Deadband Effect Research Articles

Command filter-based adaptive neural tracking control of nonlinear systems with multiple actuator constraints and disturbances

In this paper, the adaptive practical finite-time tracking control problem for a class of strictly feedback nonlinear systems with multiple actuator constraints is investigated using backstepping techniques and practical finite-time stability theory. The effects of deadband and saturated nonlinear constraints on the controller design of nonlinear systems are addressed by the equivalent transformation method. The problem of complexity explosion due to the derivatives of virtual control signals is solved by using the virtual control signals as inputs to the command filters and using the outputs of the command filters to perform the corresponding control tasks. An adaptive neural network tracking backstepping control strategy based on the command filter technique and the backstepping design algorithm is proposed by approximating an unknown nonlinear function using a neural network. The control strategy ensures the boundedness of all variables in the closed-loop system, and the output tracking error fluctuates in a small region near the origin. Finally, simulations verify the effectiveness of the control strategy designed in this paper.

A regular sampling method based on the immediate mode for improving the stability of inverters

The shadow mode-based regular sampling methods are usually used in the digital control of power inverters, which introduce a control delay of one and a half sampling periods. The control delay affects the closed loop bandwidth and the stability of dc–ac inverters. Recently, regular sampling methods based on the immediate mode is emerging and helpful for reducing the digital control delay. When employing the immediate mode, the induced vertical crossings may arouse the duty-cycle loss and dead-band effect during the modulation process, which deteriorate the normal operation of the inverters. Although the duty-cycle loss can be avoided by forcing the PWM signal to flip at the occurrence of vertical crossings, the introduced dead bands still exist. Thus, this paper investigates the phenomenon of vertical crossings and proposes a control algorithm composed of predicting the occurrence of vertical crossings and compensating the dead-band effect for regular sampling methods based on the immediate mode. Finally, experimental results on a single-phase dc–ac inverter prototype are provided to compare the efficacy of different approaches.

A Universal Multicarrier Multisampling Method for Digitally Controlled Inverters

For reducing the control delays introduced by the digital control of dc/ac converters, multisampling technology applying high sampling frequency of exact multiples of the switching frequency becomes attractive. In this way, higher control bandwidth and stability margin are achievable. However, multiupdate (>2) of the modulation signal within one switching cycle is not usually allowed on the digital signal processors. Besides, multiupdate within one switching cycle leads to an abnormal phenomenon referred to as vertical crossing when the modulation signal intersects the carrier signal vertically. The vertical crossing further causes the deadband effect of the pulsewidth-modulation signal and distortion of the output waveform. The abovementioned phenomenon greatly restricts the application of multisampling technology. In order to break the aforementioned barriers, a novel multicarrier-based multisampling method by dividing the triangular carrier signal into <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> equal sawtooth segments is proposed in this article. Moreover, the problem of vertical crossings and the resulting deadband effect in the multiupdate mode is solved. Simulation and experimental results on a single-phase dc–ac inverter are provided to validate the effectiveness of the proposed approach.

Improvement of Automatic Generation Control Behavior of Two Interconnected Areas Using SMES and TCSC

In this paper, an attempt has been made to enhance the dynamic behaviour of Automatic Generation Control (AGC) of two areas two units using both Thyristor Controlled Series Compensator (TCSC) placed in the tie-line and Superconducting Magnetic Energy Storage (SMES) units are considered in both areas. For more realistic study, the effects of Governor Dead Band (GDB) and Generation Rate Constraints (GRCs) are taken into account for both areas. However, to conduct the system to better dynamic responses, we have implemented a PI-PD cascade controller. After that, a well-known and powerful optimisation algorithm named Firefly Algorithm (FA) is employed by evaluating the Integral of the Squared Error (ISE). From the obtained results, the implemented methods prove its efficiency from different view of points such as: minimisation of Overshoot and Undershoot Peaks (PO), (PU) and Settling Time (ST).

Effect of Dead Band and Transient Actions on CTPS Modulation for DAB DC–DC Converter and Solutions

As the key part of the electric vehicle charger with the V2G functions, the isolated dual-active-bridge (DAB) dc-dc converter should possess good current characteristics. The cooperative triple-phase shift (CTPS) modulation for the DAB converter realizes the best inductor current performance. However, the dead band and transient actions deteriorate the actual performance of the CTPS. In this article, the effect is analyzed for the first time, and the analysis results indicate that both the dead band and transient actions cause the dc-bias inductor current and the dc-side flow back currents. The corresponding solutions to eliminate these effects are proposed accordingly. First, a phase shift compensation related to the dead time is added to the ideal phase shifts from CTPS to eliminate the effect of the dead band. Second, the relationship between the three phase shifts is recalculated considering the old values of the phase shifts to eliminate the transient dc-bias currents and flow back currents. The proposed solutions are validated in detail in an experimental way.

Deadband Effect and Accurate ZVS Boundaries of GaN-Based Dual-Active-Bridge Converters With Multiple-Phase-Shift Control

Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) are promising for the next-generation power switching applications due to their low on-resistance, high-frequency operation, and small gate capacitances, which are essential for the power density and efficiency improvement. However, with the increase of the switching frequency, the deadband effect will become a challenging issue for the high-efficiency converter design over a wide operation range. In this article, a comprehensive theoretical analysis and experimental verification of the deadband effect in the GaN-based dual-active-bridge (DAB) converters with multiple-phase-shift (MPS) control is presented. First, resonant transitions for various switching conditions with different initial currents by using MPS controls are discussed, and the effect of the stray capacitance of GaN HEMTs is analyzed. On this basis, the accurate boundaries among zero-voltage switching (ZVS), partial ZVS, and hard switching with MPS control can be obtained. A deadband compensation strategy is proposed by considering different switching conditions. Finally, a DAB prototype based on GaN HEMTs was built, and main experimental results were provided to verify the effectiveness of the proposed resonant transition analysis, ZVS boundaries, and the deadband compensation strategy.

Agent Based Modeling in Energy Systems: Parametrization of Coupling Points

Future multimodal energy systems (MES) including heat, gas and electricity sectors will be equipped with control systems, which have some degree of autonomy, and are adaptive to their environment. Smart control systems are able to communicate with other systems and other autonomous controllers. The resulting systems can be analyzed as a complex adaptive system (CAS), which has been successfully investigated using agent based modeling (ABM) in the past. In this study, the operational behavior of a MES using different agent parametrizations for coupling points is investigated. These properties can be categorized as fast-acting agents and slow-acting as well agents with and without dead-band and saturation. The result of every scenario points out the temporal evolution of pressure in gas, temperature in heat and voltage in electricity sectors. The bottom-up perspective allocates agents’ parametrizations to the whole system behavior. The study shows the effect of dead-band, saturation and the gain of coupling points controller on the MES. In addition, the role of observers in analyzing systems in CAS paradigm is discussed. The results pave the way for setting up proper agents’ parameters and designing proper observers.

Improved Modulation Strategy for Single-Phase Isolated Quasi-Single-Stage AC–DC Converter to Improve Current Characteristics

In this article, an improved triple-phase-shift (ITPS) modulation for the single-phase isolated quasi-single-stage ac–dc converter is proposed to realize the current decouple between the adjacent switching periods and to reduce the grid current distortion. Moreover, the dead band effect on the proposed ITPS is analyzed for the first time. It reveals that the dead band causes not only the current couple and accordingly the grid current distortion but also the current amplitude loss. A two-step phase-shift compensation scheme is proposed based on the analysis result to solve the problems caused by the dead band. All of the theoretical analysis, the proposed ITPS modulation, and the dead band compensation scheme are validated in detail in the experimental way.

Automatic Generation Control Incorporating Electric Vehicles

Electrical vehicles (EVs) enjoying the new technology known as vehicle-to-grid have presented new opportunities to control and planning of power grids. Bidirectional connection capability of converters in EVs’ structure makes them a secure backup for frequency support. This paper applies EVs as one of the foremost controllable loads along with other conventional generation units for frequency control after disturbances in a multi-area power system. Application of tilt-integral-derivative (TID) controller for EVs has been addressed for the first time in this paper. In this regard, artificial bee colony optimization algorithm is employed for optimal tuning parameters of TID controllers in EV and automatic generation control structures. In order to achieve accurate and realistic results, physical limitations of generation rate constraint, non-linearity, and governor dead-band effect are included in the analysis. Eventually, three scenarios including step and random load changes, and sensitivity analysis are selected to illustrate the efficiency of the proposed coordinated control in terms of settling time, peak time, peak overshoot, and the integral of time multiplied squared error performance index in frequency and tie-line power deviations. The results are compared with particle swarm optimization and genetic algorithm based TID controllers.

An intelligent coordinator design for GCSC and AGC in a two-area hybrid power system

This study addresses the design procedure of an optimized fuzzy fine-tuning (OFFT) approach as an intelligent coordinator for gate controlled series capacitors (GCSC) and automatic generation control (AGC) in hybrid multi-area power system. To do so, a detailed mathematical formulation for the participation of GCSC in tie-line power flow exchange is presented. The proposed OFFT approach is intended for valid adjustment of proportional–integral controller gains in GCSC structure and integral gain of secondary control loop in the AGC structure. Unlike the conventional classic controllers with constant gains that are generally designed for fixed operating conditions, the outlined approach demonstrates robust performance in load disturbances with adapting the gains of classic controllers. The parameters are adjusted in an online manner via the fuzzy logic method in which the sine cosine algorithm subjoined to optimize the fuzzy logic. To prove the scalability of the proposed approach, the design has also been implemented on a hybrid interconnected two-area power system with nonlinearity effect of governor dead band and generation rate constraint. Success of the proposed OFFT approach is established in three scenarios by comparing the dynamic performance of concerned power system with several optimization algorithms including artificial bee colony algorithm, genetic algorithm, improved particle swarm optimization algorithm, ant colony optimization algorithm and sine cosine algorithm.

Estimation of Inherent Governor Dead-Band and Regulation Using Unscented Kalman Filter

The inclusion of the governor droop and dead-band in dynamic models helps to reproduce the measured frequency response accurately and is a key aspect of model validation. Often, accurate and detailed turbine-governor information are not available for various units in an area control centre. The uncertainty in the droop also arise from the nonlinearity due to the governor valves. The droop and dead-band are required to tune the secondary frequency bias factors, and to determine the primary frequency reserve. Earlier research on droop estimation did not adequately take into account the effect of dead-band and other nonlinearities. In this paper, unscented Kalman filter is used in conjunction with continuously available measurements to estimate the governor droop and the dead-band width. The effectiveness of the approach is demonstrated through simulations.

Modified group search optimisation‐based comparative performance evaluation of thyristor controlled series capacitor‐based fractional order damping controllers to improve load frequency control performance in restructured environment

This study compares fractional order phase lead-lag controller, fractional order proportional-integral-derivative (FOPID), and tilt-integral-derivative controllers as thyristor controlled series capacitor (TCSC)-based damping controller to improve load frequency control (LFC) performance in a restructured power system. To prepare an efficient ancillary service, a precise formulation for participation of TCSC in tie-line power flow exchange is presented which is compared with the earlier Taylor-based approximated model. The controller parameters are adjusted by employing different evolutionary algorithms. To obtain realistic results under a competitive environment, a diverse-GENCOs multi-DISCOs power system with the generation rate constraint and governor dead-band effects, communication time delay, bilateral contracts, and pool-co transactions is taken into account. Non-linear time-domain simulations demonstrate that the FOPID-based TCSC damping controller in coordination with an integral-type simple LFC can most effectively suppress the area frequency and tie-line power oscillations. Further investigations are performed for uncontracted higher order step and random load demands treated as contract violation scenarios to confirm the superiority of the proposed fractional order controllers-based TCSC–LFC over the Taylor-based TCSC–LFC. The sensitivity analysis is done for a wide range of loading condition and system parameters to compare the robustness of the considered controllers.

Minimum frequency estimation of power system considering governor deadbands

The extensive existence of governor deadband has a significant influence on the minimum frequency of power system after a disturbance. However, the strong nonlinearity of deadband makes it difficult to quantify its impact on the frequency response. For this end, the backlash non-linearity is adopted to represent for the governor with deadband. The non-linear characteristics of governor with deadband are thus well approximated. The describing function method is applied to linearise the backlash non-linearity. Then a first-order model of governor system is derived to consider the deadband effect quantitatively. Minimum frequency estimation algorithm is proposed based on the first-order model. The proposed algorithm is effective to reflect the effects of various widths of deadbannd on the minimum value of frequency. Case study is conducted to prove its adequate performance in minimum frequency estimation with a practical power grid in China.

MGSO optimised TID‐based GCSC damping controller in coordination with AGC for diverse‐GENCOs multi‐DISCOs power system with considering GDB and GRC non‐linearity effects

This study presents automatic generation control (AGC) in the presence of a gate controlled series capacitor (GCSC) to provide an effective frequency control ancillary service for a two-area diverse-GENCOs multi-DISCOs power system. First, the contribution of the GCSC in tie-line power exchange is formulated mathematically and then a tilt-integral-derivative (TID)-based damping controller is proposed. The effectiveness of the proposed TID-based GCSC-AGC coordinated controller is compared with just AGC, proportional-integral-derivative-based GCSC-AGC, thyristor controlled series capacitor-AGC, static synchronous series compensator-AGC, and thyristor controlled phase shifter-AGC. A modified group search optimisation (MGSO) algorithm is employed to adjust the considered controllers. Physical limitations of generation rate constraint (GRC) non-linearity and governor dead-band (GDB) effect are taken into account in the evaluations to obtain realistic results. Bilateral contracts and pool-co transactions are considered concurrently for the realisation of a competitive environment. Simulations reveal that the proposed controller outperforms the other controllers in providing better dynamic responses. Additional evaluations are performed under the un-contracted step, sinusoidal and random load demands seen as contract violations to demonstrate the superiority of the proposed controller over other controllers. Sensitivity analyses are performed for different uncertainty scenarios to show the robustness of the proposed control approach.

Photovoltaic Frequency–Watt Curve Design for Frequency Regulation and Fast Contingency Reserves

When renewable energy resources are installed in electricity grids, they typically increase generation variability and displace thermal generator control action and inertia. Grid operators combat these emerging challenges with advanced distributed energy resource (DER) functions to support frequency and provide voltage regulation and protection mechanisms. This paper focuses on providing frequency reserves using autonomous IEC TR 61850-90-7 pointwise frequency–watt (FW) functions that adjust DER active power as a function of measured grid frequency. The importance of incorporating FW functions into a fleet of photovoltaic (PV) systems is demonstrated in simulation. Effects of FW curve design, including curtailment, deadband, and droop, were analyzed against performance metrics using Latin hypercube sampling for 20%, 70%, and 120% PV penetration scenarios on the Hawaiian island of Lanai. Finally, to understand the financial implications of FW functions to utilities, a performance function was defined based on monetary costs attributable to curtailed PV production, load shedding, and generator wear. An optimization wrapper was then created to find the best FW function curve for each penetration level. It was found that in all cases, the utility would save money by implementing appropriate FW functions.

Quasi-oppositional symbiotic organism search algorithm applied to load frequency control

Abstract The present work approaches a relatively new optimization scheme called “quasi-oppositional symbiotic organism search (QOSOS) algorithm”, for the first time, to find an optimal and effective solution for load frequency control (LFC) problem of the power system. The symbiotic organism search (SOS) algorithm works on the effect of symbiotic interaction strategies adopted by an organism to survive and propagate in the ecosystem. To avoid the suboptimal solution and to accelerate the convergence speed, the theory of quasi-oppositional based learning (Q-OBL) is integrated with original SOS and used to solve the LFC problem. To demonstrate the effectiveness of QOSOS algorithm, two-area interconnected power system with nonlinearity effect of governor dead band and generation rate constraint is considered at the first instant, followed by the four-area power system showing the consequence of load perturbation. The structural simplicity, robust performance and acceptability of well-popular proportional-integral-derivative (PID) controller enforce to implement it as a secondary controller for the present analysis. The success of QOSOS algorithm is established by comparing the dynamic performances of concerned power system with those obtained by some recently published algorithms available in the literature. Furthermore, the robustness and sensitivity are analyzed for the concerned power system to judge the efficacy of the proposed QOSOS approach.

Quasi-oppositional differential search algorithm applied to load frequency control

In this article, quasi-oppositional differential search algorithm (QODSA) is proposed for finding an optimal and effective solution for load frequency control (LFC) problem in the power system. Initially, original DSA is employed for fine-tuning of the secondary controller of LFC system and then, quasi-oppositional based learning (Q-OBL) mechanism is integrated into the original DSA to enhance the convergence speed and to find a better solution of LFC problem. To validate the effectiveness of proposed QODSA, four widely used interconnected power system networks are designed and analyzed. The superiority of the proposed method is established by an extensive comparative analysis with other existing evolutionary algorithm’s (EA) using transient analysis method. A critical investigation of simulation results reveals that the proposed QODSA gives simple and better solution compared to original DSA and other reported algorithms. To study the robustness of QODSA, two different random load patterns are projected and results confirm the robustness of the designed controllers. To add some degree of nonlinearity, generation rate constraint and governor dead band effects are considered and their consequence on the system dynamics has been examined. Finally, sensitivity analysis is performed with a wide variation of system parameters.

Effects of dead-band and set-point settings of on/off controllers on the energy consumption and equipment switching frequency of a residential HVAC system

Residential heating, ventilation and air conditioning (HVAC) systems generally employ simple on/off controllers to regulate the temperature of water and air in different subsystems. Selection of set-point of a controlled process and dead-band of controller affects the process regulation, energy consumption and actuator switching frequency. This article presents a calibrated model of a residential HVAC system. Temperature of two zones and buffer tank (BT) is regulated using on/off controllers. Non optimum controller settings result in poor regulation, higher energy consumption and higher equipment wear. The purpose of this article is to find optimum set-point and dead-band settings for on/off controllers in order to improve temperature regulation, reduce energy consumption and decrease equipment wear by reducing the switching frequency of HVAC equipment without scarifying thermal comfort of occupants.

Applying fractional order PID to design TCSC-based damping controller in coordination with automatic generation control of interconnected multi-source power system

In this paper, fractional order proportional-integral-differential (FOPID) controller is employed in the design of thyristor controlled series capacitor (TCSC)-based damping controller in coordination with the secondary integral controller as automatic generation control (AGC) loop. In doing so, the contribution of the TCSC in tie-line power exchange is extracted mathematically for small load disturbance. Adjustable parameters of the proposed FOPID-based TCSC damping controller and the AGC loop are optimized concurrently via an improved particle swarm optimization (IPSO) algorithm which is reinforced by chaotic parameter and crossover operator to obtain a globally optimal solution. The powerful FOMCON toolbox is used along with MATLAB for handling fractional order modeling and control. An interconnected multi-source power system is simulated regarding the physical constraints of generation rate constraint (GRC) nonlinearity and governor dead band (GDB) effect. Simulation results using FOMCON toolbox demonstrate that the proposed FOPID-based TCSC damping controller achieves the greatest dynamic performance under different load perturbation patterns in comparison with phase lead-lag and classical PID-based TCSC damping controllers, all in coordination with the integral AGC. Moreover, sensitivity analyses are performed to show the robustness of the proposed controller under various uncertainty scenarios.

Performance comparison of TCSC with TCPS and SSSC controllers in AGC of realistic interconnected multi-source power system

Abstract The primary goals of employing series flexible ac transmission system (FACTS) in automatic generation control (AGC) studies of interconnected power systems are mitigating area frequency and tie-line power oscillations. This paper compares dynamic performance of thyristor controlled series capacitor (TCSC) as damping controller with thyristor controlled phase shifter (TCPS) and static synchronous series compensator (SSSC) which are series FACTS damping controllers. Commonly used lead-lag controllers are used in structure of damping controllers. The effect of TCSC in tie-line power exchange is modeled mathematically based on the Taylor series expansion for small-signal load disturbance. The performance of the proposed TCSC controller in coordination with integral AGC is compared with cases of TCPS–AGC and SSSC–AGC. An improved particle swarm optimization (IPSO) algorithm and integral of time multiplied squared error (ITSE) performance index are used to design the damping controllers. A two-area power system having generations from reheat thermal, hydro, and gas units in each area is evaluated regarding nonlinearity effects of generation rate constraint (GRC) and governor dead band (GDB). The simulations results in MATLAB/SIMULINK environment show that the proposed TCSC–AGC yields superior performance than others in damping of area frequencies and tie-line oscillations. Furthermore, sensitivity analyses are performed to show greater robustness of TCSC–AGC.