Examples of the disclosure include a UPS comprising an output to be coupled to a load, a first converter leg to provide a first voltage to the output and including at least one of a first relay or fuse, a second converter leg in parallel with the first converter leg including at least one of a second relay or fuse and configured to provide a second voltage to the output out of phase with the first converter leg providing the first voltage signal, current sensors coupled to the first and second converter legs, respectively, and configured to provide a first signal indicative of a current in the first converter leg and a second signal indicative of a current in the second converter leg, respectively, and at least one controller to receive the signals, determine a current difference between the converter legs based on the signals, and decrease the current difference.

An inverter circuit includes a plurality of flying capacitors and converts a DC voltage supplied from a DC power supply into an AC voltage. A filter circuit approximates a waveform of an output voltage of the inverter circuit to a sinusoidal wave. An excess current protection circuit supplies a block signal for turning off a plurality of switching elements to the driving circuit when an excess current is detected. When at least one of an abnormal voltage in any of the plurality of flying capacitors and an abrupt change in an output voltage of the power converter occurs, voltages other than a positive voltage of the DC power supply, a negative voltage of the DC power supply, and a zero voltage are restricted from being output from the inverter circuit.

An inverter circuit includes a plurality of flying capacitors and converts a DC voltage supplied from a DC power supply into an AC voltage. A filter circuit approximates a waveform of an output voltage of the inverter circuit to a sinusoidal wave. An excess current protection circuit supplies a block signal for turning off a plurality of switching elements to the driving circuit when an excess current is detected. When at least one of an abnormal voltage in any of the plurality of flying capacitors and an abrupt change in an output voltage of the power converter occurs, voltages other than a positive voltage of the DC power supply, a negative voltage of the DC power supply, and a zero voltage are restricted from being output from the inverter circuit.

In an embodiment a power converter includes a first capacitor and a second capacitor coupled in series with the first capacitor, wherein the converter is configured to charge, during a first phase, the first and second capacitors by a supply voltage so that a voltage across terminals of each of the first and second capacitors is substantially equal to half the supply voltage and discharge, during a second phase, the second capacitor to a third capacitor.

A method provides current limitation in the event of transient voltage variations at an AC output of a multilevel inverter that includes a bridge circuit with a first DC input, a second DC input, a neutral terminal and a bridge output, as well as a line filter with a choke connected between the bridge output and the AC output, and a capacitor connected between the AC output and the neutral terminal. In the method, depending on the voltage at the capacitor, when a first current threshold is exceeded by the choke current, a regular operating mode is interrupted and measures for current limitation are initiated. A multilevel inverter is further disclosed including a control circuit that is configured to carry out such a method.

A method provides current limitation in the event of transient voltage variations at an AC output of a multilevel inverter that includes a bridge circuit with a first DC input, a second DC input, a neutral terminal and a bridge output, as well as a line filter with a choke connected between the bridge output and the AC output, and a capacitor connected between the AC output and the neutral terminal. In the method, depending on the voltage at the capacitor, when a first current threshold is exceeded by the choke current, a regular operating mode is interrupted and measures for current limitation are initiated. A multilevel inverter is further disclosed including a control circuit that is configured to carry out such a method.

In the field of high voltage direct current (HVDC) power transmission networks there is a need for an improved power converter. A power converter, for use in a HVDC power transmission network, comprises first and second DC terminals, for connection in use to a DC network and between which extends at least one converter limb. The or each converter limb includes first and second limb portions which are separated by an AC terminal, for connection in use to an AC network. Each limb portion includes a switching valve, and the power converter including a controller programmed to control switching of the switching valves to control the flow of a converter current (I.sub.max) through the power converter and thereby in-use transfer power between the power converter and the AC network. The power transferred between the power converter and the AC network has an active component and a reactive component. The controller is further programmed in use to: (i) prioritize to a first extent the transfer of reactive power between the power converter and the AC network during a first operating condition, when the AC voltage (V) of the AC network lies outside a desired operating range, by allowing up to a first amount of the converter current (I.sub.max) to be a reactive current; and (ii) prioritize to a second extent, less than the first extent, the transfer of reactive power between the power converter and the AC network during a second operating condition, when the AC voltage (V) of the AC network lies within the desired operating range, by limiting the amount of converter current (I.sub.max) that can be a reactive current to a second amount, less than the first amount, the second amount being determined according to a measured operating frequency of the AC network.

The present disclosure relates to a voltage source converter (VSC) (300) comprising: a first MOSFET switching element (302) including a first body diode (306); a second MOSFET switching element (304) including a second body diode (308), the second MOSFET switching element (304) being connected in series with the first MOSFET switching element (302); a protection device (318) connected in parallel with the second MOSFET switching element (304); and a controller (312), wherein the controller (312) is configured, on detection of an overcurrent event, to: switch off the first MOSFET switching element (302); and switch off the second MOSFET switching element (304), thereby forcing current flowing in the VSC (300) following the overcurrent event to flow through the second body diode (308) rather than through conducting channels of the first and second MOSFET switching elements (302, 304).

The present disclosure relates to a sub-module of a power converter, the sub-module capable of allowing failure-causing electric current to bypass the sub-module when a failure occurs in the sub-module. According to an embodiment of the present disclosure, there is proposed a sub-module of a power converter, the sub-module including an energy storage unit, at least one power semiconductor circuit connected, in parallel, to the energy storage unit and configured with a plurality of power semiconductor switches and a plurality of freewheeling diodes, an auxiliary switching element connected to the energy storage unit, turned on when a failure occurs, and thus allowing electric current from the energy storage unit to pass through, and a main switching element connected in series to an output terminal of the auxiliary switching element, arranged between two output terminals connected to one of one or more of the power semiconductor circuits, forced to undergo an induced failure due to application of a voltage stored in the energy storage unit through the auxiliary switching element, internally short-circuited, and thus connecting the output terminals to each other.

A common-mode voltage injection control method and apparatus for an inverter. For the method and apparatus, a common-mode voltage for a DPWM mode is calculated based on three-phase port voltages and an output power command; a common-mode voltage for an MPC modulation mode is calculated based on the direct current bus voltage, the three-phase port voltages, and the output power command; a modulation proportion is determined based on a maximum phase voltage peak value of the three-phase port voltages, the direct current bus voltage, and a power factor of the output power command; and a common-mode injection voltage is generated based on the common-mode voltage for the DPWM mode, the modulation proportion, and the common-mode voltage for the MPC modulation mode.