Showing papers on "Feedback loop published in 1996"

Tracking control of a piezoceramic actuator

Abstract: The tracking control accuracy of piezoceramic actuators is limited due to their inherent hysteresis nonlinearity. This paper presents a computer-based tracking control approach for a piezoceramic actuator based on incorporating a feedforward loop with a PID (proportional-integral-derivative) feedback controller. The hysteresis nonlinearity of the piezoceramic actuator is modeled in the feedforward loop by using the classical Preisach model. Experiments were performed on a stacked piezoceramic actuator for tracking sinusoidal waveforms with signal frequencies ranging from 0.1-20 Hz. A comparison was made between a feedforward control scheme, a regular PID feedback control scheme, and a PID feedback control scheme with hysteresis modeling in the feedforward loop. The results show that the tracking control performance is greatly improved by augmenting the feedback loop with a model of hysteresis in the feedforward loop. The maximum error in tracking a sinusoidal waveform is about half that obtained using a regular PID controller.

Analysis and design of a multiple feedback loop control strategy for single-phase voltage-source UPS inverters

Abstract: This paper presents the analysis and design of a multiple feedback loop control scheme for single-phase voltage-source uninterruptible power supply (UPS) inverters with an L-C filter. The control scheme is based on sensing the current in the capacitor of the load filter and using it in an inner feedback loop. An outer voltage feedback loop is also incorporated to ensure that the load voltage is sinusoidal and well regulated. A general state-space averaged model of the UPS system is first derived and used to establish the steady-steady quiescent point. A linearized small signal dynamic model is then developed from the system general model using perturbation and small-signal approximation. The linearized system model is employed to examine the incremental dynamics of the power circuit and select appropriate feedback variables for stable operation of the closed-loop UPS system. Experimental verification of a laboratory model of the UPS system under the proposed closed-loop operation is provided for both linear and nonlinear loads. It is shown that the control scheme offers improved performance measures over existing schemes, It is simple to implement and capable of producing nearly perfect sinusoidal load voltage waveform at moderate switching frequency and reasonable size of filter parameters. Furthermore, the scheme has excellent dynamic response and high voltage utilization of the DC source.

Conditions for Robustness and Nonrobustness of theStability of Feedback Systems with Respect to Small Delays inthe Feedback Loop

Abstract: It has been observed that for many stable feedback control systems, the introduction of arbitrarily small time delays into the loop causes instability. In this paper we present a systematic frequency domain treatment of this phenomenon for distributed parameter systems. We consider the class of all matrix-valued transfer functions which are bounded on some right half-plane and which have a limit at $+\spinfty$ along the real axis. Such transfer functions are called regular. Under the assumption that a regular transfer function is stabilized by unity output feedback, we give sufficient conditions for the robustness and for the nonrobustness of the stability with respect to small time delays in the loop. These conditions are given in terms of the high-frequency behavior of the open-loop system. Moreover, we discuss robustness of stability with respect to small delays for feedback systems with dynamic compensators. In particular, we show that if a plant with infinitely many poles in the closed right half-plane is stabilized by a controller, then the stability is not robust with respect to delays. We show that the instability created by small delays is itself robust to small delays. Three examples are given to illustrate these results.

Method and system for updating email addresses

Abstract: Embodiments of the present invention provide a network-based method and system for forwarding an email message to an updated email address. After a user changes his or her email address, the user sends information regarding the updated email address to an address-change server used in conjunction with the present invention. The address-change server stores the updated email information in its database. When a sender wants to reach a recipient whose email address has changed, the sender sends an email message to the address-change server. The address-change server forwards the updated email address to the sender. The sender's email program, modified in accordance with the present invention, programmatically forwards the sender's email message to the recipient's new email address.

Limitations and Countermeasures of PID Controllers

Abstract: It is well-known that PID controllers show poor control performances for an integrating process and a large time delay process. Moreover, it cannot incorporate ramp-type set-point change or slow disturbance. We discuss the above-mentioned limitations of the PID controller. Through the analysis of the limitations, simple techniques are developed to avoid these poor control performances and incapabilities. We introduce a control structure composed of two PID controllers to manipulate both the set-point change process and the input disturbance rejection process. A simple feedforward and feedback loop are proposed to treat a ramp-type set point and disturbance (low-frequency set point and disturbance). In addition, an internal feedback loop is introduced to incorporate integrating processes, and a tuning strategy using the model reduction is proposed to efficiently tune the controller for high-order processes. A dead-time compensator is used to manipulate a large time delay process more efficiently.

Multi-Loop opto-electronic microwave oscillator with a wide tuning range

Abstract: A versatile photonic radio frequency (RF) oscillator employs multiple feedback loops of different delay times, including at least one optical feedback loop, to generate RF signals with ultra low phase noise, narrow spectral linewidth, and a continuous wide tuning range of high resolution. Specifically, an electro-optical modulator and a long optical fiber loop are implemented in one dual-loop system. In addition, a light beam from a light source can be directly modulated by using feedback signals from multi feedback loops to alter the electrical control signal to the light source. Furthermore, the disclosed system supports both electrical and optical RF outputs. External optical injection and electrical injection can be implemented.

DC offset reduction in a transmitter

Abstract: A transmitter comprising at least first and second phase related signal paths, respective frequency up-converters, a combiner for combining the output of the respective frequency up-converters and for supplying the combined signal to a power amplifier. A feedback loop is provided which has a coupler for deriving a portion of the power amplifier output signal and supplying it to first and second phase related feedback paths. Each of the feedback paths comprises frequency down-converters. The dc offset is measured at the respective inputs of the frequency up-converters when the feedback around the linearization loop is reduced to zero without altering the dc offsets produced at the outputs of the frequency down-converters. Subtractors subtract the measured dc offsets from the feedback loop error signals.

Low drop-out voltage regulator having high ripple rejection and low power consumption

Abstract: A low drop-out regulator circuit that has high ripple rejection and low power consumption. A first local feedback loop is a high-speed, high-bandwidth loop that actively rejects noise from the input source to the regulator. A second feedback loop, having lower speed and a correspondingly lower bandwidth than the first feedback loop, regulates the output voltage. Each feedback loop is separately optimized for its respective bandwidth requirements and, therefore, the regulator is highly efficient. The first feedback loop comprises an amplifier and a pair of PMOS transistors configured as a current mirror with current gain. The first feedback loop generates a first current for charging an output capacitor. Feedback ensures that the first current is proportional to a second current generated by the second feedback loop while rejecting noise from the input source. The second feedback loop comprises a transconductance amplifier that controls the second current with feedback such that the first current charges the output capacitor to the desired output voltage level. The second loop has a lower bandwidth than the first loop because the bandwidth of the second feedback loop is dominated by a relatively large output capacitance and compensation capacitance, while the bandwidth of the first feedback loop is dominated by the relatively small gate capacitances of the pair of transistors and a relatively small compensation capacitance.

Robustness of Adaptive Unbalance Control of Rotors with Magnetic Bearings

Abstract: Rotor unbalance in the primary cause of unacceptable vibration in rotating machinery. Over the last decade, researchers have explored different methods of taking advantage of the active nature of magnetic bearings to attenuate unbalance response including both feedback and adaptive open loop methods. An important issue in the application of this technology to industrial machines is the robustness of the unbalance control algorithm. The stability and performance robustness of a promising adaptive open loop control algorithm is examined. Expressions are derived for a number of unstructured uncertainties. Experimental results are then presented, which evaluate the algorithm's robustness with respect to three variations: gain schedule errors, random additive errors, and feedback loop gain. The robustness exhibited in these tests was quite good and, along with the excellent vibration attenuation obtained, recommend the algorithm for further testing and industrial application. The experimental results indicate ...

Method and apparatus for oversampled, noise-shaping, mixed-signal processing

Abstract: A signal processing circuit is provided which includes a frequency selective network in a feedback loop for noise shaping purposes. A sampling analog-to-digital converter in the feedback loop operates at a sample frequency substantially above the Nyquist frequency. A switching device is driven by the sampling analog-to-digital converter and produces a continuous-time output signal which is continuously monitored by and fed back to the frequency selective network for noise and distortion correction in the feedback loop. This is in contrast to traditional techniques which employ only state feedback. State feedback (i.e., digital or sampled) of the output of the analog-to-digital converter may also be employed in combination with the continuous-time feedback of the switching device output.

Outcomes Assessment in Engineering Education

Abstract: Outcomes assessment is a method for determining whether students have learned, have retained, and can apply what they have been taught. Assessment plans have three components: a statement of educational goals, multiple measures of achievement of the goals, and use of the resulting information to improve the education process. The results of outcomes assessment are part of a feedback loop in which faculty are provided with information that they can use to improve both their teaching and student learning. The experience of the Department of Chemical Engineering at West Virginia University is used as an example of how an assessment plan is developed and implemented. Examples of multiple measures of student learning outcomes and how the resulting information is used are presented. The resulting feedback loop allows for corrections to be made in specific classes if deficiencies are found, and indicates when remedial action should be taken to ensure that students do not graduate until a minimum level of competency is achieved.

Programmable analog array and method for establishing a feedback loop therein

Abstract: A programmable analog array (10) comprises an array of configurable cells (11), each cell (11) including analog circuitry (12) and digital circuitry (14). The cells (11) are configured for a particular functional application. The digital circuitry (14) converts an analog signal generated by the analog circuitry (12) into digital control information, which is then used to adjust the analog circuitry (12). Therefore, the analog circuitry (12) and the digital circuitry (14) form a digital feedback loop. The digital feedback loop is established either within a single cell or among neighboring cells. Thus, the digital feedback loop is established without using a global data bus.

Multi-channel stabilization of a multi-channel transmitter through correlation feedback

Abstract: A correlation feedback method and apparatus for multi-channel stabilization of a multi-channel transmitter in which a single external receiver is used to detect the total power output from the multi-channel transmitter and to control each channel by correlating the total power output signal with channel data to measure the channels' signal power and control the output power via a feedback loop. The inventive system is suitable for use with and able to accommodate both integrated lasers and an array of discrete independent lasers; the system is also equally applicable for use with channels comprising random independent data or broadcast data.

Stability analysis of Cartesian feedback linearisation for amplifiers with weak nonlinearities

Abstract: RF amplifier linearisation by Cartesian feedback is analysed using a multiple input multiple output (MIMO) model. The effects of RF amplifier distortion, namely AM/AM and AM/PM distortion, are shown to degrade the stability of the Cartesian feedback loop. A versatile technique is presented that allows the amount of stability degradation to be determined for RF amplifiers provided distortion is not too large (i.e class A to class AB amplifiers). Loops with low stability margins are shown to exhibit out-of-band noise peaking. It is concluded from the noise analysis undertaken, that the highest proportion of gain possible should be placed ahead of the loop compensation to minimise out-of-band noise.

Feedback loop analysis for AC/DC rectifiers operating in discontinuous conduction mode

Abstract: High power factor rectifiers employing converters operating in discontinuous conduction mode (DCM) exhibit "automatic" current shaping and use output voltage feedback to regulate the output voltage. Analysis of this feedback control loop requires derivation of the control-to-output transfer function in the presence of the rectified AC source voltage. In this paper, linear, line frequency averaged control-to-output transfer functions are derived for some common DCM power converter based rectifier topologies. Also, a new control scheme is analyzed which provides open loop correction for the nonideal input current of the DCM boost power converter, giving it unity power factor. Finally, a simple method of providing "fast" output voltage regulation under transient conditions is introduced.

A voltage control strategy for current-regulated PWM inverters

Abstract: Alternative voltage control strategies for current-regulated PWM inverters are analyzed, including previously established feedforward and feedforward/feedback controllers and a newly proposed decoupling feedback control strategy. The steady-state and dynamic characteristics of each of these control methods are illustrated and compared for a selected inverter design. It is shown that the feedforward controller exhibits steady-state error and an undesirable overshoot of the output voltages during startup. The addition of a feedback loop eliminates the steady-state error and reduces the overshoot; however, the natural response is underdamped regardless of the choice of feedback gains. A decoupling feedback control strategy that eliminates the disadvantages of the feedforward and feedforward/feedback controllers is described. Using the decoupling feedback controller, it is possible to eliminate the steady-state error and place the closed-loop poles wherever desired. Moreover, if the closed-loop poles are selected appropriately, it is possible to eliminate the overshoot of the output voltages during startup transients.

On robust impact control via positive acceleration feedback for robot manipulators

Abstract: In this paper, a long outstanding problem, robust impact control and force regulation with guaranteed stability is solved by adding a novel positive acceleration, feedback to the feedback loop in the direction of impact and force control for robot manipulators working in an unknown environment. A quick and stable transition can be accomplished with a nonzero impact velocity, and the transient force response can be controlled with minimum impact forces and minimum bouncing. In addition, a switching control strategy is designed to guarantee the stability of the impact control. Unexpected bouncing can be eliminated after finite switches. The output force and motion can be regulated simultaneously with high accuracy after contact is established. Rigorous stability analysis based on the Liapunov-like method is presented for the proposed control scheme. The control scheme was implemented and tested on a 6 DOF PUMA 560 robot arm. The experimental comparisons with other force control strategies were given to demonstrate the advantage of the proposed method. The result obtained in this paper can be applied to any system requiring impact control and force regulation.

Fast attack automatic gain control (AGC) loop for narrow band receivers

Abstract: A fast attack Automatic Gain Control (AGC) loop (100) having a first feedback loop with selectable responses shapes and a second feedback loop with selectable responses shapes Response shape selection is based, in part, upon fast pull-down, overshoot recovery, and normal mode loop operation

Driving scheme for minimizing ignition flash

Abstract: A ballast for powering a lamp at deep dim levels. Driving circuitry includes a feedback loop which compares a desired dim level to a signal representing actual lamp power consumption. The loop is closed once the signal representing actual lamp power consumption equals the desired dim level. During ignition, a switch in response to the lamp voltage reaching or exceeding a predetermined threshold opens the feedback loop. The feedback loop is closed once the lamp has been ignited. By closing the loop as soon as the lamp has been ignited, ignition flash is minimized.

An approach to fully differential circuit design without common-mode feedback

Abstract: Fully differential transconductance structures allow for greater linearity than their single-ended counterparts. The disadvantage is the need for common-mode feedback circuitry, which complicates the design and introduces additional design problems and constraints. In this paper we present and analyze a new technique for designing fully differential transconductance structures which removes the need for common-mode feedback by instead forming two independent nonlinear transconductance blocks, each of whose common-mode output voltage is well defined by the differential feedback.

Linearization of RF Power Amplifiers

Abstract: Linearization of RF power amplifiers is surveyed, reviewed and analyzed. Cartesian feedback is specifically presented as an effective means of linearizing an efficient yet non-linear power amplifier. This reduces amplifier distortion to acceptable levels and enables the transmission of RF signals utilizing spectrally efficient linear modulation schemes with a lower consumption of DC power. Results from constructing experimental hardware shows an intermodulation distortion (IMD) reduction of 44dB (achieving a level of -62dBc) combined with an efficiency of 42% when transmitting A°/4 QPSK. The careful amplifier characterization measurement method presented predicts performance to within 2dB (IMD) and 4% (efficiency) of practical measurements when used in simulations. A comprehensive stability analysis is developed using piecewise amplifier models within a multiple-input, multiple-output block diagram representation of the cartesian feedback loop. The analysis shows how RF amplifier non-linearity, the RF phase adjuster setting, loop gain, bandwidth and delay affect stability. A graphical interpretation of the analysis is given that indicates how stable a given RF amplifier will be when setting up a practical cartesian feedback loop. Instability is shown to result when the amount of RF phase rotation introduced by AM/PM distortion, and by setting error in the RF phase adjuster within the loop, equals the open-loop phase margin. For one of the amplifiers investigated, the analysis predicts that instability results just after the transistor turn-on region when the phase adjuster is adjusted above optimum, and instability also results at transistor saturation when adjusted lower than optimum. This is also demonstrated with experimental hardware. From the analysis, the perturbated behaviour of the non-linear piecewise amplifier model is shown to display two forms of operation when placed in a feedback loop, namely: spiral mode and stationary mode. Spiralling tends to cause the noise floor of the output spectrum to rise on one side depending on the direction of the spiral. The direction is in turn dependent on the setting of the RF phase adjuster within the loop. When the phase adjuster is in the forward path, phase adjustments lower than optimum, will cause the noise to rise on the right side of the output spectrum (anti-clockwise spiralling) and viceversa. With the phase adjuster in the feedback path the reverse is true. Loops with low stability margins are demonstrated to exhibit closed-loop peaking which can affect the out of band noise performance of a cartesian feedback transmitter. In order to achieve a non-peaking condition for a first order loop with delay, the phase margin of the loop needs to be around 60°. It is also possible to approximately predict the degree of peaking from the gain and phase margins. Further investigation of noise performance suggests the loop compensation should be placed as far up the forward chain as possible (i.e. close to the power amplifier) in order to minimize the out-of-band noise floor. This too is demonstrated experimentally. The concept of dynamic bias is also presented as a method to improve cartesian feedback efficiency. The method works by setting up optimum bias conditions for the power amplifier (derived from amplifier characterizations) and then having the cartesian feedback loop make fine adjustments to the RF drive to achieve the exact required output. This way the bias conditions do not have to be applied perfectly, implying simple (i.e low switching frequency) switched mode power supplies can be used to apply the desired collector voltage for example. The simple step-down switch mode power supply constructed achieved an efficiency of 95% at high output levels. Applying it to a cartesian feedback loop markedly improved efficiency. At an output power of 20dBm average, the linearized amplifier efficiency lifted from 45% to 67%, an improvement of over 20% and a reduction in current consumption by 33%.

Active resistor for stability compensation

Abstract: An active termination resistor is provided within a feedback loop circuit thus advantageously increasing the stability of the feedback loop circuit. In particular, the active termination resistor traces the impedance of the feedback loop such that R(f) = 1/GM3(f). The active resistor may also be configured to track the value of the resistor to set the feedback transconductance over process and temperature variations to ensure stability of the feedback loop over these variations.

Low power ΔΣ convertor

Abstract: A low power passive ΣΔ converter for baseband applications and with a built in mixer for direct conversion. For direct conversion, low power consumption is achieved by adopting a passive loop filter for the ΣΔ converter together with merging the sampling and mixing functions together utilizing a specially designed mixer. With a passive loop filter, the only gain element in the loop is a high gain, high speed, low noise comparator. The mixer can be located outside of the feedback loop, although according to one aspect of the present invention, the mixer is incorporated inside the feedback loop. For baseband applications, the same design is utilized with a simple sampling switch instead of a mixer for processing baseband signals with low power consumption.

Jitter reduction through feedback for picosecond pulsed InGaAsP lasers

Abstract: Following a comparison of picosecond-pulse generation techniques, feedback schemes are reported for the generation of picosecond pulse trains with improved jitter for both multicontact and conventional single-contact InGaAsP-InP lasers. Subpicosecond jitter is achieved for Q-switched laser sources using a novel optoelectronic feedback scheme. The use of resonant electrical feedback is shown to improve the timing jitter of gain-switched pulses by up to six times. Pulse-to-pulse timing jitter as low as 250 fs is demonstrated for a hybrid of optical and electrical feedback schemes. Limits for timing jitter in diode lasers are established for optoelectronic, electrical, and optical feedback schemes, and the key picosecond pulse generation schemes are compared in terms of timing jitter for the first time.

Analysis and simulation of digitally-controlled grid-connected PWM-converters using the space-vector average approximation

Abstract: A technique to evaluate the dynamic performance of control principles for PWM-converter systems is presented. In the modelling of vector-controlled, grid-flux-oriented control systems, nonlinear switches and time-varying elements due to coordinate transformation occur in the feedback loop. By using space-vector averaging, coordinate transformations and nonlinear switches are avoided. A linear time-invariant analytical model in the grid-flux-oriented dq-frame is derived. Simulations with a switched PWM-model and an analytical model show accurate transient response and frequency response.

Artificial neural network feedback loop with on-line training

Abstract: In this paper, we discuss the implementation of a neural network feedback loop, a state estimator and a state feedback controller, that trains online to overcome variations between the a priori model dynamics and the true system dynamics. The technique uses the previously developed neuro-observer, an extended Kalman filter augmented with a neural network, and a model reference adaptive control law. Both neural networks, the state estimator's and the controller's, are trained using extended Kalman filter training paradigms. The paper also includes a discussion of parameter selections for the neural networks and their training paradigms.