Abstract: A device for electrically connecting a direct current (DC) microgrid to a DC bus of an electrical power network, which is operating at a higher voltage than the microgrid, comprises a pair of electrical port each configured for connection with either the DC bus or the microgrid; a DC-DC power converter operatively interconnecting the electrical ports for power transmission therebetween from a first voltage at the port connected to the DC bus to a lower second voltage at the port connected to the DC microgrid; a DC circuit breaker connected between the DC-DC power converter and one of the electrical ports for selectively conducting current therebetween; and a controller which is configured to communicate with constituent devices in the DC microgrid as well as a control center representative of the electrical power network in order to exchange information about electrical energy consumption in the DC microgrid and the larger network.

Abstract: A direct current circuit breaker comprises a mechanical relay in a first supply line configured to conduct electrical current during steady-state operation and an auxiliary relay assembly in parallel with the mechanical relay to define an auxiliary breaker path for conducting electrical current during transient operation of the circuit breaker. The auxiliary relay assembly comprises a power-semiconductor circuit configured for selective current conduction and for bidirectional current blocking when in a non-conductive state.

Abstract: A full-bridge inverter based on a unipolar switching scheme includes a first branch and a second branch in parallel between a first DC node and a second node, the first branch including a first higher switch and a first lower switch in series, and the second branch including a second higher switch and a second lower switch in series. A filter circuit includes a first inductor and a second inductor. One pin of the first inductor is coupled with a first branch conductor, and the first branch conductor is coupled between the first higher switch and the first lower switch, and an opposite pin of the first inductor is electrically coupled with a first output node. One pin of the second inductor is coupled with a second branch conductor, the second branch conductor is coupled between the second higher switch and the second lower switch, and an opposite pin of the second inductor is coupled with a second output node of the full-bridge inverter.

Abstract: A full-bridge inverter based on a unipolar switching scheme includes a first branch and a second branch in parallel between a first DC node and a second node, the first branch including a first higher switch and a first lower switch in series, and the second branch including a second higher switch and a second lower switch in series. A filter circuit includes a first inductor and a second inductor. One pin of the first inductor is coupled with a first branch conductor, and the first branch conductor is coupled between the first higher switch and the first lower switch, and an opposite pin of the first inductor is electrically coupled with a first output node. One pin of the second inductor is coupled with a second branch conductor, the second branch conductor is coupled between the second higher switch and the second lower switch, and an opposite pin of the second inductor is coupled with a second output node of the full-bridge inverter.

Abstract: Low cost and low power LED lamps exhibit current harmonic contents due to their nonlinear characteristics. A large scale lighting network requires tens to hundreds LED lamp installations, the resultant harmonic currents pollute the grid seriously. Furthermore, light intensity fluctuations are becoming a concern nowadays to many users, as a safety and a health problems. This phenomenon is mainly caused by heavy loads as they lead to voltage fluctuations and deteriorating in PQ and hence visual flickering in LED lamps. A single phase transformer-less unified power quality conditioner (UPQC) topology is provided with its controls to mitigate all PQ problems in a network.

Abstract: A bidirectional bridgeless buck-boost power converter circuit is provided that can function as both a voltage source inverter (VSI) circuit to transform direct current (DC) voltage to alternating current (AC) voltage and as a power factor corrector (PFC) circuit to transform AC voltage to DC voltage. The disclosed converter fully utilizes inductors to form a CL filter and buck-boost converter energy storage element. Thus, low inductance chokes are used in the converter, which leads to a higher power density and is more cost-effective. Further, the bridgeless configuration minimizes conduction losses of semiconductors, and coupled with the use of low inductance chokes this improves system efficiency.

Abstract: An uninterruptable power supply system is disclosed with a precharge converter for connecting to a DC link of the uninterruptable power supply system to a DC power supply, whereby the DC link comprises a first and a second DC bus line, which are both coupled to a common reference point, whereby the common reference point can be an AC power supply neutral of the uninterruptable power supply system, comprising power connectors for connecting to the DC power supply, a first and second output connector for connecting to the first and the second DC bus line, respectively, a converter circuit for receiving DC power from the power connectors and providing DC power to the first and second output connector, and a control unit for controlling operation of the converter circuit.

Abstract: A bidirectional bridgeless buck-boost power converter circuit is provided that can function as both a voltage source inverter (VSI) circuit to transform direct current (DC) voltage to alternating current (AC) voltage and as a power factor corrector (PFC) circuit to transform AC voltage to DC voltage. The disclosed converter fully utilizes inductors to form a CL filter and buck-boost converter energy storage element. Thus, low inductance chokes are used in the converter, which leads to a higher power density and is more cost-effective. Further, the bridgeless configuration minimizes conduction losses of semiconductors, and coupled with the use of low inductance chokes this improves system efficiency.

Abstract: An uninterruptable power supply system is disclosed with a precharge converter for connecting to a DC link of the uninterruptable power supply system to a DC power supply, whereby the DC link comprises a first and a second DC bus line, which are both coupled to a common reference point, whereby the common reference point can be an AC power supply neutral of the uninterruptable power supply system, comprising power connectors for connecting to the DC power supply, a first and second output connector for connecting to the first and the second DC bus line, respectively, a converter circuit for receiving DC power from the power connectors and providing DC power to the first and second output connector, and a control unit for controlling operation of the converter circuit.

Abstract: Exemplary embodiments are directed to methods and systems for producing a three-phase current to a three-phase output. Switching converters are used to generate a positive current, a negative current, and an intermediate current. The system is configured such that the produced positive current follows a path of a highest phase of a sinusoidal three-phase signal at a given time, the produced negative current follows a path of a lowest phase of the three-phase signal at the given time, and the produced intermediate current follows a path of a phase of the three-phase signal between the highest and the lowest phase at the given time. The produced currents are switched to each phase conductor of the three-phase output in sequence so that phase currents of the three-phase current are formed in the output conductors.

Abstract: Exemplary embodiments are directed to an snubber circuit and a power converter having an active circuit. The snubber circuit includes a series connection of a first diode and a first inductor connected between a first interfacing point and a first connection point, a second diode connected between a second connection point and a second interfacing point, a series connection of a third diode and a second inductor between a third interfacing point and the second connection point, a switching device connected between the first connection point and the third interfacing point, and a first capacitor connected between the first connection point and the second connection point. The first, the second, and the third diode are forward-biased along a path between the first interfacing point and the second interfacing point and through the third interfacing point.

Abstract: An exemplary method and apparatus for detecting islanding conditions of a distributed grid are disclosed, wherein transfer of power through a power electrical unit is controlled on the basis of a control reference. The apparatus includes a first stage and a second stage performing a respective portion of the method. The first stage injects a reactive component to the control reference, and, for at least one electrical quantity of the grid, determines a change in the quantity induced by the injected component, and determines, on the basis of the change in the electrical quantity, whether to move to the second stage of the method.

Abstract: A bridgeless power factor correction circuit as disclosed can include first and second input inductors, a series connection of a first diode and a first controllable semiconductor switch, and a series connection of a second diode and a second controllable semiconductor switch, the series connections being connected in parallel between positive and negative output terminals of the power factor correction circuit. The power factor correction circuit can include a switching circuit adapted to connect a capacitor between the input terminal and the output terminal such that the capacitor is connected between the first input terminal and a potential of the output terminal when input voltage connectable to the input terminals is positive and the capacitor is connected between the second input terminal and a potential of the output terminal when the input voltage connectable to the input terminals is negative.

Abstract: A bridgeless power factor correction circuit as disclosed can include first and second input inductors, a series connection of a first diode and a first controllable semiconductor switch, and a series connection of a second diode and a second controllable semiconductor switch, the series connections being connected in parallel between positive and negative output terminals of the power factor correction circuit. The power factor correction circuit can include a switching circuit adapted to connect a capacitor between the input terminal and the output terminal such that the capacitor is connected between the first input terminal and a potential of the output terminal when input voltage connectable to the input terminals is positive and the capacitor is connected between the second input terminal and a potential of the output terminal when the input voltage connectable to the input terminals is negative.

Abstract: An exemplary method and an apparatus implementing the method for an arrangement having a three-phase, multi-level inverter, an output LCL-filter connecting the inverter to a grid, and a virtual-ground connection between the LCL-filter and the neutral point of the DC-link. The method includes determining a zero-sequence component of an LCL-filter inverter-side current, calculating a zero-sequence damping and balancing voltage term based on the LCL-filter inverter-side current zero-sequence component and voltages over the two halves of the DC-link, and adding the zero-sequence damping and voltage balancing term to the output voltage reference.

Abstract: A method and an apparatus for controlling a grid-connected converter which includes a boost converter, a buck converter, and a current source inverter having an output CL filter. An input of the buck converter input is connected to an output of the boost converter, and an input of the current source inverter is connected to an output of the buck converter. The method includes controlling a boost converter input voltage, controlling a boost converter output voltage through control of a buck converter output voltage, and controlling the current source inverter to produce an AC current from the buck converter output voltage. The apparatus implements the method.

Abstract: Exemplary embodiments are directed to an snubber circuit and a power converter having an active circuit. The snubber circuit includes a series connection of a first diode and a first inductor connected between a first interfacing point and a first connection point, a second diode connected between a second connection point and a second interfacing point, a series connection of a third diode and a second inductor between a third interfacing point and the second connection point, a switching device connected between the first connection point and the third interfacing point, and a first capacitor connected between the first connection point and the second connection point. The first, the second, and the third diode are forward-biased along a path between the first interfacing point and the second interfacing point and through the third interfacing point.

Abstract: Exemplary embodiments are directed to methods and systems for producing a three-phase current to a three-phase output. Switching converters are used to generate a positive current, a negative current, and an intermediate current. The system is configured such that the produced positive current follows a path of a highest phase of a sinusoidal three-phase signal at a given time, the produced negative current follows a path of a lowest phase of the three-phase signal at the given time, and the produced intermediate current follows a path of a phase of the three-phase signal between the highest and the lowest phase at the given time. The produced currents are switched to each phase conductor of the three-phase output in sequence so that phase currents of the three-phase current are formed in the output conductors.

Abstract: A phase-locked loop and method for estimating a phase angle of a three-phase reference signal is disclosed, which includes an adaptive quadrature signal generator configured to calculate an estimated first state and an estimated second state of a model of an unbalanced three-phase system at a fundamental frequency of the reference signal on a basis of the reference signal and an estimated fundamental frequency; a reference frame transformation block configured to calculate a direct component and a quadrature component in a rotating reference frame synchronous with an estimated phase angle on a basis of the fundamental positive sequence component and the estimated phase angle, and configured to determine an estimate of an amplitude of the fundamental positive sequence component on the basis of the direct component; and an estimator configured to determine estimates of the estimated fundamental frequency and the estimated phase angle on the basis of the quadrature component.

Abstract: An exemplary method and an apparatus implementing the method for an arrangement having a three-phase, multi-level inverter, an output LCL-filter connecting the inverter to a grid, and a virtual-ground connection between the LCL-filter and the neutral point of the DC-link. The method includes determining a zero-sequence component of an LCL-filter inverter-side current, calculating a zero-sequence damping and balancing voltage term based on the LCL-filter inverter-side current zero-sequence component and voltages over the two halves of the DC-link, and adding the zero-sequence damping and voltage balancing term to the output voltage reference.