The embodiments of the present invention provide a control system and method for a medium-voltage photovoltaic distribution system. The medium-voltage photovoltaic distribution system includes N photovoltaic modules, N DC-DC converters, a DC-AC converter and a line-frequency transformer. Outputs of the N DC-DC converters are connected in parallel to a DC bus. The DC bus is connected to the DC-AC converter. The line-frequency transformer is configured to connect to a medium-voltage AC grid. The control system includes a bus voltage sampling circuit and N DC-DC converter control circuits corresponding to the N DC-DC converters respectively. Each DC-DC converter control circuit includes a bus voltage sampling circuit, a photovoltaic sampling circuit, a droop controller, a maximum power point tracking controller, an input voltage loop regulator and a pulse width modulation wave generating circuit. It can greatly simplify the communication system and improve the reliability of the control system that the DC bus voltage is used to replace a signal line for communication.

A fault-responsive power system and method using active line current balancing. First and second supply-side currents flowing from at least one power supply and into first and second conductor pairs, respectively, are measured. First and second remote-side currents flowing from the first and second conductor pairs and into first and second power converters, respectively, are measured. The outputs of the first and second power converters are electrically coupled together in parallel and deliver power to a load. The first and second remote-side currents are balanced in response to measurements of the first and second remote-side currents while power is being delivered. When a difference between the first and second supply-side currents at least meets a magnitude threshold, the first and second supply-side currents are reduced until the difference is less than the magnitude threshold.

The present disclosure relates to a STATCOM arrangement (1) comprising an MMC (2) and a transformer arrangement (3) arranged to be an interface between the MMC (2) and an AC grid. The MMC (2) is connected in a wye topology with a plurality of converter arms, one for each phase of the AC grid, each arm comprising a plurality of chain-linked converter cells. The transformer arrangement (3) is arranged to interface each of the arms of the MMC (2) with a respective phase of the grid, and arranged to for each of the converter arms produce leakage reactance resulting in reactance in series with the arm which obviates the need for a phase reactor connected in series with said arm.

Systems and methods of the present disclosure involve passive, hybrid, and active filtering configurations to mitigate current harmonics for various electrical loads. One hybrid filtering configuration is medium voltage (MV) active filtering using a DC-DC converter and a multi-level inverter, and low voltage (LV) passive filtering. Another hybrid filtering configuration is MV passive filtering and LV active filtering using a two-level inverter. An active filtering configuration includes both MV and LV active filtering. The present disclosure also features power distribution unit (PDU) transformers electrically coupled to respective power supplies on the LV side of an electrical system. Each PDU transformer includes primary coils in a delta configuration and secondary coils in a wye configuration. The secondary coils are in series with respective leakage inductance coils. The secondary coils and the leakage inductance coils are integrated together into a single unit or module.

A power control system includes: a first AC/DC converter; a second AC/DC converter; a first switch connected between a first transmission line of a first power system having a first system frequency and the first AC/DC converter; a second switch connected between the first transmission line and the second AC/DC converter; a third switch connected between a second transmission line of a second power system having a second system frequency and the first AC/DC converter; a fourth switch connected between the second transmission line and the second AC/DC converter; a fifth switch connected between the first AC/DC converter and the second AC/DC converter; and a control device. When the first and second AC/DC converters are caused to operate as AC/DC converters in a BTB (Back to Back) method, the control device controls at least the fifth switch to be in a closed state.

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 STATCOM arrangement includes an MMC and a transformer arrangement arranged to be an interface between the MMC and an AC grid. The MMC is connected in a wye topology with a plurality of converter arms, one for each phase of the AC grid, each arm including a plurality of chain-linked converter cells. The transformer arrangement is arranged to interface each of the arms of the MMC with a respective phase of the grid, and arranged to for each of the converter arms produce leakage reactance resulting in reactance in series with the arm which obviates the need for a phase reactor connected in series with said arm.

The embodiments of the present invention provide a control system and method for a medium-voltage photovoltaic distribution system. The medium-voltage photovoltaic distribution system includes N photovoltaic modules, N DC-DC converters, a DC-AC converter and a line-frequency transformer. Outputs of the N DC-DC converters are connected in parallel to a DC bus. The DC bus is connected to the DC-AC converter. The line-frequency transformer is configured to connect to a medium-voltage AC grid. The control system includes a bus voltage sampling circuit and N DC-DC converter control circuits corresponding to the N DC-DC converters respectively. Each DC-DC converter control circuit includes a bus voltage sampling circuit, a photovoltaic sampling circuit, a droop controller, a maximum power point tracking controller, an input voltage loop regulator and a pulse width modulation wave generating circuit. It can greatly simplify the communication system and improve the reliability of the control system that the DC bus voltage is used to replace a signal line for communication.

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).

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.