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Advancements in ac industrial drives have been propelled through improvements in power electronics and control hardware. Improvements in insulated gate bipolar transistors (IGBTs) allowed faster switching speeds, which provides lower thermal losses. Digital signal processors and improved control algorithms allow ac drives to address applications previously handled by dc drives. Capacitive coupling between the IGBT, power structure, and control platform components influence drive dynamics and contributes to signal and waveform distortion. This differential and common mode capacitance is often disregarded as 'parasitics' and not considered in designing the control. This paper decouples the major contributors to motor waveform distortion, analyzes them, quantifies them, and presents a correction strategy. Simulations validate the analysis and experimental results demonstrate the strategy's benefits. Index Terms--Capacitive coupling long cables, dead time compensation, IGBT, parasitics, power device drop, power device dynamics, voltage distribution.

In this paper, a generalized discontinuous pulsewidth modulation (GDPWM) method with superior high modulation operating range performance characteristics is developed. An algorithm which employs the conventional space-vector PWM method in the low modulation range, and the GDPWM method in the high modulation range, is established. As a result, the current waveform quality, switching losses, voltage linearity range, and the overmodulation region performance of a PWM voltage-source inverter (PWM-VSI) drive are on-line optimized, as opposed to conventional modulators with fixed characteristics. Due to its compactness, simplicity, and superior performance, the algorithm is suitable for most high-performance PWM-VSI drive applications. This paper provides detailed performance analysis of the method and compares it to the other methods. The experimental results verify the superiority of this algorithm to the conventional PWM methods. Index Terms - Discontinuous modulation, harmonics, inverter, pulsewidth modulation, switching losses.

In this paper, the overmodulation region voltage-gain characteristics and waveform quality of carrier-based pulsewidth-modulated (PWM) methods are investigated. Through detailed analytical study, voltage-gain characteristics are extracted independent of carrier frequency. The influence of blanking time and minimum pulsewidth (MPW) control on the inverter gain characteristics are studied and shown to be significant. A comparative evaluation of the modulator characteristics reveals the advantageous high-modulation-range characteristics of discontinuous PWM methods and, in particular, the superior overmodulation performance of a discontinuous PWM method. The modulation methods under consideration are tested on a PWM voltage-source inverter (VSI)fed induction motor drive in the laboratory, and the theoretical results are verified by experiments. Also, a gain linearization technique is presented and experimentally verified. The results of this study are useful in design, performance prediction, and development of high-performance overmodulation strategies for PWM-VSI drives. Index Terms - Current harmonics, inverter, overmodulation, voltage gain.

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. Index Terms - DC-link, field-oriented control (FOC), field-weakening, overmodulation, rotor-flux-oriented (RFO), stator-flux-oriented (SFO), torque capability, voltage margin.

This paper evaluates a new induction motor, the electrostatic shielded induction motor (ESIM). An ESIM reduces rotor shaft voltages to levels below the bearing lubricant's electric field intensity breakdown level and offers one solution to accelerated bearing wear caused by fluting induced by pulsewidth modulated (PWM) inverters. The paper begins by reviewing shaft voltages and the resulting bearing currents when operated on PWM voltage source inverters. An example of bearing fluting is shown, and system models are presented and discussed. The construction details and test results for several ESIM's are presented. Experimental results show the ESIM solves the electrostatically induced rotor shaft voltage and bearing problem without degrading the electromagnetic performance of the motor. Index Terms - Bearing capacitance, bearing current, bearing current density, bearing voltage ratio, electric discharge machining, electrostatic shielded induction motor, rotor-shaft-to-ground voltage, stator-to-rotor capacitance.

This paper investigates overvoltage transients on ac induction motors when connected through a cable of arbitrary length to a variable frequency drive (VFD) consisting of a pulsewidth modulation (PWM) inverter with insulated gate bipolar transistor (IGBT) power devices. Factors contributing to a motor overvoltage transient equal to a theoretical twice dc bus voltage are first described using existing transmission line analysis. A critical cable distance [l.sub.c] is defined where this 2-pu overvoltage occurs. However, literature is lacking on how motor voltage transients >2-pu bus voltage and up to 3-4 pu are generated. This phenomenon is observed on all PWM inverters with output cable lengths greater than [l.sub.c] distance. Contributing factors to the >2-pu overvoltage phenomenon are investigated by exploring the complex interaction between drive modulation techniques, carrier frequency selected, cable natural frequency of oscillation, cable high-frequency damping losses, and, to a lesser extent, inverter output rise time. Theoretical calculations of cable frequency and damping are correlated with simulation and experimental results. Novel modifications to the PWM modulator, as well as external hardware apparatus, are proposed solutions to the >2-pu overvoltage problem; both are simulated and experimentally confirmed. Index Terms - Cable impedance, pulse elimination technique (PET), transient overvoltages, voltage reflection.

The dead time necessary to prevent the short circuit of the power supply in pulsewidth-modulated (PWM) voltage inverters results in output voltage errors. Although individually small, when accumulated over an operating cycle, the voltage errors are sufficient to distort the applied PWM signal. This paper presents a method to correct for the dead-time errors. The pulse-based dead-time compensator (PBDTC) is less hardware- and software-intensive than other dead-time compensation methods providing a low-cost solution. The pulse-based technique is developed by analyzing the effects of dead time on a pulse-by-pulse basis and correcting each pulse accordingly. The technique is evaluated through simulation and experimental results. Other compensation methods are evaluated, and the results compared with the pulse-based technique. This comparison indicates previous methods can produce magnitude and phase errors in the applied terminal voltage, whereas the proposed method compensates for the dead time without significant magnitude and phase errors in the terminal voltage of PWM voltage source inverters. Index Terms - Dead time (DT), instabilities, power semiconductor devices, pulse-based dead-time compensator (PBDTC), turn-on delay (TD), unsymmetrical pulses.

This paper examines ac motor shaft voltages and the resulting bearing currents when operated under pulse width modulation (PWM) voltage source inverters. The paper reviews the mechanical and electrical characteristics of the bearings and motor in relation to shaft voltages and bearing currents. A brief review of previous work is addressed, including the system model and experimental results. The theory of electric discharge machining (EDM) is presented, including component calculations of the system elements. The effect of system elements on shaft voltages and bearing currents are evaluated experimentally and the results compared to theory. A design calculation is proposed that provides the relative potential for EDM. Finally, the paper will present quantitative results on one solution to the shaft voltage and bearing current problem. Index Terms - Bearing capacitance, bearing current, bearing current density, bearing threshold voltage, electric discharge machining, electrostatic shielded induction motor, rotor shaft to ground voltage, stator to rotor capacitance.

This paper examines ac motor shaft voltages and resulting bearing currents when operated under pulse width modulation (PWM) voltage source inverters. The paper reviews the electrical characteristics of bearings and motors that cause shaft voltages and bearing currents. A brief review of previous work is presented, including a system model for electrical analysis of bearing currents. Relying on the work of a companion paper, the propensity for electric discharge machining (EDM) is determined by a design equation that is a function of system components. Pertinent machine parameters and their formulas are presented and values calculated for machines from 5 to 1000 hp. The effects of system elements on shaft voltages and bearing currents are evaluated experimentally and the results compared to theory. Finally, the paper will present quantitative results for one solution to the shaft voltage and bearing current problem. Index Terms - Bearing capacitance ([C.sub.b]), bearing current ([I.sub.b]), bearing threshold voltage ([V.sub.th]), bearing voltage ratio (BVR), electric discharge machining (EDM), electrostatic shielded induction motor (ESIM), rotor shaft to ground voltage ([V.sub.rg]), stator to rotor capacitance ([C.sub.sr]).

Modern power inverters provide the industrial control industry with significant advantages. The faster switching devices have increased drive performance, but with some recently discovered disadvantages. One disadvantage, rotor shaft voltage and resulting bearing current, has become an industry concern. The oil film in a bearing acts as a capacitor and provides a charging mechanism for rotor shaft voltage buildup. Electrical breakdown of the film can damage the bearing. This paper examines the mechanical and electrical characteristics of the bearing and converts them into models. The mechanical model for the bearing contact area establishes an allowable bearing current density, which is used to estimate the electrical life of a mechanical bearing. The electrical model for the bearing provides a significant advancement, aids bearing design, and the analysis of electrically induced bearing damage. Finally, the paper presents quantitative results for one solution to the shaft voltage and bearing current problem. Index Terms - Bearing capacitance, bearing current, bearing current density, bearing threshold voltage, electric discharge machining, electrostatic shielded induction motor, rotor shaft-to-ground voltage, stator-to-rotor capacitance.

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.

The paper presents a deterministic method of estimating the transient inductance and rotor resistance of an induction machine for field commissioning purposes. The parameter values obtained by the method are compared with those for a transient method of commissioning. Skin effects inherent with the transient test are documented. Experimental results for a wide range of machine sizes are included for both methods. The quality of field orientation is established for each method through experimental testing.

This paper investigates ac induction motor shaft voltage problems, current flow thru motor bearings and electric discharge current problems within bearings when operated under both pure sinewave and pulse width modulated (PWM) inverter sources. Recent experience suggests that PWM voltage sources with steep wavefronts especially increase the magnitude of the above electrical problems, leading to motor bearing material erosion and early mechanical failure. Previous literature suggests that shaft voltage - bearing current problems under 60 Hz sinewave operation are predominantly electromagnetically induced. It is proposed that under PWM operation these same problems are now predominantly an electrostatic phenomenon. A system model to describe this phenomenon is characterized and developed. Construction and test of a new electrostatic shielded induction motor (ESIM) verifies this model and is also a possible solution to the bearing current problem under PWM operation.

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 CMT's smooth transition to six-step and the improved performance a CMT-PWM algorithm provides.

A self-organized field-oriented induction machine controller that addresses problems encountered in the field-weakening region is presented. The field-oriented controller (FOC) is based on model reference adaptive principles but relies on samples of the state of the machine to determine control inputs. The proposed controller is compared with other approaches to field-weakening operation, and the advantages and limitations of each are discussed. Experimental results are presented for the classical and the self-organized approaches to field-weakening operation.

Reflected-wave transient voltages that result from fast insulated gate bipolar transistor (IGBT) voltage-source inverters have received considerable investigation. The modeling and simulation of these transients require sophisticated motor and cable models. Most voltage-source pulsewidth modulated (PWM) adjustable-speed drive suppliers now provide combinations of passive and active control techniques to mitigate the adverse effects of overvoltage stress, however, the costs of the passive fixes often exceed the cost of the drive. Another aspect of low-rise-time devices, heretofore not examined to the extent of the overvoltage problem, is the resulting current from traveling waves. In this paper, a historical perspective of the overvoltage problem is presented. Models of system components are reviewed, and simulation results are compared with experimental results. These models are then employed to predict the peak currents from voltage-source inverters as the cable, load, and IGBT rise time are altered. The paper will then examine the consequences of reflected wave currents on current sensing, drive control, and device performance. From these results, a minimum rise time is established. Index Terms--Common-mode noise, current sensor, high-frequency current, insulated gate bipolar transistor rise time, motor overvoltage, reflected wave.

Reflected-wave transient voltages that result from fast insulated gate bipolar transistor voltage-source inverters have received considerable investigation. Modeling, simulation, and attenuation of these transients require sophisticated motor and cable models. Most drive suppliers now provide combinations of passive and active solutions to mitigate the adverse effects of overvoltage stress, however, the costs of the passive solutions often exceed the cost of the drive. Another aspect of low-rise-time devices, not examined to the extent of the overvoltage problem, is the resulting current from traveling waves. Current sensor fidelity limits the ability of modern drives to detect peak current and can result in current feedback distortion. This paper presents recent research into the response, modeling, and construction of Hall-effect current sensors. Models for Hall-effect current sensors are introduced and compared. Experimental and simulation results demonstrate the complexity of the common current sensors employed in modern adjustable-speed drives. A comparison of the sensor response and the model's prediction demonstrates the difficulty associated with accurate current detection. Finally, the paper presents design guidelines to reduce the corrupting influence of high-frequency differential and common-mode currents. Index Terms--Current sensor, feedback device, Hall effect, reflected waves.

Adjustable-speed drives with regenerative pulsewidth modulation rectifiers—both voltage source rectifiers and current source rectifiers—have $LC$ filters on their input to attenuate the high-frequency components of current and achieve reduced levels of total harmonic distortion. The capacitors used in these filters are predominantly of the metalized film construction and are prone to catastrophic failure. In this paper, a method is proposed for the detection of capacitor degradation and location of the faulted phase. The method uses measurements of voltages and currents—which may already be available for control purposes, for line synchronization and active damping—to detect impedance asymmetry and is impervious to input voltage unbalance. [ABSTRACT FROM PUBLISHER]

In this paper, dynamic overmodulation characteristics of current-regulated carrier-based high-performance pulsewidth modulation (PWM) voltage-source inverter drives are investigated. Dynamic and steady-state overmodulation operating modes are clearly distinguished, and the requirements for obtaining high performance in each mode are shown to be significantly different. Dynamic overmodulation characteristics of the modern triangle intersection PWM methods are modeled and shown to be unique for each method. The study reveals space-vector PWM (SVPWM) exhibits a minimum voltage magnitude error characteristic. It also indicates all the advanced triangle intersection PWM methods, including SVPWM, have limited dynamic overmodulation performance. To enhance the performance, an algorithm with superior performance is adapted from the direct digital PWM approach. Detailed induction motor drive simulations and experimental results illustrate the characteristics of modern triangle intersection PWM methods and the performance gained with the new dynamic overmodulation algorithm. Index Terms - Dynamics, inverter, modulation, overmodulation, pulsewidth modulation.

This paper provides analytical and graphical methods for the study, performance evaluation, and design of the modern carrier-based pulsewidth modulators (PWM's), which are widely employed in PWM voltage-source inverter (VSI) drives. Simple techniques for generating the modulation waves of the high-performance PWM methods are described. The two most important modulator characteristics - the current ripple and the switching losses - are analytically modeled. The graphical illustration of these often complex multivariable functions accelerate the learning process and help one understand the microscopic (per-carrier cycle) and macroscopic (per fundamental cycle) behavior of all the modern PWM methods. The analytical formulas and graphics are valuable educational tools. They also aid the design and implementation of the high-performance PWM methods. Index Terms - Analysis, graphics, harmonics, inverter, modulation, PWM, switching losses, voltage linearity, VSI.