Douglas K. Lindner

Input filter interaction in three phase AC-DC converters

It is well known that the addition of an input filter preceding a switched mode regulator poses a problem of performance degradation and potential instability due to its negative input impedance at low frequencies. Three phase converters are essentially multivariable systems. The objective of this paper is to analyze the problem of input filter interaction in three phase AC-DC converters from a multivariable perspective and to establish criteria that guarantee stability and satisfactory performance of the converter with an input filter. The dq average model of a three phase boost rectifier is used for the analysis. The minor loop, the stability of which has to be guaranteed is identified. A sufficient condition for stability, based on the singular values of the filter output impedance and converter input admittance matrices is derived. Simulation results are presented to illustrate the results.

Design of a boost power factor correction converter using optimization techniques

This paper presents an approach to continuous variable design optimization of a power electronics converter. The objective of the optimization approach is to minimize the total component cost. The methodology is illustrated with the design of a boost power factor correction front-end converter with an input electromagnetic interference filter. The system design variables are first identified. The relevant system responses and component costs are then expressed as a function of these design variables. Finally, by using mathematical optimization techniques, the design variable values that minimize the total system component cost are obtained, given practical constraints on these design variables and system responses.

Average modeling of three-phase and nine-phase diode rectifiers with improved AC current and DC voltage dynamics

This paper presents a new average modeling approach for three-phase and nine-phase diode rectifiers with improved AC and DC dynamics. The key assumption taken in this paper is to model the DC load current using its first-order Taylor series expansion throughout the entire averaging timespan, i.e., commutation and conduction periods. The resultant average models present an excellent steady-state and transient behavior, matching their respective detailed switching models with less than 1 % measured error. Moreover, the analytic nature of these models makes them suitable for simulation and stability studies of variable frequency power systems. The paper presents an in-depth description of the modeling approach, together with a thorough static and transient validation of the proposed models. The model is validated through comparison of average model in MATLAB, switching model in Saber and the experimental results

Vibration suppression using a proofmass actuator operating in stroke/force saturation

The design of the control-loop structure for a feedback control system which contains a proofmass actuator for suppressing vibration is discussed. The loop structure is composed of inner control loops, which determine the frequency of the actuator and which are directly related to the actuator and the outer loops which add damping to the structure. When the frequency response of the actuator is matched to the stroke/force saturation curve, the actuator is most effective in the vibration suppression loops, and, since the stroke/force saturation curve is characterized by the stroke length, the mass of the proofmass, and the maximum current delivered by the motor electronics, the size of the actuator can be easily determined. The results of the loop-structure model calculations are verified by examining linear DC motors as proofmass actuators for the Mast in NASAs Control of Flexible Structures program.

Optimized design of switching amplifiers for piezoelectric actuators

The formulation and solution of an optimization problem for the design of a current controlled switching power amplifier to drive a piezoelectric actuator is the subject of this paper. The design is formulated as a continuous optimization problem. A detailed model that includes the anhysteretic nonlinearity between the electric field and polarization is developed and is coupled with a dynamic model of the amplifier. The design specifications are formulated as optimization constraints. The objective function is chosen to be the weight of the inductor. Optimization results are presented to demonstrate the efficiency of the proposed design methodology.

Design of a piezoelectric actuator and compliant mechanism combination for maximum energy efficiency

The combined optimization of a compliant mechanism and a piezoelectric stack actuator for maximum energy conversion efficiency is considered. The analysis assumes all components to be free from dissipation and that the piezoelectric stack actuator is driven by an ideal sinusoidal voltage source. The energy conversion efficiency is defined as the ratio of the output mechanical energy to the input electric energy. Using linear two-port models, an analytical expression for the maximum energy conversion efficiency is derived. It is shown that the optimization of the piezoelectric stack actuator can be decoupled from the topology optimization of the compliant mechanism. Computational verification of the analytical results is presented for two ground structures modeled using frame elements. The trade-off between displacement amplification and maximization of the energy conversion efficiency is examined.

Power Flow through Controlled Piezoelectric Actuators

In this paper we investigate the power requirements of a piezoelectric actuator operating in a damping augmentation loop. When the piezoelectric actuator is driven by a current amplifier, we show that acceleration feedback augments the damping of the structure without changing the stiffness. Using this controller, we determine the real and reactive power flow through the structure and actuator into the amplifier when the structure is excited with a sinusoidal disturbance force. Estimates of the real and reactive power flow in terms of the actuator parameters are given. These estimates are useful for sizing the drive amplifier for the actuator.

Zeros of modal models of flexible structures

It is shown that in some situations the zero patterns of a flexible structure change radically with model order. The refinement of the model by the addition of higher-order modes can cause zeros to appear at low frequencies or in the right half-plane. Structures instrumented with piezoelectric actuators and/or fiber-optic sensors are also considered. >

Power systems and requirements for integration of smart structures into aircraft

Electrical power distribution for recently developed smart actuators becomes an important air-vehicle challenge if projected smart actuation benefits are to be met. Among the items under development are variable shape inlets and control surfaces that utilize shape memory alloys (SMAs); full-span, chord-wise and span-wise contouring trailing control surfaces that use SMA or piezoelectric materials for actuation; and other strain-based actuators for buffet load alleviation, flutter suppression and flow control. At first glance, such technologies afford overall vehicle performance improvement. However, integration system impacts have yet to be determined or quantified. Power systems to support smart structures initiatives are the focus of the current paper. The paper has been organized into five main topics for further discussion: (1) air-vehicle power system architectures – standard and advanced distribution concepts for actuators, (2) smart wing actuator power requirements and results highlighting wind tunnel power measurements from SMA and piezoelectric ultrasonic motor-actuated control surfaces and different dynamic pressure and angle of attack; (3) vehicle electromagnetic effects (EME) issues, (4) power supply design considerations for smart actuators featuring the aircraft power and actuator interface, and (5) summary and conclusions.

Analysis of subsystem integration in aircraft power distribution systems

Stability analysis of a baseline power system architecture for modern aircraft is addressed. Power electronic converters are widely used in modern aircraft power distribution systems. Due to their inherent nonlinear characteristics, instabilities may arise while integrating individual subsystems together. Bifurcation analysis is used to identify the type, multiplicity and stability of system trajectories. The complete bifurcation diagram for the baseline power system is drawn. The dependence of the parameter values on the bifurcation behavior of the baseline system is presented.