Donald W. Novotny

Current Control of VSI-PWM Inverters

The inherent limitations of commanding voltages and currents in a three-phase load with an inverter are examined. An overview of several current controllers described in the literature is presented, and computer simulations are used to compare performance. A switching diagram is developed which reveals some of the operating characteristics of hysteresis controllers. For ramp comparison controllers, a frequency transfer function analysis is used to predict the line currents and provide some insight into the compensation required to reduce the current errors.

A stator flux oriented induction machine drive

The sensitivity of the parameters of a rotor-flux-oriented system using rotor flux estimation is discussed, and a stator-flux-oriented scheme is developed. Since the estimation of the stator flux is independent of the leakage, the steady-state performance of the stator-flux-oriented system is insensitive to the leakage inductance. A decoupler is designed to minimize the coupling in the stator-flux reference frame, improving the dynamic performance of the system. Digital simulation is carried out to show that the performance of the stator-flux-oriented system is superior to that of a detuned rotor-flux-oriented system.<<ETX>>

Design considerations for charge equalization of an electric vehicle battery system

Charge equalization for series-connected battery strings has important ramifications on battery life. It enhances the uniformity of the battery cells and, hence, improves the life of the battery as a whole. A new charge equalization technique for a series string of battery cells has been recently proposed by the authors. The basic technique utilizes a simple isolated DC-to-DC power converter with a capacitive output filter along with a multiwinding transformer. The possibility of integrating the trickle charge function with the charge equalization function is potentially very attractive, as it can lead to an efficient and low-cost implementation.

Motion control with induction motors

Induction motors (IM) provide a very wide speed range, mechanically robust and relatively low cost motion control option. An up-to-date summary of the status of induction motor motion control technology is the subject of this paper. The topics which this paper includes are as follows: basic motion control system requirements; field orientation instantaneous torque control principles for induction motors (FO-IM); current regulators for induction motor motion control; flux and torque regulators for induction motor motion control; self commissioning and continuous self-tuning for field orientation. Technology advances based on modern control and estimation theory have the potential to further enhance the capability of this important class of servo drive systems. >

On-Line Efficiency Optimization of a Variable Frequency Induction Motor Drive

The problems associated with the implementation of an optimal efficiency controller in variable frequency induction motor drives are examined. A simple method for minimizing, on-line, the global system losses is presented. This method is based on the adaptive control of the rotor flux in a field-oriented drive system. The effectiveness of this control strategy is verified using digital simulation.

The Influence of Motor Parameter Deviations in Feedforward Field Orientation Drive Systems

If the value of the time constant used in the slip calculator of a feedforward field orientation drive system deviates from the correct value, the decoupling of flux and torque is lost, and both steady-state and transient response is degraded. An analysis of detuned operation shows that the amount of performance degradation is strongly dependent on machine parameters. The large magnetizing inductance and low rotor resistance typically associated with larger, more efficient machines is shown to tend to amplify the effects of detuning compared to the relative insensitivity of small low-efficiency machines. It is also shown that for many applications the transient response effects of detuning can be handled by the outer control loops and that the major problem is maintaining the steady-state operating flux and current at reasonable levels.

Field Weakening in Buried Permanent Magnet AC Motor Drives

The usual uncoupled d - q model of salient pole synchronous machines (Parks model) may be insufficient for accurate modeling of buried magnet permanent magnet machines. The addition of a nonbilateral coupling between the direct and quadrature axis equivalent circuits is shown to improve the steady-state model greatly. The cross coupling reactance has important implications in improving operation in the constant horsepower mode. In particular, it is demonstrated that the cross coupling term acts to reduce the effective internal voltage so that some field weakening can be achieved. The results should be useful in permanent magnet machine design for variable speed drive applications.

Implementation of direct stator flux orientation control on a versatile DSP based system

A direct stator flux orientation control for induction machines was implemented on a versatile Motorola 56000 digital signal processor (DSP)-based system. Some practical aspects of implementing direct stator flux orientation (DSFO) control, such as parameter identification, flux estimation, and rotor angular velocity estimation, are discussed. Experimental results are presented to show the performance of a DSFO-controlled induction machine drive. Comparison between DSFO and direct rotor flux orientation (DRFO) control shows that DSFO is superior to DRFO in the field-weakening region.<<ETX>>

The universal field oriented controller

The synthesis of a universal field-oriented (UFO) controller is presented. The UFO is capable of decoupling flux and torque in an arbitrary reference frame. Due to its high degree of generality, it is fully compatible with all existing field-oriented controllers, indirect as well as direct. As a consequence, the digital integration of the UFO scheme in all induction motor drives with the same hardware and software is feasible. Examples are worked out using a high-speed digital signal processor. It is noted that in certain operating conditions the flexibility of changing the flux reference frame can extend the stability region or the torque capability curves of the drive. Detuning problems in field orientation are handled in an optimal manner for each field-oriented controller by proper selection of the model of the induction machine and its reference frame.<<ETX>>

Analysis of surface permanent magnet machines with fractional-slot concentrated windings

This paper presents a closed-form analytical technique for analyzing surface PM machines equipped with fractional-slot concentrated windings. Since this class of winding configuration deviates significantly from conventional sinusoidal distributions, classical steady-state phasor or dq analytical techniques cannot be used to provide accurate results. The presented analytical model provides a fast and reliable method to analyze and compare candidate machine designs. Stator slotting effects are taken into consideration and a wide range of concentrated winding configurations can be analyzed. This technique is capable of analyzing the machine both below (constant-torque) and above (flux-weakening) base speed. Average torque, cogging torque, and ripple torque are all evaluated. Analytical results are verified using finite element analysis.