Robert D. Lorenz

Bio: Robert D. Lorenz is an academic researcher from University of Wisconsin-Madison. The author has contributed to research in topics: Torque & Direct torque control. The author has an hindex of 68, co-authored 474 publications receiving 17355 citations.

A physically insightful approach to the design and accuracy assessment of flux observers for field oriented induction machine drives

Abstract: Rotor flux observers can provide an attractive means for achieving direct field oriented control of induction machines. This paper presents a physics-based design methodology and uses it to evaluate open-loop observers and to develop a new closed-loop flux observer. It is shown that the new flux observer is a straightforward structure with properties that combine the best features of known methods. A distinction is made between observers, which use only integration and feedback summation operations, and those estimation methods requiring approximate differentiation which are, in essence, "cancellation" methods. Furthermore, a clear distinction is made between accuracy and dynamic robustness of the observer. This distinction is important because the accuracy of flux observers for induction machines is inherently parameter sensitive, whereas robustness of observers, in a controls sense, is not parameter sensitive. Moreover, it is shown how flux observers can provide robust field oriented control because the flux angle is substantially more correct than the flux magnitude. A distinctive form of frequency response function (FRF) analysis similar to that used in classical control engineering is demonstrated to be a useful and insightful tool even though flux observers are multiple-input, multiple-output systems. Finally, the limits of such flux observers are experimentally evaluated. >

Using multiple saliencies for the estimation of flux, position, and velocity in AC machines

Abstract: This paper presents an improved method of estimating the flux angle, rotor position and velocity by tracking the position of spatial saliencies in an AC machine. Specifically, a machine model is presented which accurately models the behavior of AC machines with multiple spatial harmonic saliencies. The effects of multiple spatial harmonic saliencies on the estimation of flux angle, position and velocity is analyzed, and methods are presented utilizing multiple spatial harmonic saliencies to provide wide bandwidth, high accuracy estimates of machine flux angle, rotor position and velocity.

Control topology options for single-phase UPS inverters

Abstract: Four control topologies for single-phase uninterruptible power system (UPS) inverters are presented and compared, with the common objective of providing a dynamically stiff, low total harmonic distortion (THD), sinusoidal output voltage. Full-state feedback, full-state command controllers are shown, utilizing both filter inductor current and filter capacitor current feedback to augment output voltage control. All controllers presented include output voltage decoupling in a manner analogous to "back EMF" decoupling in DC motor drives. Disturbance input decoupling of the load current and its derivative is presented. An observer-based controller is additionally considered and is shown to be a technically viable, economically attractive option. The accuracy transfer function of the observer estimate is used to evaluate its measurement performance. Comparative disturbance rejection is evaluated by overlaying the dynamic stiffness (inverse of output impedance) frequency response of each controller on a single plot. Experimental results for one controller are presented.

Analysis and design of current regulators using complex vectors

Abstract: The analysis and design of current regulators for multiphase AC loads in AC machines is presented using complex vector notation. The use of complex vector notation provides a way of comparing the performance of controller topologies through their complex vector root locus and complex vector frequency-response functions. Limitations in the performance of the synchronous frame proportional plus integral current regulator are outlined and several ways of improving its performance are suggested and investigated.

Finite-Control-Set Model Predictive Torque Control With a Deadbeat Solution for PMSM Drives

Abstract: This paper proposes a control strategy of finite-control-set model predictive torque control (FCS-MPTC) with a deadbeat (DB) solution for permanent-magnet synchronous motor drives. By using a DB solution, the process of selection of the best switching vector is optimized. The predicted DB voltage sector consisting of the desired voltage vector (VV) avoids the complete enumeration for testing all feasible VVs, which relieves the big calculation effort of the traditional FCS-MPTC method. The proposed system is experimentally carried out both in the steady state and in the transient state.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

From PID to Active Disturbance Rejection Control

Abstract: Active disturbance rejection control (ADRC) can be summarized as follows: it inherits from proportional-integral-derivative (PID) the quality that makes it such a success: the error driven, rather than model-based, control law; it takes from modern control theory its best offering: the state observer; it embraces the power of nonlinear feedback and puts it to full use; it is a useful digital control technology developed out of an experimental platform rooted in computer simulations ADRC is made possible only when control is taken as an experimental science, instead of a mathematical one It is motivated by the ever increasing demands from industry that requires the control technology to move beyond PID, which has dominated the practice for over 80 years Specifically, there are four areas of weakness in PID that we strive to address: 1) the error computation; 2) noise degradation in the derivative control; 3) oversimplification and the loss of performance in the control law in the form of a linear weighted sum; and 4) complications brought by the integral control Correspondingly, we propose four distinct measures: 1) a simple differential equation as a transient trajectory generator; 2) a noise-tolerant tracking differentiator; 3) the nonlinear control laws; and 4) the concept and method of total disturbance estimation and rejection Together, they form a new set of tools and a new way of control design Times and again in experiments and on factory floors, ADRC proves to be a capable replacement of PID with unmistakable advantage in performance and practicality, providing solutions to pressing engineering problems of today With the new outlook and possibilities that ADRC represents, we further believe that control engineering may very well break the hold of classical PID and enter a new era, an era that brings back the spirit of innovations

Review of Battery Charger Topologies, Charging Power Levels, and Infrastructure for Plug-In Electric and Hybrid Vehicles

Abstract: This paper reviews the current status and implementation of battery chargers, charging power levels, and infrastructure for plug-in electric vehicles and hybrids. Charger systems are categorized into off-board and on-board types with unidirectional or bidirectional power flow. Unidirectional charging limits hardware requirements and simplifies interconnection issues. Bidirectional charging supports battery energy injection back to the grid. Typical on-board chargers restrict power because of weight, space, and cost constraints. They can be integrated with the electric drive to avoid these problems. The availability of charging infrastructure reduces on-board energy storage requirements and costs. On-board charger systems can be conductive or inductive. An off-board charger can be designed for high charging rates and is less constrained by size and weight. Level 1 (convenience), Level 2 (primary), and Level 3 (fast) power levels are discussed. Future aspects such as roadbed charging are presented. Various power level chargers and infrastructure configurations are presented, compared, and evaluated based on amount of power, charging time and location, cost, equipment, and other factors.