Optimal Transient Performance Research Articles

Design of auto‐tuning‐based adaptive controllers for voltage source converters with inductive loads

AbstractThis paper presents an auto‐tuning method for dc‐ac voltage source converters (VSCs) with an inductive load that is based on the modified relay feedback test (MRFT). Controllers tuned by the proposed method can produce near‐optimal dynamic performance for dc–ac VSCs without requiring knowledge of the plant's parameters. The controller consists of a PID cascaded with a digital notch filter. The tuning involves two steps. In the first step, the MRFT is used to tune the digital notch filter to compensate for the LCL resonance resulting from the LC filter's interaction with the inductive load. In the second step, one more MRFT is used to tune the PID controller using optimal tuning rules that are derived in advance (offline). The proposed optimal for the class of the dc–ac VSCs tuning rules can guarantee a specified phase margin and near optimal transient performance for any randomly picked VSC. The performance of the proposed tuning of the PID + notch filter is verified by simulations and experiments. The dynamic response of the auto‐tuned controller compares well to the response of a theoretically optimal but non‐auto‐tuned PID + notch filter designed using the full knowledge of the LC filter and the load.

Gradient-Based Predictive Pulse Pattern Control of Medium-Voltage Drives—Part II: Performance Assessment

In this article, the performance of gradient-based predictive pulse pattern control (GP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> C) is evaluated for a medium-voltage variable-speed drive consisting of a three-level neutral-point-clamped (NPC) inverter and a medium-voltage induction machine. To this end, real-time tests are performed in a hardware-in-the-loop (HIL) environment, which, along with extensive simulation studies, elucidate the potential of performance gains achieved with GP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> C. As shown, by manipulating offline-computed optimized pulse patterns (OPPs) in real time such that the stator current of the machine follows a precalculated optimal current trajectory, superior steady-state and transient performance can be achieved. Specifically, the current total demand distortion (TDD) is significantly reduced compared with established control methods, such as field-oriented control (FOC) with space vector modulation (SVM), while shorter settling times during transients are achieved. Finally, to complete the assessment of the control method of interest, real-time implementation aspects are discussed in detail.

Multichannel sequential display LED driver with optimal transient performance and efficiency via synchronous integral control

This study proposes a high performance multichannel sequential display light emitting diode (LED) driver with pulse width modulated dimming control. A synchronous integral control strategy is developed for achieving optimal transient performances for the channel voltages and ideal rectangular waveforms for the LED current, which will help to maintain high efficiency and extend the lifetime of the LEDs. By synchronous integral control, each channel has a corresponding integrator whose input and output are turned on and off synchronously with the LED string. The proposed driver topology and control strategy are supported by detailed analysis on stability and transient response during on-time interval of a channel by using the averaged state-space model. The effectiveness of the design method is demonstrated with simulation. A three-channel LED driver is constructed to experimentally validate the high efficiency and high performance of the proposed topology and control strategy with desired LED current waveform and nearly constant channel voltages.

Auxiliary bridge arm–based switching control for optimal unloading transient performance of multiphase buck converters

SummaryFor a low‐conversion ratio buck converter, the step‐down (unloading) transient lasts much longer than the step‐up transient for the same change of the load. Regarding this issue, an auxiliary bridge arm (ABA) multiphase buck converter with switching control scheme is proposed for the optimal unloading transient performance. With the ABA, the input voltage is reversely connected into the inductor current freewheeling loop during the unloading transient. In this case, the fall slew rate of the inductor current increases, because of the voltage across the inductor increase. Meanwhile, the capacitor‐charge balance theory is used to calculate the switching moment and achieve the minimum settling time and the voltage overshoots. Finally, a 12‐ to 3.3‐V two‐phase synchronous buck converter prototype is built. The experimental results show that the settling time and the voltage deviation are both improved over 50% compared with that of the average current sharing scheme and the time‐optimal control scheme.

An Agile Supply Modulator With Improved Transient Performance for Power Efficient Linear Amplifier Employing Envelope Tracking Techniques

This article presents an agile supply modulator with optimal transient performance that includes improvement in rise time, overshoot and settling time for the envelope tracking supply in linear power amplifiers. For this purpose, we propose an on-demand current source module: the bang–bang transient performance enhancer (BBTPE). Its objective is to follow fast variations in input signals with reduced overshoot and settling time without deteriorating the steady-state performance of the buck regulator. The proposed approach enables fast system response through the BBTPE and an accurate steady-state output response through a low switching ripple and power efficient dynamic buck regulator. Fast output response with the help of the added module induces a slower rise of inductor current in the buck converter that further helps the proposed system to reduce both overshoot and settling time. This article also introduces an efficient selective tracking of envelope signal for linear PAs. To demonstrate the feasibility of the proposed solution, extensive simulations and experimental results from a discrete system are reported. The proposed supply modulator shows 80% improvement in rise time along with 60% reduction in both overshoot and settling time compared to the conventional dynamic buck regulator-based solution. Experimental results using the LTE 16-QAM 5 MHz standard shows improvement of 7.68 dB and 65.1% in adjacent channel power ratio (ACPR) and error vector magnitude (EVM), respectively.

Transient modeling and simulation of a nonisothermal sodium–sulfur cell

The use of sodium-sulfur batteries at the grid level requires high current density operation that can cause cell deterioration, leading to lower sulfur utilization and lower energy efficiency. In addition, it can result in undesired thermal runaway leading to potentially hazardous situations. A rigorous, dynamic model of a sodium-sulfur battery can be used to study these phenomena, design the battery for optimal transient performance, and develop mitigation strategies. With this motivation, a first-principles, fully coupled thermal-electrochemical dynamic model of the entire sodium-sulfur cell has been developed. The thermal model considers heat generation due to Ohmic loss, Peltier heat, and heat due to entropy change. Species conservation equations are written in the sulfur electrode by considering the phase transition and change in the composition depending on the SOD. Species conservation equations are written in the beta”-alumina electrolyte for the ionic species by considering the change in composition due to diffusion and migration. In addition, the potential distribution, and cell resistance for this spatially distributed system has been modeled. Furthermore, temperature-dependent correlations for the physicochemical properties are developed. The model is used to study both charging and discharging characteristics of the cell at varying current densities.

Advanced Constraints Management Strategy for Real-Time Optimization of Gas Turbine Engine Transient Performance

Motivated by the growing technology of control and data processing as well as the increasingly complex designs of the new generation of gas turbine engines, a fully automatic control strategy that is capable of dealing with different aspects of operational and safety considerations is required to be implemented on gas turbine engines. An advanced practical control mode satisfaction method for the entire operating envelope of gas turbine engines is proposed in this paper to achieve the optimal transient performance for the engine. A constraint management strategy is developed to generate different controller settings for short-range fighters as well as long-range intercontinental aircraft engines at different operating conditions by utilizing a model predictive control approach. Then, the designed controller is tuned and modified with respect to different realistic considerations including the practicality, physical limitations, system dynamics, and computational efforts. The simulation results from a verified two-spool turbofan engine model and controller show that the proposed method is capable of maneuverability and/or fuel economy optimization indices while satisfying all the predefined constraints successfully. Based on the parameters, natural frequencies, and dynamic behavior of the system, a set of optimized weighting factors for different engine parameters is also proposed to achieve the optimal and safe operation for the engine at different flight conditions. The paper demonstrates the effects of the prediction length and control horizon; adding new constraints on the computational effort and the controller performance are also discussed in detail to confirm the effectiveness and practicality of the proposed approach in developing a fully automatic optimized real-time controller for gas turbine engines.

An adaptive integral sliding mode control approach for piezoelectric nano-manipulation with optimal transient performance

This paper presents a control framework supporting high precision tracking of a piezoelectric nano-manipulating system with guaranteed transient performance, where a modified dynamic model describing the hysteresis behavior is also proposed. To achieve the desired optimal transient performance, a dynamic hysteresis compensation based control approach is developed by employing robust adaptive integral sliding mode control technique to accommodate both hysteresis nonlinearities and model uncertainties. An adaptive law is designed to estimate the gain of the integral sliding mode controller such that the chattering behavior is alleviated and the upper bound of uncertainties is no longer required a priori. In particular, it can be proved that the tracking error converges to zero in a finite time. The proposed control architecture is applied to a PZT actuated nano-manipulating stage, where real time implementations demonstrate excellent tracking performance with tracking error around 4.6‰for multi-frequency trajectory tracking experiments. Comparisons with existing results are also given, where significant improvements are achieved in various tracking scenarios.

Evaluation of CES and DFIG unit in AGC of realistic multisource deregulated power system

Summary This article discusses evaluation of dynamic contribution of wind turbine unit of doubly fed induction generators (DFIGs) type and capacitive energy storage (CES) in frequency regulation services in 2-area interconnected power system, having diverse thermal-hydro-gas (T-H-G) generating units in deregulated power environment. To obtain optimal dynamic responses of area's frequency oscillations following a small load perturbation, CES/DFIG units have been included in both control areas in coordination with thyristor controlled phase shifter (TCPS).The behavior of DFIGs to enhance dynamic performances of the proposed power system has been investigated by providing inertial support through modified inertial control scheme. The control scheme responds proportionally to frequency variations due to sudden load changes in the power system and uses wind turbine's kinetic energy to provide the inertial control support under several operational conditions. The gain parameters of the integral controller is obtained by using integral square error technique. The performance of the proposed system has been examined in different contract scenarios. Results show that the coordinated action of CES/DFIG units with TCPS unit provide optimal transient performance by arresting the initial dip in area frequencies as well as the power flow deviation in tie-line between the 2 areas. Further, analysis reveals that CES unit response is better and quicker than DFIG unit to damp the system oscillations.

Hardware Implementation of Shunt APF Using Modified Fuzzy Control Algorithm with STM32F407VGT Microcontroller

This article presents a modified fuzzy controller (MFC) to generate a reference signal for the control algorithm to drive the shunt active power filter (SAPF) for improving the power quality of a microgrid at the distribution end. The proposed MFC, based on the alive-and-kicking behavior of the system, is used to regulate the DC-link voltage of the SAPF. The MFC is implemented through the general dynamic behavior of a process with introducing the new rules set. It is compared with the PI controller for evaluation of optimal steady-state, dynamic, and transient performance of SAPF, namely the reactive power and DC voltage control. The effectiveness of the proposed controller is tested on non-linear loads using a hardware prototype. The STM32F407VGT (ARM Ltd., San Jose, California, USA) processor is used to interface algorithm with the hardware setup. The results of the proposed controller scheme are promising and are compared with MATLAB (The MathWorks, Natick, Massachusetts, USA) simulation results. The system is capable for minimizing current harmonics, reactive power and improving the power factor. Also, the advantage of the STM32F407VGT over the Digital Signal Processor (Texas Instruments, USA) is introduced. The performance of the proposed controller is better in comparison with conventional controller.

Transient Performance Improvement in the Boundary Control of Boost Converters using Synthetic Optimized Trajectory

This paper focuses on an improvement in the transient performance of Boost converters when the load changes abruptly. This is achieved on the basis of the nature trajectory in Boost converters. Three key aspects of the transient performance are analyzed including the storage energy change law in the inductors and capacitors of converters during the transient process, the ideal minimum voltage deviation in the transient process, and the minimum voltage deviation control trajectory. The changing relationship curve between the voltage deviation and the recovery time is depicted through analysis and simulations when the load suddenly increases. In addition, the relationship curve between the current fluctuation and the recovery time is obtained when the load suddenly decreases. Considering the aspects of an increasing and decreasing load, this paper proposes the transient performance synthetic optimized trajectory and control laws. Through simulation and experimental results, the transient performances are compared with the other typical three control methods, and the ability of proposed synthetic trajectory and control law to achieve optimal transient performance is verified.

Design optimisation of PID controller in automatic voltage regulator system using teaching-learning based optimisation algorithm

It is becoming increasingly difficult to ignore the role of the optimal design of the proportional-integral-derivative (PID) controller in achieving a satisfactory response in the automatic voltage regulator (AVR) system. The main aim of this paper is to determine the optimal gains of a PID controller in the AVR system using teaching-learning based optimisation (TLBO) algorithm. Linearly decreasing inertia particle swarm optimisation (LDIPSO) is also employed for comparison purposes. The simulation results are provided to compare the effectiveness of these two different algorithms. MATLAB toolboxes are employed in this paper. Simulation results show that the TLBO algorithm has a considerable potential when compared to one of the best-known heuristic algorithms for optimisation problems. It proves to be more robust than PSO in performing optimal transient performance even under various nominal operating conditions. With the TLBO method, the step response of the AVR system can be improved.

Design optimisation of PID controller in automatic voltage regulator system using teaching-learning based optimisation algorithm

It is becoming increasingly difficult to ignore the role of the optimal design of the proportional-integral-derivative (PID) controller in achieving a satisfactory response in the automatic voltage regulator (AVR) system. The main aim of this paper is to determine the optimal gains of a PID controller in the AVR system using teaching-learning based optimisation (TLBO) algorithm. Linearly decreasing inertia particle swarm optimisation (LDIPSO) is also employed for comparison purposes. The simulation results are provided to compare the effectiveness of these two different algorithms. MATLAB toolboxes are employed in this paper. Simulation results show that the TLBO algorithm has a considerable potential when compared to one of the best-known heuristic algorithms for optimisation problems. It proves to be more robust than PSO in performing optimal transient performance even under various nominal operating conditions. With the TLBO method, the step response of the AVR system can be improved.

Optimal transient performance under output set‐point reset

SummaryThe purpose of this paper is to propose a new method for the optimization of the output transition in the case of set‐point reset for LTI, non‐minimum phase, possibly non‐hyperbolic plants. Assuming that the plant is stabilized by a proper feedback controller, the problem consists in finding a feedforward linear filter yielding a suitable reference trajectory for the closed‐loop system. The approach situates in the framework of model pseudo‐inversion because the external reference trajectory is computed starting from some desired features of the transient output between the two set points. A significant aspect of the new method is that the transition trajectory is not ‘ad hoc’ exactly prespecified by the designer. Rather, it is implicitly defined by the procedure for the minimization of a suitable multi‐objective quadratic cost functional. As no pre‐actuation is required, the method can be practically implemented on line and also works for the critical class of non‐hyperbolic systems. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Quasi oppositional harmony search algorithm based controller tuning for load frequency control of multi-source multi-area power system

Abstract This paper deals with the load frequency control (LFC) study of single-area and interconnected two-area power system having diversified power sources. The two areas considered in the present study are identical. Each area is having thermal, hydro and gas based power plants. Split-shaft model of gas turbine is used in the present work as one of the diversified generating unit for the purpose of LFC study. Optimal gains of the classical controllers (like integral controller, proportional–integral controller and proportional–integral–derivative (PID) controller, one installed at a time in the studied models) are obtained by using a novel music-inspired metaheuristic harmony search algorithm (HSA) which incorporates quasi opposition based learning technique for memory initialization and also for generation jumping. Single-area power system with diverse power sources is considered and its optimal transient performances are obtained and compared for step load perturbation. The same approach is further extended to two-area interconnected power system consisting of diverse power sources with nominal values of area input parameters. The performance of PID controller is found to be the best one for the studied power system models. It is also revealed that the performance of the interconnected two-area power system with AC–DC tie line is better in comparison to AC tie line.

Neuro-Genetic Adaptive Optimal Controller for DC Motor

Conventional speed controllers of DC motors suffer from being not adaptive, this is because of the nonlinearity in the motor model due to saturation. Structure of DC motor speed controller should vary according to its operating conditions, so that the transient performance is acceptable. In this paper an adaptive and optimal Neuro-Genetic controller is used to control a DC motor speed. GA will be used first to obtain the optimal controller parameter for each load torque and motor reference speed. The data obtained from GA is used to train a neural network; the inputs for the neural network are the load torque and the motor reference speed and the outputs are the controller parameters. This neural network is used on line to adapt the controller parameters according to operating conditions. This controller is tested with a sudden change in the operating conditions and could adapt itself for the conditions and gave an optimal transient performance.

Application of fuzzy subtractive clustering for optimal transient performance of automatic generation control in restructured power system

Nowadays, Automatic Generation Control AGC is a very impressive problem in restructured power system operation for providing electric power with high quality and reliability. In this paper, the three-area multi-units system has chosen for the AGC in restructured power system. Federal energy regulatory commission FERC supports an open market system for price based operation. The theory of DISCO participation matrix is used to simulate the bilateral contracts in the three area multi-units systems. In this paper Fuzzy logic damping controller FLDC for optimal transient performance of AGC has been used. An effective method, namely, Fuzzy Subtractive Clustering is used here, which reduces the number of rules and membership functions of Fuzzy system. This Method provides a mechanism to obtain the reduced rule set covering the whole input/ output space as well as membership functions for each input variable. Finally the results have been compared.

Application of Fuzzy Subtractive Clustering for Optimal Transient Performance of Automatic Generation Control

Automatic Generation Control (AGC) is a very imperative problem in power system operation for providing electric power with high quality and reliability. In this paper, the three-area multi-units AGC is studied. For optimal transient performance of AGC, fuzzy logic damping controller has been used. An efficient approach, namely fuzzy subtractive clustering is used here, which minimizes the number of rules and membership functions of the fuzzy system. This technique provides a mechanism to obtain the reduced rule set covering the whole input/output space as well as membership functions for each input variable. In this paper, a fuzzy subtractive clustering approach is shown to reduce 5, 5, 5 rules to 3, 2, 2 rules, respectively. Finally, the results have been compared.

Improving transient performance in computationally simple gyro-corrected satellite attitude determination

This article extends a previously presented Kalman-like filter for fusing gyro measurements with attitude measurements obtained from external sensors such as star-trackers, magnetometers, and sun-sensors. The simplicity of this approach is useful for applications such as micro/nano-satellites where computational power is limited. The previously presented filter uses constant filter gains. It was shown that by appropriately choosing the constant gains, near- optimal steady-state performance is obtained. A drawback of using constant gains is that optimal transient filter performance is lost, meaning that convergence is slower. In this article, a computationally simple analytical approximation to the transient part of the Kalman filter gain is derived, allowing the transient performance to be recovered. The transient approximation of the gain is then applied for a predetermined fixed period of time, after which the gain is switched to the previously presented constant steady-state Kalman gain. A simple expression for a suitable time to switch from transient to steady-state filter operation is derived. Simulation results demonstrate the efficacy of this approach.

Coordinated control of TCPS and SMES for frequency regulation of interconnected restructured power systems with dynamic participation from DFIG based wind farm

Among the several wind generation technologies, variable-speed wind turbines utilizing doubly fed induction generators (DFIG) are gaining momentum in the power industry. Increased penetration of these wind turbine generators displaces conventional synchronous generators which results in erosion of system frequency. With this assertion, the paper analyzes the dynamic participation of DFIG for frequency control of an interconnected two-area power system in restructured competitive electricity market. Frequency control support function responding proportionally to frequency deviation is proposed to take out the kinetic energy of wind turbine for improving the frequency response of the system. Impacts of varying wind penetration in the system and varying active power support from DFIG on frequency control have been investigated. The presence of thyristor controlled phase shifter (TCPS) in series with the tie-line and Superconducting Magnetic Energy Storage (SMES) at the terminal of one area in conjunction with dynamic active power support from DFIG results in optimal transient performance for PoolCo transactions. Integral gains of AGC loop and parameters of TCPS and SMES are optimized through craziness-based particle swarm optimization (CRPSO) in order to have optimal transient responses of area frequencies, tie-line power deviation and DFIG parameters.