High efficiency, no dropout uninterruptable power supply

An Uninterruptible Power Supply (UPS) structure, comprising:

• a first DC-DC converter, having a rectified utility power AC input signal, which produces an output signal;
• a second DC-DC converter, having a power input signal, which produces an output signal, wherein the rectified utility power AC input signal and the power input signal are applied simultaneously to the first DC-DC converter and the second DC-DC converter, respectively, and wherein the output signal of the first DC-DC converter is coupled to the output signal of the second DC-DC converter by a diode OR'ed connection;
• a regulated DC voltage generated by the first DC-DC converter when the rectified utility power AC input signal is above a predetermined voltage level and generated by the second DC-DC converter when the rectified utility power AC input signal is below the predetermined voltage level, such that a constant value of the regulated DC voltage is maintained;
• a battery source, which provides the power input signal to the second DC-DC converter;
• a comparator, having the regulated DC voltage as a first input signal and a transition voltage reference as a second input signal, which produces a compare output signal;
• a wave generator having the compare output signal of the comparator as an input signal and producing a waveform output signal;
• a pulse generator which produces a pulse signal;
• a latch having the compare output signal of the comparator as a first input signal, the pulse signal of the pulse generator as a second input signal, and an output signal;
• a ramp generator having the output signal of the latch as an input signal and generating an output signal;
• a reference voltage modulator, having the output signal of the ramp generator as a first input signal and a voltage reference as a second input signal, which produces an output signal;
• a first amplifier, having the regulated DC voltage as a first input signal and the output signal of the reference voltage modulator as a second input signal, which compares the first input signal and the second input signal to produce an output signal;
• a second amplifier which is driven by the output signal of the first amplifier and which produces an output signal;
• a third amplifier, having the output signal of the first amplifier as a first input signal and an offset signal as a second input signal, which produces an output signal, wherein the offset signal causes the third amplifier to operate at a lower input voltage than the second amplifier, and wherein if the rectified utility power AC input signal is below the predetermined voltage level the first amplifier increases its output signal sufficiently to overcome the offset signal;
• a first pulse-width modulator having the output signal of the second amplifier as an input signal and producing a first control signal which controls the first DC-DC converter;
• a second pulse-width modulator having the output signal of the third amplifier as an input signal and producing a second control signal which controls the second DC-DC converter;
• and
• a DC-AC converter, having the regulated DC voltage as a first input signal and the waveform output signal of the wave generator as a second input signal, which converts the regulated DC voltage to generate an AC output signal of the UPS,
• wherein during a half-cycle of the pulse signal, the pulse generator sets the latch and the regulated DC voltage proportionally tracks the voltage reference towards a minimum voltage level determined by the transition voltage reference, and when the regulated DC voltage is approximately equal to the minimum voltage level, the compare output signal of the comparator resets the latch and toggles the wave generator to reverse a first polarity of the DC-AC converter to a second polarity so that the AC output signal is a positive value as the regulated DC voltage rises to a desired voltage level.

A method for generating a quasi-square wave output of an Uninterruptible Power Supply (UPS), comprising the steps of:

• generating a direct-current (DC) regulated voltage at a high frequency, wherein generating the DC regulated voltage is performed by a first DC-DC converter of the UPS when a utility power input signal of the UPS is greater than a predetermined voltage level and wherein generating the DC regulated voltage is performed by a second DC-DC converter of the UPS when the utility power input signal is less than the predetermined voltage level;
• cyclically adjusting a reference voltage which sets the DC regulated voltage in order to ramp down the DC regulated voltage to a minimum voltage level and then ramp the DC regulated voltage back up to a desired voltage level;
• and
• applying a DC voltage to a polarity reversal switch of the UPS to change a polarity of an output signal of the polarity reversal switch periodically, thereby producing a quasi-square alternating current (AC) output waveform of the UPS.