Proportional-integral Compensator Research Articles

Modular Current Sharing Control Scheme for Parallel-Connected Converters

A modular current sharing control scheme is proposed in this paper to attain good current distribution between equally rated parallel-connected converters. In this scheme, local information is used by each inverter to achieve the required current control with minimal information sharing between the converters. Unlike conventional current sharing control methods that use a stationary or rotating reference frame representation, the converter currents in the proposed controller are represented by the magnitude of the current space vector. As a result, each converter employs only one proportional-integral compensator to share the load current. The operation of the new current sharing control scheme is demonstrated using two different pulsewidth modulation (PWM) control strategies: conventional space-vector PWM and discontinuous PWM. A mathematical analysis of the proposed control scheme is presented, and the performance of the controller is experimentally verified using a 2.5-kVA test rig. The results show excellent current sharing characteristics with minimal communications between the parallel-connected converters.

Control strategy and hardware implementation for DC–DC boost power circuit based on proportional–integral compensator for high voltage application

For high-voltage (HV) applications, the designers mostly prefer the classical DC–DC boost converter. However, it lacks due to the limitation of the output voltage by the gain transfer ratio, decreased efficiency and its requirement of two sensors for feedback signals, which creates complex control scheme with increased overall cost. Furthermore, the output voltage and efficiency are reduced due to the self-parasitic behavior of power circuit components. To overcome these drawbacks, this manuscript provides, the theoretical development and hardware implementation of DC–DC step-up (boost) power converter circuit for obtaining extra output-voltage high-performance. The proposed circuit substantially improves the high output-voltage by voltage-lift technology with a closed loop proportional–integral controller. This complete numerical model of the converter circuit including closed loop P-I controller is developed in simulation (Matlab/Simulink) software and the hardware prototype model is implemented with digital signal processor (DSP) TMS320F2812. A detailed performance analysis was carried out under both line and load regulation conditions. Numerical simulation and its verification results provided in this paper, prove the good agreement of the circuit with theoretical background.

Error Amplifier Design of Peak Current Controlled (PCC) Buck LED Driver

A discrete time-domain modeling and analysis for the peak current controlled (PCC) buck light-emitting diode (LED) driver is presented in this paper. The discrete time-domain equa- tion representing the buck LED driver is derived and linearized about the equilibrium state. Also the switching control law, the proportional-integral compensator is used here as an example of the error amplifier, is linearized about the equilibrium state. The linearized buck LED driver and the control law are then combined to arrive at a linearized PCC buck LED driver. The root-locus method is employed to analyze the closed-loop system. The design guidelines and experimental results for the PCC buck LED driver are presented. Index Terms—Buck light-emitting diode (LED) driver, discrete time-domain modeling, error amplifier design, root-locus stability analysis.

Tuning of reset proportional integral compensators with a variable reset ratio and reset band

The PI+CI compensator, given by the parallel connection of a proportional integral (PI) compensator and a Clegg integrator (CI), has been shown to be effective in a number of practical applications, overcoming fundamental limitations of PI compensation. Two key design aspects of PI+CI compensation is the use of the resetting law (zero crossing/reset band) and a (constant/variable) reset ratio; these two design factors have been previously used in control practice, but using heuristic design methods. This work develops a systematic design method for the tuning of reset PI compensators, specifically for first- and second-order plants, obtaining in both cases simple tuning rules. In addition, several detailed examples are developed; therefore, a detailed analysis of cost of feedback and robustness again parametric uncertainty is also given. Finally, an experiment of pH In-Line control is made to show the advantages of the proposed tuning rule.

Simplified procedure for controlling pressure distribution of a scramjet combustor

Scramjet engines are used at extreme temperatures and velocity. New control problems involving distributed parameter control have been found concerning investigations of the control of scramjet engines whose physical states are spatially interacted. Succeeding the existing theoretical studies on the distributed parameter control for scramjet engines, this paper puts forward a simplified distributed parameter control approach for scramjet engines aimed at engineering application. The simplified control procedure uses the classical proportional-integral (PI) compensation to control the target pressure distribution of scramjet engines, which is effective and applicable for practical implements. Simulation results show the validation of the simplified distributed parameter control procedure.

Combined pole assignment and mean value engine model multivariable decoupling control

This article considers a combined pole assignment and multivariable decoupling control algorithm using discrete-time, non-minimum state space (NMSS) methods. In contrast to earlier research based on low-order linear models, the approach is applied to a nonlinear mean value internal combustion engine model with three control inputs, namely the throttle plate angle, injected fuel mass flow and spark advance angle. The controlled outputs are the air mass flow pressure, crank shaft speed and air–fuel ratio (AFR). It is well known that, for example, regulating the AFR to the stoichiometric value (i.e. [Formula: see text]) leads to a desirable balance between power output and fuel consumption, while reducing pollutant emissions. In this regard, the linear NMSS approach is straightforward to design for a range of performance requirements and yields comparable results to a more complex benchmark sliding mode control system. Furthermore, it retains a similar implementation structure to current production units, which are typically based on conventional proportional-integral compensation. The robustness to changing operating levels and disturbances, including an air leakage signal, are evaluated in simulation.

Preliminary Attitude Control Studies for the ASTER Mission

This work discusses an attitude control study for the ASTER mission, the first Brazilian mission to the deep space. The study is part of a larger scenario that is the development of optimal trajectories to navigate in the 2001 SN263 asteroid system, together with the generation of orbit and attitude controllers for autonomous operation. The spacecraft attitude is defined from the orientation of the body reference system to the Local Vertical Local Horizontal (LVLH) of a circular orbit around the Alpha asteroid. The rotational equations of motion involve the dynamic equations, where the three angular speeds are generated from a set of three reaction wheels and the gravitational torque. The rotational kinematics is represented in the Euler angles format. The controller is developed via the linear quadratic regulator approach with output feedback. It involves the generation of a stability augmentation (SAS) loop and a tracking outer loop, with a compensator of desired structure. It was chosen the feedback of the p, q and r angular speeds in the SAS, one for each reaction wheel. In the outer loop, it was chosen a proportional integral compensator. The parameters are tuned using a numerical minimization that represents a linear quadratic cost, with weightings in the tracking error and controls. Simulations are performed with the nonlinear model. For small angle manoeuvres, the linear results with reaction wheels or thrusters are reasonable, but, for larger manoeuvres, nonlinear control techniques shall be applied, for example, the sliding mode control.

Design of a Self-Oscillating PWM Signal Generator With a Double Integration Loop

A novel digital self-oscillating pulse width modulation (PWM) signal generator with a hysteresis comparator is proposed in this study. The proposed generator, referred to as a “2nd-order PWM signal generator” in this paper, utilizes a double integration loop based upon the concept of delta-sigma modulation for precise conversion. A simple 2nd-order PWM signal generator was initially investigated, but it was found to exhibit impractical behavior: the period of the PWM output signal increased slowly with time. An analysis of the limit cycle state of this simple generator using describing function theory shows that the amplitude of the limit cycle is extremely large. Proportional integral (PI) compensation is therefore used to adjust the limit cycle state by varying the proportional gain and the coefficient of the integral. The use of PI compensation suppresses the amplitude of the limit cycle, thus making the 2nd-order PWM signal generator practical. An analysis of this modified generator reveals that the period of the PWM signal can be controlled by the hysteresis width of the comparator and by the proportional gain. As a test case, a switching frequency of 300 kHz is used for the performance evaluation of the proposed PWM signal generator with a sampling frequency of 12.5 MHz. A noise-shaped output is obtained, and a high-precision, ultra-low-distortion PWM signal with a high effective duty cycle resolution is achieved.

Simulation and control based on temperature measurements for Petlyuk distillation columns

ABSTRACTThis paper presents a control strategy based on stage temperature measurements to control composition of the products in a Petlyuk‐type distillation column. This column is formed by a prefractionator in which feed is introduced and a main column from which three product streams are extracted. Prefractionator and main‐column modules are connected through the exchange of liquid and vapor streams resulting in a strong interaction that can result in operating problems, poor control performance, and instability due to their complex structure. Different steady‐state methods for the selection of appropriate control structures were analyzed. The control structure comprises four controllers implemented as follows: three Proportional‐Integral (PI) controllers to regulate the temperature of three stages along the main column and a cascade controller to regulate temperature at a stage in the main column manipulating temperature in a prefractionator stage. Controllers were designed using internal model control guidelines for traditional PI compensation. Feed composition disturbances were introduced in order to observe the response of the control system. The obtained results show that the control structure maintains the purity of the final products within acceptable ranges despite the existence of disturbance. Copyright © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

Wind Turbine Generation System With Optimized DC-Link Design and Control

This paper presents an optimized capacitance design for the dc link of a back-to-back converter for wind turbine power generation. The design method combines switching ripple and dynamic specifications to give the smallest possible dc-link capacitance and the required proportional-integral compensator for the voltage regulation. Furthermore, a novel concept to globally manage the on/off switching of back-to-back power subconverters, based on a finite-state machine, is presented. The proposed management system keeps control of the dc-link voltage for proper operation of both subconverters regardless of wind or grid conditions.

System Identification and Closed-Loop Control of End-Tidal CO<formula formulatype="inline"><tex Notation="TeX">$_{\bf 2}$</tex></formula> in Mechanically Ventilated Patients

This paper presents a systematic approach to system identification and closed-loop control of end-tidal carbon dioxide partial pressure (PETCO2) in mechanically ventilated patients. An empirical model consisting of a linear dynamic system followed by an affine transform is proposed to derive a low-order and high-fidelity representation that can reproduce the positive and inversely proportional dynamic input-output relationship between PETCO2 and minute ventilation (MV) in mechanically ventilated patients. The predictive capability of the empirical model was evaluated using experimental respiratory data collected from eighteen mechanically ventilated human subjects. The model predicted PETCO2 response accurately with a root-mean-squared error (RMSE) of 0.22+/-0.16 mmHg and a coefficient of determination (r2) of 0.81+/-0.18 (mean+/-SD) when a second-order rational transfer function was used as its linear dynamic component. Using the proposed model, a closedloop control method for PETCO2 based on a proportionalintegral (PI) compensator was proposed by systematic analysis of the system root locus. For the eighteen mechanically ventilated patient models identified, the PI compensator exhibited acceptable closed-loop response with a settling time of 1.27+/- 0.20 min and a negligible overshoot (0.51+/-1.17%), in addition to zero steady-state PETCO2 set point tracking. The physiologic implication of the proposed empirical model was analyzed by comparing it with the traditional multi-compartmental model widely used in pharmacological modeling.

INSTABILITIES IN DIGITALLY CONTROLLED VOLTAGE-MODE SYNCHRONOUS BUCK CONVERTER

In this paper, instabilities and bifurcation behavior in a DC–DC digitally controlled voltage-mode synchronous buck converter (SBC) are studied. The bifurcation diagram of the system under a proportional-integral (PI) compensation is presented. Following the system mathematical description in the continuous time domain, the z-domain pulse transfer function is derived in terms of system parameters. The stability range of the design parameter is obtained in closed form by using the Jury test combined with the describing function (DF) method. Experimental measurements from a laboratory prototype are used to validate the theoretical predictions and the numerical simulations.

Flow Control of Methane Fermentation Digested Sludge Applicator

A digested sludge fertilizer applicator was designed and developed to apply concentrated methane digested sludge in a paddy field. The applicator was mounted on a high-clearance vehicle to apply the fertilizer as top-dressing at panicle initiation of rice. It employs three electric-motor-drive pumps to control the flow rate of the digested sludge. The pumps dispense the concentrated digested sludge at 4-15 kg/min. The rotational speed of the pump is controlled by a proportional-integral (PI) compensator with a feedback based on its rotational speed and a pre-filter of the desired rotational speed. The fertilizer applicator was tested using the concentrated digested sludge fertilizer in actual farm work. The error in the application rate was found to be −4.4%. The developed applicator was able to apply digested sludge fertilizer at a reliably uniform rate in the paddy field.

Two Alternative Modeling Approaches for the Evaluation of Wind Farm Active and Reactive Power Performances

Based on the stator-flux-oriented electromechanical model of a doubly fed induction machine (DFIM), this paper presents two different approaches to wind farm modeling. Particularly, the overall control system of the DFIM is modeled in detail, so that tuning equations that allow adjusting the parameters of its proportional-integral (PI) compensators straightforwardly are provided. In addition to validating the wind generator model proposed, experimental tests carried out on a 660-kW doubly fed induction generator (DFIG) prove that such a control system makes it possible to govern separately its stator-side or net active and reactive powers. The two wind farm models proposed, which are assumed to be made up of DFIM type generators exclusively, are mainly devised to assist the design and test of closed-loop control algorithms for the wind farm total power factor. They generally imply significantly different computational loads, so that the second may be regarded as a simplified version of the first one. The net active and reactive power performances of both wind farm models are finally compared via simulation, which allows identifying the stronger and weaker points associated to each model

Multiple harmonics control for three-phase grid converter systems with the use of PI-RES current controller in a rotating frame

Voltage source inverters connected to the grid in applications such as active rectifiers, active filters, uninterruptible power supplies, and distributed generation systems need an optimal ac current control. To obtain zero steady-state error at the fundamental frequency (i.e., unity power factor), the use of a standard integrator in a rotating frame is as effective as the use of a resonant controller in a stationary frame. However, the grid voltage harmonics influence the current controller and generate current harmonics unless several integrators in multiple rotating frames or resonant compensators in a stationary frame are adopted. In this letter, a hybrid system consisting of a proportional integral (PI) controller plus a generic hth harmonic resonant controller implemented in a frame rotating at the n th harmonic frequency is discussed in detail. The hth harmonic controller is able to decrease both the (h - n)th and (h + n)th harmonics, while the PI controller is able to decrease other harmonics if the synchronization phase signal adopted for the frame transformation is unfiltered. It is demonstrated that the use of a PI and sixth harmonic resonant compensator is effective for both positive and negative sequence fifth and seventh harmonics; hence, four harmonics are compensated with the proportional integral-resonant (PI-RES) controller implemented in a synchronous frame. Simulation and experimental tests validate the proposed analysis

Current Distribution Control Design for Paralleled DC/DC Converters Using Sliding-Mode Control

This paper shows the analysis and design of a parallel-connected converter system using sliding mode control techniques. The design is particularised for a system that consists of N boost converters and a current feedback loop based on a proportional-integral compensator of the output voltage error. The paper emphasises the advantages of the sliding-mode control over the classic design method based on small-signal models, thus providing an effective and robust means of controlling nonlinear multi-input converters. The design is based on the Utkin conditions, which permit us to know the regions under which a sliding mode exists. This fact allows us to design the compensator and to introduce some modifications in the control loop that avoids input-current overshoots during the system startup. Simple design expressions are obtained and verified with simulation and experimental results, thus showing the improvements achieved with the proposed modifications.

Adaptive Observer for Sensorless Control of Permanent Magnet Synchronous Motor Drives

This paper develops a sensorless control method for nonsalient permanent magnet synchronous motor drives. The position and speed estimations are based on the back electromotive force (emf) estimation in f g stator reference. Two equivalent solutions are developed to estimate the back emf (i.e., the adaptive filter technique), and alternatively, an extended disturbance observer, both being speed adaptive. The position estimation is computed directly from the back emf components. The speed estimation uses a model reference adaptive observer as a sinusoidal oscillator external synchronized by the back emf with (i) an amplitude adaptive correction speed depending, and (ii) a phase correction realized by an adaptive mechanism using a variable structure plus a proportional integral compensator. The speed sign is included. The speed and position observers can be independently tuned, and the estimations are robust to parameter deviations. A relatively large speed range of 1:100 is obtained. Extensive simulation results are given and discussed.

Approximations in compensator design: A duality

In classical controller design, poles far to the left of dominant poles are sometimes ignored. Similarly, in some proportional-integral compensation techniques, the controller zero is placed close to the origin and design proceeds after cancelling this zero with a pole at the origin. A rigorous basis for these methods is provided, it being shown that there is a duality between the two.

DC Thruster Controller Implementation with Integral Anti-wind up Compensator for Underwater ROV

This paper presents the implementation and experimental results of different conventional position control schemes for positioning an experimental model, the THETIS Underwater Remotely Operated Vehicle (UROV). To achieve minimum response time and in order to avoid the so-called Integral Wind-up phenomenon, Proportional-Integral (PI) plus integral antiwind-up compensation is used. Hardware implementation of the design is described and experimental results of a digital position control system over one direction using two dc thrusters fed by four quadrant (PWM-Driven) transistor choppers are given. All control algorithms are implemented using a TI‘s Digital Signal Processor (DSP). The actual position and orientation of the vehicle in a 3-D space is derived through a combination of an ultrasonic scanning system, a direction gyrocompass, and a pressure depth sensor. The vehicle‘s use at the present stage of development is to perform water pollution measurements.

Robust beam-pointing and attitude control of a flexible spacecraft

This paper studies the problem of simultaneously controlling the communications beams and the attitude angles of the main bus of a flexible spacecraft. The controller is a multivariable proportional-integral compensator augmented by a Kalman filter. Two design methods have been explored: the first method is based on eigenvalue analysis, while the second makes use of singular value criteria. Both approaches result in a controller that is robust in the presence of the residual modes omitted from the design model. The singular value method, however, is shown to be far more conservative than the eigenvalue method.