Brian J. Seibel

A new flux and stator resistance identifier for AC drive systems

The effect of stator resistance on AC drive performance is analyzed for flux vector and indirect field-oriented controllers. A new technique-the back electromagnetic force (BEMF) detector-for reducing the adverse effects of stator resistance on field-oriented control is presented and evaluated through simulation and experimental results. The BEMF detector is shown to reduce the impact of the stator resistance variations and also provide an estimate of the stator resistance. The detector is compatible with most control strategies and with or without position feedback.

Field-oriented control of an induction machine in the field-weakening region with DC-link and load disturbance rejection

A method of actively maintaining voltage margin in field-oriented induction machine controllers is proposed. A voltage-margin controller is developed that rejects DC-link and load disturbances, such that current regulation and field orientation is maintained. In addition, the voltage-margin controller coupled with rotor-flux-oriented control is shown to provide maximum torque capability equivalent to stator-flux-oriented control.

Operation of PWM voltage source-inverters in the overmodulation region

Pulse width modulated (PWM) inverters experience a reduction in gain when overmodulation occurs. The pulse dropping or transition region is examined for continuous and discontinuous modulation strategies. Transition region characteristics for a number of modulation strategies are introduced. The effect of the transition region on field oriented control (FOC) is presented. The adverse effects of bus disturbances on current regulated AC inverters, while in the transition region, are demonstrated by experimental results. The problems encountered are the consequence of the reduced gain of the PWM inverter regardless of the PWM strategy. A compensated modulation technique (CMT) adaptable to continuous and discontinuous modulators eliminates the voltage error and transitions to six-step operation without inducing a voltage transient. The CMT applies to voltage and current regulated PWM inverters employing most of the modern switching strategies. Experimental results presented in the paper demonstrate the CMTs smooth transition to six-step and the improved performance a CMT-PWM algorithm provides.

A simplified inverter model for on-line control and simulation

A simplified fundamental component model for sine triangle comparison pulse width modulated (PWM) inverters operating in the transition region is presented. The model is evaluated by comparing it to detailed inverter simulations and through experimental verification. Results from a real-time control application show that the model compensates for the reduced inverter gain due to bus voltage variation and operation in the pulse dropping region. Application of the model to high-performance drives is explored.<<ETX>>

Control of PWM voltage inverters in the pulse dropping region

The overmodulation of pulse width modulated (PWM) inverters causes a nonlinearity in the feedforward channel. The type of modulator, sine wave, space vector, or third harmonic, establishes the characteristics of the transition regions nonlinearity. The characteristics for a number of modulation strategies are introduced. Test results from commercially available volts per hertz (V/F) drives reveal their inability to provide rated voltage even at rated input conditions. The adverse effects of the overmodulation region on current regulated AC inverters are demonstrated by experimental results. A compensated modulation technique (CMT), adaptable to continuous and discontinuous modulators, provides the exact inverse of the nonlinearity; thus it produces a smooth transition to six-step operation without inducing a voltage transient. Experimental results presented in the paper demonstrate the CMTs smooth transition to six-step and the improved performance of the CMT-PWM. Finally, a comparison of the CMT with the other known overmodulation strategy shows the CMT provides a simple technique with essentially identical harmonic characteristics.<<ETX>>

Inverter control during overload and following power interruption

A frequency control method is presented that interacts with a voltage-controlled current-regulated pulse-width modulation (CRPWM) inverter to provide operation during and after a momentary overload and reconnection to a de-energized rotating motor under load. This is accomplished without overcurrent trips, knowledge of motor parameters, or velocity feedback. In addition, a stability study of the synchronous voltage-controlled CRPWM inverter is performed that determines the effects of controller, motor, and load variations on the region of instability. Results reveal that the synchronous voltage-controlled CRPWM inverter and traditional open velocity loop PWM inverter have similar unstable regions with respect to operating frequency.<<ETX>>

Industrial regenerative motor-drive systems

Regenerative motor-drive systems are nowadays widely applied in numerous industrial applications. This paper is centered on comparing the application of the two well-known and widely used types of regenerative front end converters. Namely, Fundamental Front End (FFE) rectifier, and Active Front End (AFE). The paper also introduces a new control topology for the temporary operation of the FFE converter. This topology enables to temporary boost the DC bus voltage and consequently provides an enhanced ride through operation for the FFE. As well be shown, this control topology can be considered as a “quasi-AFE” as it utilizes four switching states of conventional AFE without employing current controllers and with reduced switching losses. Theory, analysis, simulation, and experimental results are presented to prove and support the technical discussion subject of this paper.

Operation of induction machines with electromagnetic irregularities

The paper presents application data showing an induction motor developing torque at zero slip. This condition can prevent proper field commissioning of the motor drive system and contribute to inferior system performance. The paper examines rotor asymmetries, one cause for the nonzero torque condition. Voltage and current spectra, for current regulated and volts per hertz controllers, are presented. Another source for the nonzero torque at zero slip, machine space harmonics, is discussed and analyzed. The paper examines contributions to abnormal machine operation of each source by examining the signals present in the respective waveforms. Control strategies are developed where appropriate to mitigate the adverse effects of the motor irregularities.

Field oriented control of an induction machine with DC link and load disturbance rejection

A method of actively maintaining voltage margin in field oriented induction machine controllers is proposed. A voltage margin controller is developed that rejects DC link and load disturbances such that current regulation and field orientation is maintained. In addition, the voltage margin controller coupled with rotor flux oriented control is shown to provide maximum torque capability equivalent to stator flux oriented control.

A new instantaneous point on wave voltage sag detection algorithm & validation

In industrial applications, power quality has been an issue drawing increasing concerns due to its severe consequences on system performance and downtime cost. Voltage sags are classified as one of the most common power quality issues. In order to guarantee system operation under several line sag scenarios, international standards such as SEMI F47, IEC-61000-4-34, and IEC-61000-4-11 have been established as guidelines for electrical/electronics manufacturers. In this paper, an innovative point on wave sag detection is introduced. Although the main focus of this work is centered on applications related to regenerative motor-drive systems, this approach can be utilized in a myriad of other applications such as grid-tie inverters, uninterrupted power supplies and advanced relay protection. In addition, the introduced technique is very effective at detecting repeated line sag conditions. The introduced detection method has been experimentally validated using a 20 HP regenerative motor-drive system setup under various line sag scenarios.