Abstract: In an induction motor group control system, magnetic energy recovery switches (3) are connected in series to an induction motor (2) directly driven by a commercial power supply, and a plurality of induction motor control devices (10) enabling voltage control and reactive power control of the induction motor 2 are employed to control generation of reactive power so as to maximize a power factor of the entire plurality of AC loads including the induction motor or compensate variations in voltage of an AC power supply (1).

Abstract: This invention provides a steel pipe material weld zone heating method and apparatus for melting and welding the weld zone of a steel pipe material that during continuous induction heating and welding of moving steel pipe material as the material being heated controls temperature distribution and molten steel shape and weld frequency fluctuation with high accuracy and high efficiency, irrespective of the shape of the heated region of material being heated or the material properties of the material being heated, which comprises a first imaging device, a weld zone temperature distribution computation device, a heating control device, and a variable frequency alternating current power supply device.

Abstract: A protected power conversion device (1) includes a full-bridge MERS (100), a control circuit (200), and an ammeter (300), and is connected between a DC current source (2) and an inductive load (3). The ammeter (300) measures a current value supplied to the inductive load (3). The control circuit (200) changes the states of four reverse-conductive semiconductor switches (SW1) to (SW4) configuring the full-bridge MERS (100) to convert power output by the DC current source (2) into AC power, and supplies the AC power to the inductive load (3). When, for example, the inductive load (3) is short-circuited and malfunctions, a large current flows therethrough, and the current value detected by the ammeter (300) becomes equal to or greater than a predetermined value, the control circuit (200) turns OFF all reverse-conductive semiconductor switches (SW1) to (SW4) to cut OFF the large current.

Abstract: A power inverter (1) is provided with a full-bridge circuit (10), a shunt capacitor (CP), and a control circuit (20). The control circuit (20) controls the on/off state of each reverse-conductive semiconductor switch (SW1 to SW4) at a switching frequency of not more than the resonance frequency determined by the capacitance of the shunt capacitor (CP) and the inductance of an inductive load (LD) in such a matter than when a first reverse-conductive semiconductor switch (SW1) and a fourth reverse-conductive semiconductor switch (SW4) are in the on-state, a second reverse-conductive semiconductor switch (SW2) and a third reverse-conductive semiconductor switch (SW3) are brought into the off-state, and that when the first reverse-conductive semiconductor switch (SW1) and the fourth reverse-conductive semiconductor switch (SW4) are in the off-state, the second reverse-conductive semiconductor switch (SW2) and the third reverse-conductive semiconductor switch (SW3) are brought into the on-state.

Abstract: In an induction motor group control system, magnetic energy recovery switches (3) are connected in series to an induction motor (2) directly driven by a commercial power supply, and a plurality of induction motor control devices (10) enabling voltage control and reactive power control of the induction motor 2 are employed to control generation of reactive power so as to maximize a power factor of the entire plurality of AC loads including the induction motor or compensate variations in voltage of an AC power supply (1).

Abstract: Reverse conducting type semiconductor switches are arranged in a bride from, an energy storage capacitor is connected with its DC terminal to obtain a magnetic energy regeneration switch, and then an induction coil is connected to its AC terminal. An AC pulse current of variable frequency is obtained by applying a gate signal to the semiconductor switch to thereby turn it ON/OFF; since a voltage is generated automatically by regenerating magnetic energy, a DC power supply is connected to the opposite ends of the capacitor through a smoothing coil, thus injecting power.

Abstract: This invention provides a steel pipe material weld zone heating method and apparatus for melting and welding the weld zone of a steel pipe material that during continuous induction heating and welding of moving steel pipe material as the material being heated controls temperature distribution and molten steel shape and weld frequency fluctuation with high accuracy and high efficiency, irrespective of the shape of the heated region of material being heated or the material properties of the material being heated, which comprises a first imaging step in which first imaging means 3 installed opposite an end face weld zone of the steel pipe material is used to detect self-emitted light of the weld zone and output a brightness image, a weld zone temperature distribution computation step in which image processing is performed based on the brightness image and emitted light temperature measurement is applied to compute the plate-thickness direction temperature distribution of the weld zone, a heating control step in

Abstract: Reverse conducting type semiconductor switches are arranged in a bride from, an energy storage capacitor is connected with its DC terminal to obtain a magnetic energy regeneration switch, and then an induction coil is connected to its AC terminal. An AC pulse current of variable frequency is obtained by applying a gate signal to the semiconductor switch to thereby turn it ON/OFF; since a voltage is generated automatically by regenerating magnetic energy, a DC power supply is connected to the opposite ends of the capacitor through a smoothing coil, thus injecting power.

Abstract: A power converting apparatus comprises self-commutated converter, fault current restricting device, fault detector, and cutoff circuit. Self-commutated converter converts AC power supplied from an AC power system into DC power and supplying the DC power to a common DC circuit, and for converting DC power supplied from the DC circuit into AC power and supplying the AC power to the AC power system. The fault current restricting device is inserted between the self-commutated converted and the DC circuit, and includes a diode provided to permit a DC circuit current to flow from the self-commutated coverter to the DC circuit, and a series circuit having a reactor and a DC power supply and connected in parallel to the diode. The fault detector detects a fault current generated when self-commutated converter is short-circuited. When the fault detector detects a short circuit occurring in self-commutated converter, the cutoff circuit cuts off power supply to that self-commutated converter.