An uninterrupted power supply device is disclosed having an at least 3-phase AC power supply input for connection of an AC power supply, a DC power supply input for connection of a DC power supply, a power output for connection of a load, a power conversion unit, which interconnects the AC power supply input, the DC power supply input and the power output, whereby the uninterrupted power supply device comprises a secondary control reference, a measurement unit for measuring a voltage difference between the internal control reference and the secondary control reference, and a switching unit for connecting the internal control reference to the secondary control reference when the measured voltage difference is bigger than a threshold voltage and the AC power supply is disconnected from the uninterrupted power supply device.

Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for non-isolated power conversion. In one aspect, a method includes generating first and second rectified outputs using a rectifier with a first input and a second input connected respectively to a first and second output of a power source, capacitively coupling the first and second rectified outputs to a neutral, generating first and second AC outputs from the first and second rectified outputs, and capacitively coupling the first and second AC outputs to the neutral. Other embodiments of this aspect include corresponding systems, apparatus, and computer programs, configured to perform the actions of the methods, encoded on computer storage devices.

According to one aspect, embodiments of the invention provide a power supply system comprising an input configured to receive input AC power from an input power source, an output configured to provide output AC power to a load, a converter coupled to the input and configured to convert the input AC power into converted DC power, a first DC bus coupled to the converter and configured to receive the converted DC power, an inverter coupled to the first DC bus and the output and configured to convert DC power from the first DC bus into the output AC power, a first DC switch circuit coupled between the first DC bus and neutral and a controller coupled to the first DC switch circuit and configured to operate the first DC switch circuit such that voltage on the first DC bus is zero during switching operation of the converter and the inverter.

According to one aspect, embodiments of the invention provide a UPS comprising a plurality of DC busses configured to receive DC power from a converter, the plurality of DC busses including a positive DC bus configured to maintain a positive DC voltage level, a mid-point DC bus, and a negative DC bus configured to maintain a negative DC voltage level, a 3-level inverter coupled to the plurality of DC busses and configured to convert the DC power from the plurality of DC buses into output AC power, and a controller configured to monitor the positive and negative DC voltage levels, identify an imbalance between the positive and negative DC voltage levels, and selectively control, based on the imbalance, the 3-level inverter to operate in a 2-level mode of operation and a 3-level mode of operation to transfer energy between the positive and negative DC busses.

The present application discloses a direct current (DC) converter including a voltage divider for dividing a voltage provided by a DC voltage source, having a positive DC voltage input terminal, a negative DC voltage input terminal, and a divided voltage output terminal; a conversion circuit having a first switch, a second switch, an inductor unit, a first unidirectional conductor, and a second unidirectional conductor; a positive converted voltage output terminal; and a negative converted voltage output terminal.

An uninterruptible power supply adapted to be connected between an AC line and a load a battery system for storing battery power, an inverter, a transformer, and a controller. The inverter is operatively connected to the battery system. The transformer comprises a primary winding adapted to be operatively connected to the AC line, a load winding adapted to be operatively connected to the load, and an inverter winding operatively connected to the inverter. The controller controls the inverter to operate in a first mode in which the inverter supplies power to the battery system, a second mode in which the inverter supplies power to the load winding using battery power stored in the battery system, and, based on a cost value indicative of reduction of life of the battery system, a third mode in which the inverter supplies power to the primary winding using battery power stored in the battery system.

A power converter can include an inverter including, connected in series, switching elements, the inverter circuit being connected to both ends of a DC power source series circuit resulting from connecting in series a DC power source and a DC power source. Also included can be an AC output terminal that is connected to a connection point of the switching element and the switching element, an AC output terminal that is connected to a connection point of the DC power source and the DC power source, a bidirectional switch element one end of which is connected to the AC output terminal and the other end of which is connected to a terminal of an AC power source and a bidirectional switch element one end of which is connected to the AC output terminal and the other end of which is connected to the AC power source.

A device includes at least one isolating transformer. An input is coupled to the at least one isolating transformer and configured to receive input from an energy source. At least one power switch is coupled to the isolating transformer. A diode is coupled to the at least one isolating transformer. An energy storage medium is coupled to the diode. An inverter includes one or more inverter switches, an inverter input, and an inverter output. The inverter input is coupled to the diode and the energy storage medium. The inverter output is configured to be coupled to the power network, and the inverter is configured to create AC power for distribution to the power network. A controller is configured to modulate the at least one power switch to control power flow from the input and to modulate the state of the inverter switches to control power flow to the power network.

A power converter that can supply constant voltage to a load even upon fluctuation of voltage of an AC power source includes an inverter circuit resulting from connecting switching elements in series, the inverter circuit being connected to both ends of a DC power source series circuit resulting from connecting in series two DC power sources; an AC output terminal that is connected to a connection point of the switching elements; another AC output terminal that is connected to a connection point of the DC power sources; and a bidirectional switch element including one end connected to the AC output terminal U and another end connected to a terminal of an AC power source.

According to one aspect, embodiments of the invention provide a method of operating a UPS system, the method comprising receiving, at an input of a first UPS, input power from a power source, generating, with a first analysis circuit, a first signal indicative of a characteristic of the input power, receiving, at the analysis circuit, a second signal from a second analysis circuit of a device coupled to the power source, the second signal indicative of a characteristic of input power received at the second analysis circuit, analyzing with the analysis circuitry, the first signal and the second signal, determining, whether an improper wiring condition exists at the input, in response to a determination that an improper wiring condition does not exist, providing output power to an output of the first UPS, and in response to a determination that an improper wiring condition does exist, de-energizing the first UPS.