Abstract: A transformerless cycloconverter for connecting a first three-conductor system to a second three-conductor system by bridge modules with electronic semiconductor switches has precisely six bridge modules or series circuits thereof with a first bridge module or series circuit connected to the first conductors of the first and second systems, a second bridge module or series circuit connected to the second and first conductors of the first and second systems, a third bridge module or series circuit connected to the second conductors of the first and second systems, a fourth bridge module or series circuit connected to the third and second conductors of the first and second systems, a fifth bridge module or series circuit connected to the third conductors of the first and second systems, and a sixth bridge module or series circuit connected to the first and third conductors of the first and second systems.

Abstract: The invention relates to a transformerless cycloconverter for connecting a first three-conductor grid (50), in particular a three-phase grid, to a second three-conductor grid (51), in particular a three-phase grid, by means of bridge modules comprising electronic semiconductor circuits (5, 6, 7, 8), having the following characteristics: a) a first bridge module (1) or a first series circuit (52) of bridge modules (1) is connected to a first conductor (500) of the first power supply grid (50) and to a first conductor (510) of the second power supply grid (51), b) a on one side and to a first conductor (510) of the second power supply grid (51) on the other side, b) a second bridge module (1) or a second series circuit (53) of bridge modules (1) is connected to a second conductor (501) of the first power supply grid (50) and to the on one side and to the first conductor (510) of the second power supply grid (50), c) a conductor (510) of the second power supply grid (51) on the other side, c) a third bridge modu

Abstract: The invention relates to a method for detecting a rotating stall fault in a compressor (12) which is driven by means of a three-phase current motor (8) fed by an inverter. According to the invention, an instantaneous estimated value (^m) which is calculated from measured power converter output currents (iS1, iS2, iS3) and a measured rotational-speed-proportional signal (?) is compared with an instantaneous setpoint value (m*) determined from a measured rotational-speed-proportional signal (?) and a predetermined rotational-speed-proportional signal (?*), in such a way that in the case of inequality a signal (SRS) is generated which indicates that the rotating stall fault has occurred. In this way, it is possible for the rotating stall fault to be detected without pressure sensors and/or oscillation pickups in a compressor (12) which is driven with a three-phase current motor (8) fed by inverter.

Abstract: A method for operation of a compressor supplied by a power converter having an operating condition (BV) for the compressor (12) supplied by a power converter, generated from a measured actual rotational speed (n) of the compressor and a given effective current component (iW) of a measured power converter output current (I) using a stored speed-dependent pump characteristic curve (SG) monitored for validity such that on determining invalidity, as per a stored speed-dependent instantaneous curve, a control signal (SSG) for reducing a torque (M) is generated. A method for operation of a compressor supplied by a power converter is then achieved with which the duration and the intensity of surge conditions is significantly reduced.

Abstract: The invention relates to a method for detecting a rotating stall fault in a compressor (12) which is driven by means of a three-phase current motor (8) fed by an inverter. According to the invention, an instantaneous estimated value (?m) which is calculated from measured power converter output currents (iS1, iS2, iS3) and a measured rotational-speed-proportional signal (?) is compared with an instantaneous setpoint value (m*) determined from a measured rotational-speed-proportional signal (?) and a predetermined rotational-speed-proportional signal (?*), in such a way that in the case of inequality a signal (SRS) is generated which indicates that the rotating stall fault has occurred. In this way, it is possible for the rotating stall fault to be detected without pressure sensors and/or oscillation pickups in a compressor (12) which is driven with a three-phase current motor (8) fed by inverter.

Abstract: The invention relates to a method for operation of a compressor supplied by a power converter. According to the invention, an operating condition (BV) for the compressor (12) supplied by a power converter, generated from a measured actual rotational speed (n) of the compressor and a given effective current component (iW) of a measured power converter output current (I) by means of a stored speed-dependent pump characteristic curve (SG) is monitored for validity such that on determining invalidity, as per a stored speed-dependent instantaneous curve, a control signal (SSG) for reducing a torque (M) is generated. A method for operation of a compressor supplied by a power converter is thus achieved with which the duration and the intensity of surge conditions is significantly reduced.

Abstract: A low-loss power inverter is provided. Each inverter phase includes an upper and a lower bridge half, each having two power semiconductor switches, with antiparallel-connected diodes, with one tie point of the power semiconductor switches being connected using an isolating diode to a tie point of a d.c. intermediate circuit, an auxiliary circuit consisting of an upper and a lower auxiliary switch and a resonant inductor is provided, and at least one resonant capacitor is provided for power semiconductor switches of the inverter phase. This yields a low-loss power inverter which combines the advantages of a three-point inverter with those of an ARCP inverter.