voltage pulse bursts separated by lower frequency dead times to the primary winding of the transformer causing approximately line voltage level high frequency pulse bursts separated by lower frequency dead times to appear on the secondary winding of the transformer and be rectified by the rectifier into the rectified power signal; and (f) output voltage controller means for providing line frequency switching control signals at a low frequency to the first and second line frequency switching devices to apply the rectified power signal in alternating first and second polarities to the output terminals to provide a stepped square wave output signal at the line frequency and line voltage levels on the output terminals, wherein the stepped square wave output signal includes positive and negative voltage steps corresponding to the high frequency pulse bursts on the secondary winding of the transformer separated by zero-voltage dead times corresponding to the lower frequency dead times on the secondary winding of the transformer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A standby power system including input terminals adapted to be connected to a source of AC power at line frequency and line voltage levels and output terminals adapted to be connected to a load, the load being provided with line power from the source of AC power under normal line operating conditions, a battery, and a power conversion system for providing backup AC power at line frequency and line voltage levels on the output terminals from the battery voltage to provide backup power to the load when a failure of the source of AC power is detected, the power conversion system comprising:
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(a) power conversion means for providing a stepped square wave output signal at line frequency and line voltage levels to the output terminals of the standby power system from the battery voltage, the stepped square wave output signal including positive and negative voltage steps separated by zero-voltage dead times; and (b) output voltage controller means for varying the duration of the voltage steps and the zero-voltage dead times of the stepped square wave output signal to control the rms voltage level of the output signal, including means for determining the rms voltage level of the stepped square wave output signal, means for providing an output voltage control signal when the rms voltage level of the output signal exceeds an rms output voltage level threshold, and means for terminating a positive or negative voltage step in the output signal to initiate the zero-voltage dead time in response to the providing of the output voltage control signal. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28)
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29. A method for providing an AC power signal at line frequency and line voltage levels to the output terminals of a power system such as a backup power system from the voltage provided by a battery, comprising the steps of:
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(a) alternately connecting opposite polarities of the battery voltage at a high frequency to the primary winding of a high frequency transformer such that the battery voltage is boosted to approximately the line voltage level on a secondary winding of the transformer; (b) periodically interrupting the step of connecting the battery voltage to the transformer at a rate of twice the line frequency such that high frequency positive and negative battery voltage pulse bursts separated by lower frequency dead times are applied to the primary winding of the transformer causing approximately line voltage level high frequency positive and negative pulse bursts separated by lower frequency dead times to appear on the secondary winding of the transformer; (c) rectifying the high frequency pulse bursts appearing on the secondary winding of the transformer to provide a rectified power signal; and (d) applying the rectified power signal in alternating polarities to the output terminals to provide a stepped square wave output signal at line frequency and line voltage levels on the output terminals, wherein the stepped square wave output signal includes positive and negative voltage steps corresponding to the high frequency pulse bursts on the secondary winding of the transformer separated by zero-voltage dead times corresponding to the lower frequency dead times on the secondary winding of the transformer. - View Dependent Claims (30, 31, 32, 33, 34, 35)
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Specification