Abstract: A system and method for detecting high resistance ground faults in a power distribution system is disclosed. A fault detection and protection system is provided that includes a plurality of current sensors to measure current on the three phase output of the converter-inverter arrangement of the power distribution system and a controller configured to measure the three phase current on the three phase output, extract a fundamental current component for each phase of the three phase output, extract a third harmonic component for each phase of the three phase output, compare the fundamental current component and the third harmonic component extracted from each phase to a first threshold and a second threshold, respectively, and detect a ground fault on a phase of the three phase output based on the comparisons of the fundamental current component and the third harmonic component to the first and second thresholds.

Abstract: A three-phase resonant cyclo-converter including a closed loop control module for controlling the switching frequency of the cyclo-converter, the closed loop control module including: a voltage signal development module arranged to develop a voltage signal representative of a voltage output waveform of the cyclo-converter, a storage module arranged to accumulate voltage signal values for phase portions of the voltage output waveform, where the voltage signal values are based on a voltage error signal and accumulated historical voltage signal values for the same corresponding phase portions, and a switching frequency control module arranged to develop a switching frequency control signal to control the switching frequency of the cyclo-converter based on the accumulated voltage signal values for corresponding phase portions of the voltage output waveform, and a proportional voltage signal based on a difference between the developed voltage signal and a reference voltage signal.

Abstract: A system and method for determining a rotor time constant of an AC induction machine is disclosed. During operation of the induction motor, a flux signal is injected into a rotor flux command so as to generate a time-variant rotor flux. A voltage-current flux observer determines amplitudes of rotor flux variations resulting from the time-variant rotor flux, with the amplitudes of the rotor flux variations comprising an amplitude of a rotor flux variation based on a current model of the voltage-current flux observer and an amplitude of a rotor flux variation based on a combined voltage-current model of the voltage-current flux observer. A rotor time constant of the induction motor is then estimated based on the determined amplitudes of the rotor flux variations.

Abstract: A system and method for controlling an adjustable speed drive (ASD) to decelerate an AC load during a generating mode of operation is disclosed. The ASD includes a capacitor and an inverter coupled to a DC link. A current sensor system is coupled to an output of the inverter. The ASD further includes a control system programmed to calculate an energy of the capacitor, generate a reference power using the calculated capacitor energy, and calculate a feedback power from realtime current signals received from the current sensor system. The control system compares the feedback power to the reference power, defines a frequency offset based on the comparison, generates a speed command using the frequency offset, and outputs the speed command to the inverter to maintain a smooth DC link voltage during deceleration.

Abstract: A system for identifying magnetizing inductance and rotor resistance of an induction machine comprises an induction machine comprising a rotor and a stator, a DC voltage bus, and a DC-to-AC voltage inverter coupled to the DC voltage bus and to the induction machine. The system also comprises a controller configured to cause the DC-to-AC voltage inverter to apply a square-wave excitation to a plurality of phases of the induction machine, determine a stator resistance of the stator of the induction machine based on the square-wave excitation, and determine a rotor resistance of the rotor of the induction machine based on the square-wave excitation. The controller is also configured to calculate a magnetizing curve for the induction machine based on the stator and rotor resistances and control the induction machine to operate based on the magnetizing curve.

Abstract: A system and method for determining a rotor time constant of an AC induction machine is disclosed. During operation of the induction motor, a flux signal is injected into a rotor flux command so as to generate a time-variant rotor flux. A voltage-current flux observer determines amplitudes of rotor flux variations resulting from the time-variant rotor flux, with the amplitudes of the rotor flux variations comprising an amplitude of a rotor flux variation based on a current model of the voltage-current flux observer and an amplitude of a rotor flux variation based on a combined voltage-current model of the voltage-current flux observer. A rotor time constant of the induction motor is then estimated based on the determined amplitudes of the rotor flux variations.

Abstract: A system and method for controlling an adjustable speed drive (ASD) to decelerate an AC load during a generating mode of operation is disclosed. The ASD includes a capacitor and an inverter coupled to a DC link. A current sensor system is coupled to an output of the inverter. The ASD further includes a control system programmed to calculate an energy of the capacitor, generate a reference power using the calculated capacitor energy, and calculate a feedback power from realtime current signals received from the current sensor system. The control system compares the feedback power to the reference power, defines a frequency offset based on the comparison, generates a speed command using the frequency offset, and outputs the speed command to the inverter to maintain a smooth DC link voltage during deceleration.

Abstract: A ventilation system includes first and second blowers connected to a plenum in parallel, with a first motor drive to control a speed of an electric motor of the first blower and a second motor drive to control a speed of an electric motor of the second blower. A controller associated with the first blower is programmed to receive a set point for a controlled variable that is controllable by operation of the first and second blowers, estimate a total air flow required from the first and second blowers to reach the controlled variable set point, calculate a blower speed ratio between a first blower speed and a second blower speed that provides the required total air flow at a minimum power consumption level, and generate commands to cause the first blower and the second blower to operate at speeds resulting in the calculated blower speed ratio.

Abstract: A system and method for capturing current information for a power converter is disclosed. The current monitoring system includes a control system operably connected to a circuit having a plurality of semiconductor switches that are controllable to convert an input power to an output power having a desired voltage and current. The control system includes a PWM signal generator to generate switching signals that control switching of the switches, gate drivers to facilitate switching of the switches, and desaturation circuits to provide overcurrent protection to the switches. The control system further includes a processor that receives voltage data from the desaturation circuits regarding a measured voltage across each of the switches, determines a current through each of the switches based on the voltage across each respective switch, and calculates an input current to the circuit or an output current of the circuit based on the determined currents through the switches.

Abstract: A system and method for detecting input phase loss in an adjustable speed drive (ASD) includes an input unit to detect operating data from the ASD. The operating data includes a DC link current of the ASD. The system also includes a state observer that is adapted to receive the operating data from the input unit and extract a DC link capacitor current of the ASD using the DC link current. The system also includes a controller programmed to compare the extracted DC link capacitor current to a predetermined fault range and generate a fault indication of an input phase loss if the extracted DC link capacitor current is within the predefined fault range. The controller is also programmed to calculate an estimated lifespan of the DC link capacitor based on the extracted DC link capacitor current.

Abstract: A system for identifying magnetizing inductance and rotor resistance of an induction machine comprises an induction machine comprising a rotor and a stator, a DC voltage bus, and a DC-to-AC voltage inverter coupled to the DC voltage bus and to the induction machine. The system also comprises a controller configured to cause the DC-to-AC voltage inverter to apply a square-wave excitation to a plurality of phases of the induction machine, determine a stator resistance of the stator of the induction machine based on the square-wave excitation, and determine a rotor resistance of the rotor of the induction machine based on the square-wave excitation. The controller is also configured to calculate a magnetizing curve for the induction machine based on the stator and rotor resistances and control the induction machine to operate based on the magnetizing curve.

Abstract: A system for optimizing switching dead-time includes a power converter that includes a half-bridge circuit comprising a first switch coupled in series with a second switch, first and second state detection circuits respectively coupled to the first and second switches and configured to respectively detect an activation state of the first and second switches. First and second switch control circuits coupled respectively to the first and second switches are configured to respectively toggle the first and second switches between an activate state and a deactivated state. The first switch control circuit includes a first input configured to receive an activation signal from the second state detection circuit indicative of the activation state of the second switch, and the second switch control circuit includes a first input configured to receive an activation signal from the first state detection circuit indicative of the activation state of the first switch.

Abstract: A system and method for detecting high resistance ground faults in a power distribution system is disclosed. A fault detection and protection system is provided that includes a plurality of current sensors to measure current on the three phase output of the converter-inverter arrangement of the power distribution system and a controller configured to measure the three phase current on the three phase output, extract a fundamental current component for each phase of the three phase output, extract a third harmonic component for each phase of the three phase output, compare the fundamental current component and the third harmonic component extracted from each phase to a first threshold and a second threshold, respectively, and detect a ground fault on a phase of the three phase output based on the comparisons of the fundamental current component and the third harmonic component to the first and second thresholds.

Abstract: A system and method for detecting ground faults in an AC motor drive is disclosed. A fault detection and protection system for an AC motor drive includes current sensors to measure first and second phase output currents, a voltage sensor to measure a DC link voltage, and a desaturation control circuit to determine a voltage and associated current across PWM inverter switches for a third phase of the output. A controller compares the first and second phase currents, the measured DC link voltage, and the voltage across the PWM inverter switches on the third phase, to a plurality of thresholds. The controller detects a ground fault on one of the first, second, and third phases of the three phase output to the AC motor based on the comparisons of the first and the second phase currents, the DC link voltage, and the voltage across the switches to the thresholds.

Abstract: A Thyristor Switched Capacitor (TSC) system connected to three sets of diodes and thyristors connected in parallel with the diodes being in an anti-parallel configuration, three capacitors connected in series with the diodes and thyristors, and three surge current controlling reactors that control the transient time to improve power quality in the grid.