A semiconductor switching circuit includes a main current branch which includes at least one main semiconductor switching element and through which current flows in a first direction when the or each main semiconductor switching element is switched on. The semiconductor switching circuit also includes an auxiliary current branch that is connected in parallel with the main current branch. The auxiliary current branch includes at least one auxiliary semiconductor switching element. One or more control units are configured to switch on the or each auxiliary semiconductor switching element as the or each main semiconductor switching element is switched on to selectively create an alternative current path via the auxiliary current branch whereby current flowing in the first direction through the main current branch is diverted instead to flow through the alternative current path to reduce the rate of change of current flowing through the or each main semiconductor switching element.

A semiconductor switching circuit includes a main current branch which includes at least one main semiconductor switching element and through which current flows in a first direction when the or each main semiconductor switching element is switched on. The semiconductor switching circuit also includes an auxiliary current branch that is connected in parallel with the main current branch. The auxiliary current branch includes at least one auxiliary semiconductor switching element. One or more control units are configured to switch on the or each auxiliary semiconductor switching element as the or each main semiconductor switching element is switched on to selectively create an alternative current path via the auxiliary current branch whereby current flowing in the first direction through the main current branch is diverted instead to flow through the alternative current path to reduce the rate of change of current flowing through the or each main semiconductor switching element.

A voltage source converter includes a converter limb having limb portions separated by an AC terminal and extending between DC terminals, each limb portion including a primary switching element to switch the limb portion into and out of circuit. The converter further includes an auxiliary limb. The primary switching element of each limb portion is switchable to switch the auxiliary limb into and out of circuit with the corresponding limb portion. The converter further includes a control unit to, in one mode, inject a circulation current that flows in one direction in one of the limb portions and minimize a current flowing in the opposite direction in that limb portion. Each primary switching element switches the respective limb portion into or out of circuit following the minimization of the limb portion current by the circulation current.

A voltage source converter includes a converter limb having limb portions separated by an AC terminal and extending between DC terminals, each limb portion including a primary switching element to switch the limb portion into and out of circuit. The converter further includes an auxiliary limb. The primary switching element of each limb portion is switchable to switch the auxiliary limb into and out of circuit with the corresponding limb portion. The converter further includes a control unit to, in one mode, inject a circulation current that flows in one direction in one of the limb portions and minimize a current flowing in the opposite direction in that limb portion. Each primary switching element switches the respective limb portion into or out of circuit following the minimization of the limb portion current by the circulation current.

An electric power retention distribution cell apparatus and method of operation of the cell includes a rechargeable battery assembly, a bi-directional inverter and a switch control operatively connectable to an electric utility grid, an outside power charging supply and at least one end user wherein the cell is selectively switched between the electric utility grid and the battery assembly to supply electric power to the one or more end users. The cell is connected to the power charging supply for charging the battery assembly, and for dividing the battery assembly into groups of batteries for storage at a lower terminal output voltages of each group than the battery assembly output voltage when in use as the primary power supply. Electric power supply networks are also described for a utility hub network formed using two or more cells, and for a regional utility hub network formed using multiple utility hubs.

An electric power retention distribution cell apparatus and method of operation of the cell includes a rechargeable battery assembly, a bi-directional inverter and a switch control operatively connectable to an electric utility grid, an outside power charging supply and at least one end user wherein the cell is selectively switched between the electric utility grid and the battery assembly to supply electric power to the one or more end users. The cell is connected to the power charging supply for charging the battery assembly, and for dividing the battery assembly into groups of batteries for storage at a lower terminal output voltages of each group than the battery assembly output voltage when in use as the primary power supply. Electric power supply networks are also described for a utility hub network formed using two or more cells, and for a regional utility hub network formed using multiple utility hubs.

A photovoltaic system has a plurality of subsystems, each with a photovoltaic generator and an associated inverter. The inverter has a control element for setting the maximum power point of its subsystem. A battery is connectible in parallel with the photovoltaic generator. The inverters are connectible to a power grid, which is operated by a utility operator. When a control device receives an emergency signal from the utility operator indicating impending instability of the grid, the following is initiated: If the battery voltage is above the current voltage as set by the MPP control element, the battery is immediately connected to the input of the inverter while the generator remains connected to the inverter. If the battery voltage is below the current voltage the battery connection is delayed until the MPP control element has adjusted the voltage. Then the voltage is further lowered to generate a discharge current from the battery.

A photovoltaic system has a plurality of subsystems, each with a photovoltaic generator and an associated inverter. The inverter has a control element for setting the maximum power point of its subsystem. A battery is connectible in parallel with the photovoltaic generator. The inverters are connectible to a power grid, which is operated by a utility operator. When a control device receives an emergency signal from the utility operator indicating impending instability of the grid, the following is initiated: If the battery voltage is above the current voltage as set by the MPP control element, the battery is immediately connected to the input of the inverter while the generator remains connected to the inverter. If the battery voltage is below the current voltage the battery connection is delayed until the MPP control element has adjusted the voltage. Then the voltage is further lowered to generate a discharge current from the battery.

Phase differences between primary-side series-connected first and second arms and secondary-side series-connected fifth and sixth arms and between primary-side series-connected third and fourth arms and secondary-side series-connected seventh and eighth arms are controlled for power being transmitted from the secondary side to the primary side. Turn-off of the fifth arm is corrected to cause an integrating result of a secondary coil current for an interval delayed by a current sensor response delay from an interval between turn-off of the first arm and turn-on of the seventh arm to approach zero, or turn-off of the seventh arm is corrected to cause an integrating result of the secondary coil current for an interval delayed by the response delay from an interval between turn-off of the third arm and turn-on of the fifth arm to approach zero.

An energy distribution system is provided that includes a first AC bus; a second AC bus for connecting to at least one second AC load; a third AC bus for connecting to a supply network; a transformer that converts an alternating voltage of each of the first to third AC buses into an alternating voltage of each of the other of the first to third AC buses; a DC bus; an energy storage device connected to the DC bus; and a bidirectional AC-DC power converter that is connected between the first AC bus and the DC bus.