Abstract: Pairs of phases of an AC power source are connected to pairs of phases of a motor in a first sequence that repeats at a first frequency. The motor is braked by connecting pairs of phases of the AC power source to pairs of phases of the motor in a second sequence that is reversed with respect to the first sequence and that repeats at a second frequency less than the first frequency. In further aspects, pairs of phases of an AC power source are connected to pairs of phases of a motor in a first sequence. The motor is subsequently disconnected from the AC power source for a predetermined dwell interval having a duration greater than a time constant of the motor. The motor is braked using a second sequence that is reversed with respect to the first sequence.

Abstract: A reduced voltage soft starter (RVSS) includes a switching circuit configured to selectively couple an AC power source to a motor and a control circuit configured to sense a line voltage provided to the switching circuit to produce a first voltage signal, to sense a current of the motor to generate a current signal and to generate a second voltage signal representative of a voltage of the motor responsive to the first voltage signal and the current signal. The control circuit may be further configured to generate an estimate of a torque of the motor responsive to the second voltage signal and to control the torque of the motor responsive to the torque estimate.

Abstract: An apparatus includes a plurality of DC buses and a plurality of inverter circuits, respective ones of which are coupled to respective ones of the plurality of DC buses. The apparatus further includes a control circuit configured to generate a representative DC voltage signal based on DC voltage signals for respective ones of the DC buses, to generate a first modulation control signal from the representative DC voltage signal, to generate second modulation control signals for the respective inverter circuits from the representative DC voltage signal and the first modulation control signal that are normalized based on the DC voltage signals for the buses and the representative DC voltage signal, and to modulate the inverter circuits responsive to respective ones of the second modulation control signals. The representative DC voltage signal may represent a maximum of the DC voltages for the respective DC buses.

Abstract: A converter of a variable frequency drive (VFD) is operated in a ramp-up mode to produce an AC output voltage for accelerating a motor. A loading of the converter is determined concurrent with the ramp-up mode. Transfer of the motor to a bypassed mode is conditioned on whether the determined loading in the ramp-up mode meets a criterion. In some embodiments, conditioning transfer to the bypassed mode comprises foregoing transition to the bypassed mode based on a comparison of the determined loading to an underloading threshold.

Abstract: A reduced voltage soft starter (RVSS) includes a switching circuit configured to selectively couple an AC power source to a motor and a control circuit configured to sense a line voltage provided to the switching circuit to produce a first voltage signal, to sense a current of the motor to generate a current signal and to generate a second voltage signal representative of a voltage of the motor responsive to the first voltage signal and the current signal. The control circuit may be further configured to generate an estimate of a torque of the motor responsive to the second voltage signal and to control the torque of the motor responsive to the torque estimate.

Abstract: Pairs of phases of an AC power source are connected to pairs of phases of a motor in a first sequence that repeats at a first frequency. The motor is braked by connecting pairs of phases of the AC power source to pairs of phases of the motor in a second sequence that is reversed with respect to the first sequence and that repeats at a second frequency less than the first frequency. In further aspects, pairs of phases of an AC power source are connected to pairs of phases of a motor in a first sequence. All of the phases of the motor are subsequently disconnected from the AC power source for a predetermined dwell interval having a duration greater than a time constant of the motor, and thereafter the motor is braked by connecting pairs of phases of the AC power source to pairs of phases of the motor in a second sequence that is reversed with respect to the first sequence. Motor starters implementing such operations are also disclosed.

Abstract: An apparatus, such as an adjustable frequency drive (AFD), includes an inverter configured to be selectively coupled to a motor in a first mode and an AC line in a second mode and a control circuit configured to operate the inverter as a motor drive in the first mode and as a power compensator in the second mode. The power compensator may provide power factor correction. The control circuit may include a scalar controller configured to control the inverter according to a voltage vs. frequency characteristic determined by a field weakening point reference and the control circuit may vary the field weakening point reference in the second mode. The inverter may have an input coupled to a DC bus and the control circuit may be configured to adjust a frequency of the inverter in the second mode to increase a voltage on the DC bus.

Abstract: A motor starter includes a plurality of semiconductor switches configured to couple respective phases of an AC power source to respective phases of a motor and a control circuit configured to configured to selectively operate the semiconductor switches to gradually increase a voltage applied to the motor, to determine root mean square (RMS) current values of a current of the motor as the voltage increases, and to cause the semiconductor switches to apply a full voltage or a more steeply ramping voltage to the motor responsive to the RMS current values meeting a criterion.

Abstract: An apparatus includes a first DC bus, a second DC bus a first converter circuit coupled to the first DC bus, and a second converter circuit coupled to the second DC bus. The apparatus further includes a limiter circuit coupled to the second DC bus, a first control circuit configured to sense a voltage on the first. DC bus and to responsively control the first. converter circuit to, limit the voltage on the. first ,DC bus, and a second control circuit configured to sense a voltage on the second DC bus and to responsively control the limiter circuit, to limit the voltage on the second DC bus. The apparatus may include a modulation conversion circuit configured to provide a .set of switch control signals to the converter circuits and implemented in a module that is also used to implement the second control circuit.

Abstract: An apparatus includes a first DC bus, a second DC bus, a first converter circuit coupled to the first DC bus, and a second converter circuit coupled to the second DC bus. The apparatus further includes a limiter circuit coupled to the second DC bus, a first control circuit configured to sense a voltage on the first DC bus and to responsively control the first converter circuit to limit the voltage on the first DC bus, and a second control circuit configured to sense a voltage on the second DC bus and to responsively control the limiter circuit to limit the voltage on the second DC bus. The apparatus may include a modulation conversion circuit configured to provide a set of switch control signals to the converter circuits and implemented in a module that is also used to implement the second control circuit.

Abstract: An apparatus, such as a variable frequency drive (VFD), includes a rectifier, a DC bus coupled to an output of the rectifier and at least one capacitor coupled to the DC bus. The apparatus further includes a normally-conducting switch coupled to the DC bus and configured to discharge the at least one capacitor in a conducting state and a control circuit configured to control the normally-conducting switch responsive to an input to the rectifier. The control circuit may be configured to control the normally-conducting switch responsive to a voltage at the input of the rectifier. The control circuit may include a regulator circuit having an input coupled to the input of the rectifier and a driver circuit coupled to an output of the regulator circuit and configured to drive a control terminal of the normally-conducting switch.

Abstract: An apparatus, such as an adjustable frequency drive (AFD), includes an inverter configured to be selectively coupled to a motor in a first mode and an AC line in a second mode and a control circuit configured to operate the inverter as a motor drive in the first mode and as a power compensator in the second mode. The power compensator may provide power factor correction. The control circuit may include a scalar controller configured to control the inverter according to a voltage vs. frequency characteristic determined by a field weakening point reference and the control circuit may vary the field weakening point reference in the second mode. The inverter may have an input coupled to a DC bus and the control circuit may be configured to adjust a frequency of the inverter in the second mode to increase a voltage on the DC bus.

Abstract: An apparatus, such as a variable frequency drive (VFD), includes a rectifier, a DC bus coupled to an output of the rectifier and at least one capacitor coupled to the DC bus. The apparatus further includes a normally-conducting switch coupled to the DC bus and configured to discharge the at least one capacitor in a conducting state and a control circuit configured to control the normally-conducting switch responsive to an input to the rectifier. The control circuit may be configured to control the normally-conducting switch responsive to a voltage at the input of the rectifier. The control circuit may include a regulator circuit having an input coupled to the input of the rectifier and a driver circuit coupled to an output of the regulator circuit and configured to drive a control terminal of the normally-conducting switch.

Abstract: In one embodiment, a variable frequency drive system includes a main contactor, a variable frequency drive, a charging module structured to generate a magnetizing AC voltage, wherein the charging module is structured to selectively provide the magnetizing AC voltage to a transformer of the variable frequency drive, and a sensing and control circuit having a number of sensors operably associated with the variable frequency drive. The sensing and control circuit is structured to detect a short circuit condition in the variable frequency drive when the magnetizing AC voltage is provided to the transformer based on an output of at least one of the number of sensors, and responsive thereto prevent the main contactor from being closed and thereby prevent the main AC voltage from being provided to the transformer.

Abstract: In one embodiment, a variable frequency drive system includes a main contactor, a variable frequency drive, a charging module structured to generate a magnetizing AC voltage, wherein the charging module is structured to selectively provide the magnetizing AC voltage to a transformer of the variable frequency drive, and a sensing and control circuit having a number of sensors operably associated with the variable frequency drive. The sensing and control circuit is structured to detect a short circuit condition in the variable frequency drive when the magnetizing AC voltage is provided to the transformer based on an output of at least one of the number of sensors, and responsive thereto prevent the main contactor from being closed and thereby prevent the main AC voltage from being provided to the transformer.

Abstract: A system, and associated method, for controlling a motor drive coupled to an AC power source in a condition wherein the motor drive is generating a regenerative current. The system includes a plurality of electronic switching devices structured to be provided in anti-parallel connection with a plurality of rectifier diodes of the motor drive, and a controller structured and configured to receive a number of phase voltages from the AC power source, determine a grid angle for the AC power source using the number of phase voltages, and generate a number of control signals for controlling the electronic switching devices using the grid angle when the motor drive is generating the regenerative current.

Abstract: A system, and associated method, fbr controlling a motor drive coupled to an AC power source in a condition wherein the motor drive is generating a regenerative current. The system includes a plurality of electronic switching devices structured to be provided in anti-parallel connection with a plurality of rectifier diodes of the motor drive, and a controller structured and configured to receive a number of phase voltages from the AC power source, determine a grid angle for the AC power source using the number of phase voltages, and generate a number of control signals for controlling the electronic switching devices using the grid angle when the motor drive is generating the regenerative current.