Abstract: A first MOS transistor of a specific conductive type and a second MOS transistor of the specific conductive type are combined in an electrostatic circuit protection. In the first MOS transistor, a drain thereof is connected to an output terminal or an input terminal and a source thereof is connected to a first power terminal. The first MOS transistor is turned on/off by a signal received by a gate or ordinarily turned off by holding the gate at a specific potential. In the second MOS transistor of the specific conductive type, a drain thereof is connected to the output terminal or the input terminal and a source thereof is connected to a gate of the first MOS transistor. The second MOS transistor is ordinarily turned off by connecting a gate thereof to the first power terminal.

Abstract: A plant for transmitting electric power between a direct voltage network and an alternating voltage network through a power station. A converter of a station has two current valves connected in series, each having one turn-on and turn-off type breaker and a diode connected anti-parallel therewith. Circuits are provided to detect the direction and the intensity of the current through the converter, as well as the current valve through which it flows to actuate the control apparatus on the basis of the detected current level and the identity of the valve carrying the current. The control apparatus operates to commutate current through the valve which is not carrying current when a detected current level in the current carrying valve exceeds a first predetermined level.

Abstract: A system for transmitting power over a direct voltage network. A first power station connects one alternating voltage network to the direct voltage network. The first power station includes a converter for bidirectionally transferring power between the direct voltage network and the alternating voltage network. The converter maintains constant value of voltage on the network, or operates in a second alternative mode of controlling constant current between the alternating voltage network and the direct voltage network. When the voltage on the direct voltage network drops below a reference value, a second power station connected to the direct voltage network and to a remaining alternating voltage network takes over the voltage regulation function. The second power station prior to taking over the voltage regulating friction was in a current regulating function.

Abstract: A device for converting direct voltage into a three phase alternating voltage having a two level converter connected to a direct voltage network and to an alternating voltage network. A control apparatus for performing pulse width modulation determines the pulse width modulation pattern for each phase by comparing a triangular wave for each phase with a reference alternating voltage. The triangular wave is inverted an even number of times during a fundamental oscillation of the reference alternating voltage and the time position of the inversions of each triangular wave is always such that two triangular waves are half a period displaced with respect to the third.