A threshold detection system can be configured to monitor a location (e.g., a DC link) for overcurrent. The threshold detection system can be configured to generate a pulse width modulated signal with a duty cycle that is proportional to current through the DC link. The threshold detection system can be configured to determine whether the duty cycle exceeds a selected threshold.

A power converting system includes a power converting device, a protection device, and a charging device. The power converting device is coupled to a first and a second power source. The protection device is coupled to the power converting device, a load, and a grid, and switches electrical connections among the power converting device, the load, and the grid. The charging device is coupled to the power converting device and a third power source. The power converting device charges the third power source through the charging device, or receives electricity through the charging device. Select at least one power source of the first power source, the second power source, the third power source and the grid to provide electricity to the load according to multiple preset modes.

A system for protecting a vehicle inverter from overvoltage includes a first inverter having switching elements and converting energy from an energy storage device into AC power. A first motor is driven by receiving the converted AC power. A second inverter is connected in parallel with the first inverter, includes a switching elements, and converts energy from the energy storage device into AC power. A second motor is driven by receiving the converted AC power. A first capacitor is connected in parallel between the first inverter and the energy storage device and stores electric energy of the first motor during regenerative braking. A controller turns off a relay connecting the energy storage device and the motor when a voltage of the first capacitor is equal to or greater than a predetermined voltage and operates the switching elements in the inverters in response to first and second current commands.

A system for protecting a vehicle inverter from overvoltage includes a first inverter having switching elements and converting energy from an energy storage device into AC power. A first motor is driven by receiving the converted AC power. A second inverter is connected in parallel with the first inverter, includes a switching elements, and converts energy from the energy storage device into AC power. A second motor is driven by receiving the converted AC power. A first capacitor is connected in parallel between the first inverter and the energy storage device and stores electric energy of the first motor during regenerative braking. A controller turns off a relay connecting the energy storage device and the motor when a voltage of the first capacitor is equal to or greater than a predetermined voltage and operates the switching elements in the inverters in response to first and second current commands.

A modular multilevel converter includes a plurality of submodules, each having at least two electronic switching elements, an electric energy store, two submodule connections, a bypass switch bridging the submodule, and a communication element communicating with a communication apparatus. A method for operating the modular multilevel converter includes ascertaining that the submodules have a defective submodule so that the communication element in the defective submodule does not communicate with the communication apparatus, determining whether a present arm current resulting from an operating point of the modular multilevel converter is below a predetermined threshold value, and generating or amplifying a converter-internal circular current with the defective submodule if the arm current resulting from the operating point is below the predetermined threshold value. A modular multilevel converter is also provided.

An adaptive electrical power distribution panel receives electrical power from at least an alternative power source other than a utility electric grid, and selectively outputs power to a plurality of branch circuits, appliances, or devices. An internal or remote controller monitors conditions. In response to the monitored conditions, the controller algorithmically divides the plurality of branch circuits, appliances, or devices into a first group to receive power from the alternative power source and a second group to not receive power from the alternative power source, and breaks electrical connections between the alternative power source and the second group. The monitored conditions may include operating parameters the grid; an instantaneous or average individual current flow; and a charge state of storage batteries. The division into groups may also be in response to stored information, such as a priority of, or history of current usage by, each branch circuit, appliance, or device.

A medium-voltage grid-connected photovoltaic inverter system includes: a photovoltaic inverter, a medium-voltage transformer, a medium-voltage switch, and an inverter grid-connected controller. A direct current input terminal of the photovoltaic inverter is connected to a direct current bus. A low-voltage side of the medium-voltage transformer is connected to an alternating current output terminal of the photovoltaic inverter. An input terminal of the medium-voltage switch is connected to a high-voltage side of the medium-voltage transformer, and an output terminal of the medium-voltage switch is configured to be connected to a medium-voltage grid. A current sensor is integrated in the medium-voltage switch to detect a grid-connected current of the photovoltaic inverter system and output a current detection signal.

A medium-voltage grid-connected photovoltaic inverter system includes: a photovoltaic inverter, a medium-voltage transformer, a medium-voltage switch, and an inverter grid-connected controller. A direct current input terminal of the photovoltaic inverter is connected to a direct current bus. A low-voltage side of the medium-voltage transformer is connected to an alternating current output terminal of the photovoltaic inverter. An input terminal of the medium-voltage switch is connected to a high-voltage side of the medium-voltage transformer, and an output terminal of the medium-voltage switch is configured to be connected to a medium-voltage grid. A current sensor is integrated in the medium-voltage switch to detect a grid-connected current of the photovoltaic inverter system and output a current detection signal.

In a multilayer printed circuit board (circuit board 20) having an inverter (switching elements 22) mounted thereto, only a second wiring pattern P2 arranged downstream of a semiconductor relays 24 and able to shut off an electric power supply and a third wiring pattern P3 arranged upstream of a shunt resistor 27 and able to detect an overcurrent are placed in adjacent layers in a manner to face each other, and thus, even if the mutually facing portions (laminated portion) of the these two wiring patterns P2 and P3 are subjected to short circuit, an overcurrent caused by the short circuit can be detected by the shunt resistor 27 and the electric power supply to the switching elements 22 can be shut off by the switching elements 22, so that overheating at the second and third wiring patterns P2 and P3 can be avoided.

In a multilayer printed circuit board (circuit board 20) having an inverter (switching elements 22) mounted thereto, only a second wiring pattern P2 arranged downstream of a semiconductor relays 24 and able to shut off an electric power supply and a third wiring pattern P3 arranged upstream of a shunt resistor 27 and able to detect an overcurrent are placed in adjacent layers in a manner to face each other, and thus, even if the mutually facing portions (laminated portion) of the these two wiring patterns P2 and P3 are subjected to short circuit, an overcurrent caused by the short circuit can be detected by the shunt resistor 27 and the electric power supply to the switching elements 22 can be shut off by the switching elements 22, so that overheating at the second and third wiring patterns P2 and P3 can be avoided.