Improvement Of Transient Response Research Articles

Application-Specific Instruction-Set Processor for Control of Multi-Rail DC-DC Converter Systems

Conventional digital signal processor (DSP) based digital controllers are not specifically optimized for multi-rail DC-DC converter applications. A new application-specific instruction-set processor (ASIP) that overcomes the shortcomings of existing controllers has thus been designed, implemented, and evaluated. The proposed dual multiply-accumulate (MAC) architecture has been implemented using a field programmable gate array and verified in a closed-loop power converter system. The benefits of the proposed ASIP are illustrated through a comparison with a conventional single MAC processor architecture. Experimental results demonstrate improved output voltage transient response compared with existing DSP-based controllers when controlling multiple DC-DC converters. In the case of multiple converters that have a non-integer switching frequency ratio more significant improvements in transient response are obtained due to the processor's interrupt controller.

An improved efficiency of fuzzy sliding mode control of permanent magnet synchronous motor for wind turbine generator pumping system

This paper presents an analysis by which the dynamic performances of a permanent magnet synchronous motor (PMSM) motor is controlled through a hysteresis current loop and an outer speed loop with different controllers. The dynamics of the wind turbine pumping drive system with (PI) and a fuzzy sliding mode (FSM) speed controllers are presented. In order to optimize the overall system efficiency, a maximum power point tracker is also used. Simulation is carried out by formatting the mathematical model for wind turbine generator, motor and pump load. The results for such complicated and nonlinear system, with fuzzy sliding mode speed controller show improvement in transient response of the PMSM drive over conventional PI. The effectiveness of the FSM controller is also demonstrated.

Adaptive estimator-based dynamic sliding mode control for the water level of nuclear steam generators

Steam Generator (SG) is a crucial component of nuclear power plant. The proper water level control of a nuclear steam generator is of great importance in order to secure the sufficient cooling source of the nuclear reactor and to prevent damage of turbine blades. The water level control problem of steam generators has been a main cause of unexpected shutdowns of nuclear power plants which must be considered for plant safety and availability. The control problem is challenging, especially at low power levels due to shrink and swell phenomena and flow measurement errors. Moreover, the dynamics of steam generator vary as the power level changes. Therefore, it is necessary to improve the water level control system of SG. In this paper, an adaptive estimator-based dynamic sliding mode control method is developed for the level control problem. The proposed method exhibits the desired dynamic properties during the entire output tracking process independent of perturbations. Simulation results are presented to demonstrate the effectiveness of the proposed controller in terms of performance, robustness and stability. Simulation results confirm the improvement in transient response obtained by using the proposed controller.

Optimal Reset Law Design and Its Application to Transient Response Improvement of HDD Systems

This brief investigates optimal reset law design of reset control systems with fixed reset time instants. First, closed-loop reset control systems are changed to discrete-time linear control systems with reset values as control inputs. Then the optimal reset law design problems are transferred to linear quadratic regulation problems and the optimal reset laws are then obtained by solving algebraic Riccati equations. As an application, the proposed technique is applied to track-seeking control of a kind of hard disk drive systems. Simulations show that the transient response is improved significantly. Especially, the proposed long-span seeking reset control is almost bang-bang, but the design process is much simpler.

Electrical coupling suppression and transient response improvement for a microgyroscope using ascending frequency drive with a 2-DOF PID controller

In this paper, we demonstrate a novel control strategy for the drive mode of a microgyroscope using ascending frequency drive (AFD) with an AGC-2DOF PID controller, which drives a resonator with a modulation signal not at the resonant frequency and senses the vibration signal at the resonant frequency, thus realizing the isolation between the actual mechanical response and electrical coupling signal. This approach holds the following three advantages: (1) it employs the AFD signal instead of the resonant frequency drive signal to excite the gyroscope in the drive direction, suppressing the electrical coupling from the drive electrode to the sense electrode; (2) it can reduce the noise at low frequency and resonant frequency by shifting flicker noise to the high-frequency part; (3) it can effectively improve the performance of the transient response of the closed-loop control with a 2-DOF (degree of freedom) PID controller compared with the conventional 1-DOF PID. The stability condition of the whole loop is investigated by utilizing the averaging and linearization method. The control approach is applied to drive a lateral tuning fork microgyroscope. Test results show good agreement with the theoretical and simulation results. The non-ideal electrical antiresonance peak is removed and the resonant peak height increases by approximately 10 dB over a 400 Hz span with a flicker noise reduction of 30 dB within 100 Hz using AFD. The percent overshoot is reduced from 36.2% (1DOF PID) to 8.95% (2DOF PID, about 75.3% overshoot suppression) with 15.3% improvement in setting time.

An improved efficiency of fuzzy logic control of PMBLDC for PV pumping system

This paper presents an analysis by which the dynamic performances of a permanent magnet brushless DC (PMBLDC) motor is controlled through a hysteresis current loop and an outer speed loop with different controllers. The dynamics of the photovoltaic pumping drive system with (PI) and a fuzzy logic (FL) speed controllers are presented. In order to optimize the overall system efficiency, a maximum power point tracker is also used. Simulation is carried out by formatting the mathematical model for photovoltaic source, MPPT, motor and pump load. The results for such complicated and nonlinear system, with FL speed controller show improvement in transient response of PMBLDC drive over conventional PI. The effectiveness of the FL controller is also demonstrated.

Design and implementation of LQG\LTR controller for a magnetic telemanipulation system-performance evaluation and energy saving

This paper deals with designing a telemanipulation system (TMS) for microrobotics applications. The TMS uses magnetic levitation technology for the three-dimensional (3-D) manipulation of a microrobot. The TMS is made up of two separate components: a magnetic drive unit and a microrobot. The magnetic drive unit is developed to generate the magnetic field for propelling the microrobot in an enclosed environment. The drive unit consists of electromagnets, a disc pole-piece for connecting the magnetic poles, and a yoke. To handle the 3-D high precision motion control of the microrobot, experimental magnetic field measurements coupled with numerical analysis were done to identify the dynamic model of levitation. This approach leads to the design of a linear quadratic gaussian (LQG) control system, based on the derived state-space model. Based on the PID controller performance, the LQG controller provides considerable improvement in transient response and cross coupling errors. The 3-D motion control capability of the LQG control method is verified experimentally, and it is demonstrated that the microrobot can be operated in the TMS workspace, vertical range of 30 mm and the horizontal range of $$32\times 32\,{\text{mm}}^2$$, with RMS error on the order of $$10\,\upmu {\text{m}}$$ in the vertical and $$2.2\,\upmu {\text{m}}$$ in the horizontal direction. In the vertical motion, the cross coupling error of the LQG controller is nine times smaller than that of the PID controller. A pre-magnetized pole-piece is proposed to compensate for gravity effect and reduces the system’s energy consumption. This pole-piece provides 66% energy saving for the system’s workspace operations.

A Low-Power Fast-Transient 90-nm Low-Dropout Regulator With Multiple Small-Gain Stages

A power-efficient 90-nm low-dropout regulator (LDO) with multiple small-gain stages is proposed in this paper. The proposed channel-resistance-insensitive small-gain stages provide loop gain enhancements without introducing low-frequency poles before the unity-gain frequency (UGF). As a result, both the loop gain and bandwidth of the LDO are improved, so that the accuracy and response speed of voltage regulation are significantly enhanced. As no on-chip compensation capacitor is required, the active chip area of the LDO is only 72.5 μm × 37.8 μm. Experimental results show that the LDO is capable of providing an output of 0.9 V with maximum output current of 50 mA from a 1-V supply. The LDO has a quiescent current of 9.3 μA, and has significantly improvement in line and load transient responses as well as performance in power-supply rejection ratio (PSRR).

Transient Response Improvement of Microgrids Exploiting the Inertia of a Doubly-Fed Induction Generator (DFIG)

Storage devices are introduced in microgrids in order to secure their power quality, power regularity and offer ancillary services in a transient period. In the transition period of a low voltage microgrid, from the connected mode of operation to the islanded mode of operation, the power unbalance can be partly covered by the inertia energy of the existing power sources. This paper proposes fuzzy local controllers exploiting the inertia of a Wind Turbine (WT) with a Doubly Fed Induction Generator (DFIG), if such a machine exists in the microgrid, in order to decrease the necessary storage devices and the drawbacks that arise. The proposed controllers are based in fuzzy logic due to the non linear and stochastic behavior of the system. Two cases are studied and compared during the transient period where the microgrid architecture and the DFIG controller differ. In the first case, the understudy microgrid includes a hybrid fuel cell system (FCS)-battery system and a WT with a DFIGURE. The DFIG local controller in this case is also based in fuzzy logic and follows the classical optimum power absorption scenario for the WT. The transition of the microgrid from the connected mode of operation to the islanded mode is evaluated and, especially, the battery contribution is estimated. In the second case, the battery is eliminated. The fuzzy controller of the DFIG during the transition provides primary frequency control and local bus voltage support exploiting the WT inertia. The response of the system is estimated in both cases using MATLAB/Simulink software package.

Hybrid bacterial foraging and particle swarm optimisation for fuzzy precompensated control of flexible manipulator

This paper presents hybrid approach combining the social foraging behaviour of Escherichia coli bacteria and particle swarm optimisation for optimising hybrid fuzzy precompensated proportional-derivative (PD) controller in trajectory control of two-link rigid-flexible manipulator. Numerical simulation using the dynamic model of the two-link rigid-flexible manipulator shows the effectiveness of the approach in trajectory tracking problems. The use of fuzzy precompensation has superior performance in terms of improvement in transient and steady state response, robustness to variations in loading conditions and ease to use in practice. Comparative evaluation with respect to genetic algorithm, particle swarm and bacterial foraging-based optimisation is presented to validate the controller design. The proposed algorithm performs local search through the chemotactic movement operation of bacterial foraging whereas the global search over the entire search space is accomplished by a particle swarm operator and so satisfactory tracking precision could be achieved using the approach.

Transient response improvement of feedback control systems using hybrid reference control

By means of the internal model principle, an approach to improve the performance of a stabilised closed-loop continuous time linear system based on manipulation of the reference signal is developed. A change in the reference signal is equivalent to implementing an instantaneous change via the choice of a decision vector in the state of the reference signal model, and the analysis of the proposed approach called hybrid reference control (HRC) system is then shown to be equivalent to the analysis of a linear impulsive dynamical system. Conditions for asymptotic stability and convergence of the output tracking error for a HRC system are expressed in term of conditions on the decision vectors. Conditions are then derived which guarantee that the HRC system leads to an improved transient performance compared to a conventional closed-loop control system. In particular, it is shown how decision vectors are chosen so that a HRC system results in a deadbeat response.

A Substractive Clustering Based Fuzzy Hybrid Reference Control Design for Transient Response Improvement of PID Controller

The well known PID controller has inherent limitations in fulfilling simultaneously the conflicting control design objectives. Parameters of the tuned PID controller should trade off the requirement of tracking set-point performances, disturbance rejection and stability robustness. Combination of hybrid reference control (HRC) with PID controller results in the transient response performances can be independently achieved without deteriorating the disturbance rejection properties and the stability robustness requirement. This paper proposes a fuzzy based HRC where the membership functions of the fuzzy logic system are obtained by using a substractive clustering technique. The proposed method guarantees the transient response performances satisfaction while preserving the stability robustness of the closed loop system controlled by the PID controller with effective and systematic procedures in designing the fuzzy hybrid reference control system.

An autonomous controller for improved dynamic performance of parallel-connected, single-phase inverters

A new control technique is presented for the parallel connection of distributed generation inverters. The proposed control technique is based on a modification of the power angle droop control method, and uses only locally measured feedback signals. An improvement in transient response is achieved because the real and imaginary components of the output current are used when deriving the power angle droop controller. The method achieves good active and reactive power sharing and minimises circulating current between parallel connected units. Improved transient response is obtained whilst maintaining power sharing precision or output voltage and frequency accuracy. Simulation and experimental results validate that performance is better than that attained with conventional droop-based approaches.

An Active-Frequency Compensation Scheme for CMOS Low-Dropout Regulators With Transient-Response Improvement

An active-frequency compensation circuit for low- dropout regulators (LDOs) is presented. Compared with the conventional compensation scheme, the proposed circuit can greatly boost the effective current multiplication factor by at least one order of magnitude without increasing any power consumption. Hence, the proposed circuit can generate an internal lower frequency zero and push parasitic poles toward extremely high frequency such that the loop bandwidth can be extended drastically. The required on-chip capacitance is reduced to 0.4 pF, comparing to 5 pF in the conventional compensation scheme. The slew rate at the gate drive of the LDO is also improved by the proposed error amplifier. Implemented in a 0.35 mum 2P4M CMOS process, the LDO with the proposed active-frequency compensation circuit consumes 27 muA ground current at 150-mA maximum output current with a dropout voltage of 200 mV. Experimental results show that the proposed LDO structure has achieved only 10% settling time of the conventional compensation scheme.

Autonomous controller for improved dynamic performance of AC grid, parallel-connected, single-phase inverters

A new control technique is presented for the AC grid connection of distributed generation and parallel-connected inverters. The proposed control technique is based on a modification of the power angle droop control method and uses only locally measured feedback signals. An improvement in transient response, including large step transients, is achieved since the coupling filter parameters are taken into consideration when deriving the power angle of a droop controller. Unlike conventional techniques, the proposed technique is stable and minimises the active and reactive power swing for large load changes. The method achieves good active and reactive power sharing and minimises circulating current between parallel connected units and the grid connection, for both linear and nonlinear loads. Improved transient response is obtained while maintaining power-sharing precision, or output voltage and frequency accuracy. Simulation and experimental results validate that performance is better than that attained with conventional droop-based approaches.

Characteristic Analysis of a Micro DC-DC Converter for Portable Electronic Devices and an Improvement of Transient Response Characteristic

This paper describes the characteristic analysis of a micro DC-DC converter which integrates inductor, controller and switching devices, and the improvement of the transient response characteristic. The steady-state operation and the efficiency characteristics of the micro DC-DC converter are presented as experimental data. The static characteristics are theoretically analyzed with consideration of the DC current characteristics of the inductor. The load transient response characteristics of the micro DC-DC converter are also analyzed experimentally and theoretically. In addition, the factors responsible for the overshoot and undershoot of the output voltage when the load changes are discussed. Finally, a clamp circuit for reducing the overshoot and undershoot of the output voltage when the load changes is proposed. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(3): 56–64, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21081

A High Slew-Rate Push–Pull Output Amplifier for Low-Quiescent Current Low-Dropout Regulators With Transient-Response Improvement

A high slew-rate amplifier with push-pull output driving capability is proposed to enable an ultra-low quiescent current (Iq ~ 1muA) low-dropout (LDO) regulator with improved transient responses. The proposed amplifier eliminates the tradeoff between small Iq and large slew-rate that is imposed by the tail-current in conventional amplifier design. Push-pull output stage is introduced to enhance the output driving ability. Small dropout voltage (Vbo) with large-size pass transistor and ultra-low Iq can thus be used to minimize power loss of LDO regulator without transient-response degradation. The proposed amplifier helps to improve stability of LDO regulators without using any on-chip and off-chip compensation capacitors. This is beneficial to chip-level power management requiring high-area efficiency. An LDO regulator with the proposed amplifier has been implemented in a 0.18- mum standard CMOS process and occupies 0.09 mm2. The LDO regulator can deliver 50-mA load current at 1-V input and ~ 100-mV VDO . It only consumes 1.2 muA Iq and is able to recover within ~ 4 mus even under the worst case scenario.

Real-Time Analysis of the Transient Response Improvement of Fixed-Speed Wind Farms by Using a Reduced-Scale STATCOM Prototype

As the total number of installed wind farms is far from being negligible, an upgrading of their technology is essential to fulfil new interconnection requirements. Power electronics are considered to be a key technology to accomplish this task. In this paper the use of a STATCOM for the improvement of the ride-through capability of fixed-speed wind farms is analyzed. Critical aspects like STATCOM rating and control are analyzed. A modified STATCOM controller is proposed, based on the series combination of a power factor control loop and a voltage regulation loop, which permits an optimized behavior of the wind farm both in normal and fault conditions. The contribution of the STATCOM is analyzed by means of Hybrid real-time tests (with a reduced-scale physical prototype) and offline (full scale) simulations in PSCAD/EMTDC. The study highlights the great contribution of STATCOMs to the transient behavior of fixed-speed wind farms and the importance of an appropriate control strategy choice on the performance and rating of the device

Investigation and Improvement of Transient Response of DVR at Medium Voltage Level

An area of interest for dynamic voltage restorer (DVR) research is the damping of transient oscillations initiated at the start and at the recovery instant from a voltage sag. Nonlinear loads, with harmonic currents close to the DVR filter resonance frequency, can also excite the resonance oscillations. To compensate voltage sags and dampen high-frequency oscillations simultaneously, an investigation of the transient response of DVR is first carried out. Possible control schemes and their effects on the oscillation attenuation are also studied. Such studied control schemes include the commonly used single voltage loop control, voltage feedback plus reference feedforward control, and double-loop control with an outer voltage loop and an inner current loop. Subsequently, an effective and simple resonance damping method is proposed by employing a closed-loop control with an embedded two-step Posicast controller. The proposed control methods have been extensively tested on a 10-kV DVR system. It is shown that the proposed damping methods improve both the transient and steady-state performance of the DVR.

ARTIFICIAL INTELLIGENCE AND GRAPH THEORY TOOLS FOR DESCRIBING SWITCHED LINEAR CONTROL SYSTEMS

This paper develops a representation of multi-model based controllers using artificial intelligence techniques. These techniques will be graph theory, neural networks, genetic algorithms, and fuzzy logic. Thus, graph theory is used to describe in a formal and concise way the switching mechanism between the various plant parameterizations of the switched system. Moreover, the interpretation of multi-model controllers in an artificial intelligence frame will allow the application of each specific technique to the design of improved multi-model based controllers. The obtained artificial intelligence-based multi-model controllers are compared with classic single model-based ones. It is shown through simulation examples that a transient response improvement can be achieved by using multi-estimation based techniques. Furthermore, a method for synthesizing multi-model-based neural network controllers from already designed single model-based ones is presented, extending the applicability of this kind of technique to a more general type of controller. Also, some applications of genetic algorithms and fuzzy logic to multi-model controller design are proposed. In particular, the mutation operation from genetic algorithms inspires a robustness test, which consists of a random modification of the estimates which is used to select the one leading to the better identification performance towards parameterizing online the adaptive controller. Such a test is useful for plants operating in a noisy environment. The proposed robustness test improves the selection of the plant model used to parameterize the adaptive controller in comparison to classic multi-model schemes where the controller parameterization choice is basically taken based on the identification accuracy of each model. Moreover, the fuzzy logic approach suggests new ideas to the design of multi-estimation structures, which can be applied to a broad variety of adaptive controllers such as robotic manipulator controller design.