A cascaded multilevel converter is disclosed. The converter comprises a plurality of modules coupled to form a branch, each of the modules comprising a switching circuit and a DC link for supplying DC voltage to the switching circuit. The converter further comprises a controller for controlling the switching circuit of each module to generate an AC voltage in the branch, wherein the controller is configured to: determine for each module a voltage across a capacitor of the DC link of the module, determine for each module a reference power value for charging the capacitor of the DC link of the module to a reference voltage value for the module, determine, from the reference power values of the modules, a common reference AC current value for AC current in the branch, determine, from the common reference AC current value, a common reference AC voltage value for AC voltage in the branch.

Systems and methods for supplying power (both active and reactive) at a medium voltage from a DCSTATCOM to an IT load without using a transformer are disclosed. The DCSTATCOM includes an energy storage device, a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and/or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique.

A static synchronous compensator includes at least one converter pole for producing a first phase of an AC voltage waveform having a fundamental cycle. The first phase of the AC voltage waveform includes alternating converter pole charging and discharging regions in each fundamental cycle. The at least one converter pole includes a plurality of cascaded H-bridge cells, each having a DC voltage source and a plurality of switches. The switches are capable of being switched to produce a plurality of switching states. There is a controller configured to control the switching states of the plurality of switches of each of the cascaded H-bridge cells based on the voltages of DC voltage sources of the H-bridge cells and on whether the AC waveform is in the converter pole charging region or the converter pole discharging region.

Systems and methods for supplying power (both active and reactive) at a medium voltage from a DCSTATCOM to an IT load without using a transformer are disclosed. The DCSTATCOM includes an energy storage device, a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and/or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique.

The present invention proposes a hybrid converter branch operating mode for a Modular Multilevel power Converter MMC with MMC cells in distinct subsets operating according to a “pulse blocked” cell operation mode with DC cell voltage increase or according to a “bypass” cell operation mode without DC cell voltage increase. Repeated cell subset assignment and corresponding alternation of cell operating mode allows to reduce or at least manage a mean deviation of the cell capacitor DC voltages of the converter cells. The invention also reduces no-load losses of the MMC in standby mode and a charging voltage in an MMC charging mode.

The present disclosure relates to a converter cell (4) for an MMC. The cell comprises a primary energy storage (C.sub.m), an inductor (Lf), and a secondary energy storage (C.sub.f); and first and second converter valves (T1, T2). The secondary energy storage (C.sub.f) is connected in series with the first converter valve (T1), and together with said first converter valve in parallel with the inductor (L.sub.f), and the primary energy storage (C.sub.m) is connected in series with the second converter valve (T2), and together with said second converter valve (T2) in parallel with the inductor (L.sub.f).

A device is for reactive power compensation in a high-voltage network having a phase conductor. The device has a first high-voltage terminal, which is configured to be connected to the phase conductor. For each first high-voltage terminal, a first and a second core section, which are part of a magnetic circuit, a first high-voltage winding, which encloses the first core section, and a second high-voltage winding are provided. Moreover, the device has a saturation switching branch, which saturates the core sections and has controllable power semiconductor switches. A control unit is used to control the power semiconductor switches. The first and the second high-voltage windings are connected by the high-voltage end to the associated first high-voltage terminal and on the low-voltage side can be connected to one or the saturation switching branch. To be able to be connected in series into the high-voltage network, a second high-voltage terminal is provided.

Systems and methods for supplying power (both active and reactive) at a medium voltage from a DCSTATCOM to an IT load without using a transformer are disclosed. The DCSTATCOM includes an energy storage device, a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and/or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique.

A converter assembly has a converter with multiple converter valves, each with a plurality of semiconductor switches, and with a stored energy source branch which is connected in parallel with at least one of the converter valves. The stored energy source branch has voltage converter modules and stored energy source modules. The voltage converter modules are connected to one another in a series circuit on the input side and to the respectively associated stored energy source module on the output side. There is also described an assembly having the stored energy source branch and a method for stabilizing an alternating current system by way of the converter assembly.

An arrangement has a converter with an electrical series circuit of modules each having four electronic switching elements and an electrical energy storage device. The arrangement also has a cooling device for cooling the electronic switching elements by way of a liquid coolant and a heat exchanger and a control unit for controlling the electronic switching elements. The control unit controls the electronic switching elements in such a manner that at least one current harmonic is generated in the series circuit if the temperature of the liquid coolant or the temperature of a medium, which is intended to absorb the heat at the heat exchanger, falls below a predetermined limit temperature.