Flexible Control Strategy Research Articles

Techno-economic analysis of flexible heat pump controls

There exists a gap between the flexibility needed within the German energy system and the flexibility being actually provided. Heat pumps can be seen to be the core technology to couple the heating and electricity sectors and thereby provide flexibility to the system. We contribute to the scientific discussion by conducting validated simulations of realistic and easily applicable heat pump control methods that are implemented to provide flexibility and not limited to pilot trials. We assess effects on energy efficiency and economic potentials compared to standard reference control algorithms. The flexible control schemes under investigation can be divided into two categories: time-of-use based controls and spot market price based control. We investigate both control types for current market conditions and for future scenarios of the German electricity market in 2030. In our study, we introduce a validated MODELICA simulation model of a ground source heat pump and market models to evaluate financial consequences. Our results indicate that efficiency losses occur for all investigated control methods. Further, financial gains for heat pump owners could not be achieved with current price structures, only distinct future scenarios with high shares of fluctuating renewables and low electricity demand led to enough price fluctuations to allow for electricity cost savings. Thus, we conclude that (1) heat pump owners need to weigh pros and cons of currently applicable, flexible heat pump controls carefully before their implementation, (2) there exists a need for heat pump manufacturers to further develop controllers that are capable of more advanced control schemes on large-scale, (3) policy makers should establish market mechanisms to ensure that heat pump owners are provided with incentives to use flexible controls, and (4) scientific modelers should not only focus on the development of highly elaborated control methods, but also investigate their transferability to large-scale real-world applications in the near future.

Flexible control of DC interlinked multiple MGs cluster

A cluster with multiple AC or DC microgrids (MGs) based on flexible DC interlinking and distributed energy storage systems is studied in this paper, which has been identified to have the following issues in terms of its primary control scheme: coordinated power control among slack terminals in the MG cluster, seamless operation mode transition for the interlinking converters and the common DC bus voltage control. A novel flexible control scheme that unifies the control of all the MGs only using local measured signals without further communications is proposed in this paper, which aims to improve control stability, and operation reliability and flexibility. Theoretical introduction and analysis are presented to explain the proposed control. The detailed average value model and small-signal model of an MG cluster with two AC MGs and two DC MGs are simulated, respectively, with the proposed control in power systems computer-aided design/electro-magnetic transient design and control to verify the effectiveness in control stability and flexibility enhancement, and the impact of control parameters on the small-signal stability of the considered cluster is analysed through root locus.

Flexible Voltage Control Strategy Considering Distributed Energy Storages for DC Distribution Network

In this paper, a flexible voltage control strategy, which takes good use of the distributed energy storage (DES) units, is proposed to enhance the voltage stability and robustness of dc distribution network. The characteristics of ac/dc interface in network are analyzed, and the virtual inertia and capacitance are given to demonstrate the interactive influence of the ac and the dc systems. The control strategy for DES which is located at the ac microgrid or at the network terminal bus is designed based on the interactive characteristics, enabling the DES to respond to both voltage variation of dc network and frequency change of utility ac grid. A cascading droop control strategy is proposed for DES in dc microgrid to relieve the pressure of voltage deterioration of dc network buses which connect the dc microgrid. The proposed comprehensive flexible control strategy for DESs at different interfaces features independence of communication as well as enhancement of system robustness, and reduces the impact of dc distribution network on utility ac grid. The performance of the proposed control strategy is validated under different operating conditions of the dc distribution network.

Flexible Power Control for Wireless Power Transmission System With Unfixed Receiver Position

To improve the stability of receiving power in the wireless power transmission system with unfixed receiving position, a flexible power control strategy without the measurement in secondary side and the wireless communication between primary and secondary sides is proposed. The circuit model of a multiphase resonant inverter (MPRI) with cascaded intercell transformers (ICTs) is developed. The output voltage control strategy of the MPRI is introduced based on the iterative summation method for trigonometric functions. The circuit model of the system is derived to deduce the expressions for the key parameters. Considering the cascaded ICTs and the inductor–capacitor–capacitor ( LCC ) compensation circuit in the primary side, the design method of the compensation parameters is proposed based on the circuit model of the MPRI. After synthesizing the online monitoring, parameter pre-calculation, prediction of several conditions, and online learning, the flexible power control strategy is put forward for the wireless power transmission system with unfixed receiver position. Without the auxiliary positioning methods, the measurement in the secondary side, or the wireless communication between primary and secondary sides, the recognition of the load access and exit, as well as the power stabilization control after access, are realized. Finally, the theoretical analyses and the control strategy are validated by experiments.

Progressive Image Restoration Based on CP-ABE With Constant-Size Ciphertext and Constant Bilinear Calculation

Sharing photos on an open social platform with one-to-many features increases the leakage risk of information of the shared photos. Ciphertext-policy attribute-based encryption (CP-ABE) is a one-to-many public key cryptosystem, and its access policy can be set by data owners. Therefore, if we share the protected image on the social platform and encrypt the restoration parameters of the shared image with CP-ABE, then only the accessor whose attribute set satisfies the access policy of CP-ABE can decrypt the ciphertext corresponding to his/her attribute level and then restore the image with the corresponding sharpness level. Consequently, image information protection is realized in a one-to-many scenario. However, for the existing CP-ABE, only when further shortening its ciphertext, reducing the number of bilinear pairing calculations during decryption, and ensuring flexible access policies is it beneficial for CP-ABE to be widely used in popular smart terminals that can run social software. Furthermore, existing algorithms for restoring images also have room for improvement in terms of time and space requirements. For this reason, we propose a progressive image restoration strategy based on the improved CP-ABE in this paper. For the improvement of CP-ABE, we design a new encryption scheme to achieve a shorter constant-size ciphertext, construct an auxiliary function to help the independent authority centers generate private keys for users in new ways, design a decryption algorithm with only one bilinear pairing calculation, and provide the update algorithms for attribute revocation. Subsequently, we build a distributed CP-ABE based on our improved CP-ABE, and the correctness and security of the proposed CP-ABE algorithm are also proven. In addition, we follow the tree access policy to support the access policy, including AND, OR, NOT and threshold operations simultaneously, to adapt to the requirement of some user attributes that undergo frequent changes. Moreover, based on the atmospheric scattering model, we adopt three algorithms to restore the protected image in the dehazing mode according to the sharpness parameters. Compared with the existing literature, we provide users with not only a flexible and efficient access control strategy, shorter constant-size ciphertext and fewer bilinear calculations but also multiple algorithms for restoring images. The experimental results for six privilege levels demonstrate the superiority of our algorithms in protecting image information.

Autonomous Base Station Placement for Localization of the GNSS Interference Source

This paper presents the control strategy of autonomous base station placement for localization of the GNSS interference source. The proposed algorithm deals with the optimization of the base station trajectory for target motion analysis based on bearing only tracking problem. The control strategy of the proposed algorithm is designed to maximize a cost function which is generally a functional of the Fisher information matrix. Compared to the optimal control methods, the proposed algorithm is easy to be designed and implemented, and constraints of multiple base stations’ trajectories can be effectively included. In addition, the proposed algorithm also considered target’s dynamics that is both uncertain and random, and there are multiple base stations for observing the target. In order to verify the performance of the proposed algorithm, simulation was performed with dynamic target case in the 2D scenario. It is assumed that the base stations’ networks have non-fully connected topology. According to the simulation results, it was confirmed that the proposed algorithm presents a flexible control strategy of autonomous multiple base stations’ placement for bearing only target tracking system.

A Mathematical Model: A Flexible Manufacturing System, Prone to Error, Making Two Products Each with Stochastic Demand Schedules

Lockout/tagout (LOTO) is practiced in manufacturing facilities to ensure safety during machinery maintenance procedures. In flexible manufacturing systems, human error (HE) is a major source of accidents and process deviations. Special measures are needed to minimize occupational risk and increase operational efficiency. In this article, we study a production planning problem involving a failure-prone production system meeting two types of demand and we discuss the associated decision-making process. The aim is to develop an optimal, robust and flexible control strategy that facilitates the integration of LOTO into corrective maintenance (CM) and ultimately into production. The influence of HE on flexible manufacturing systems (FMS) is viewed in terms of production and maintenance planning. The frequency of machine repair depends largely on HE. The intrinsic costs of shortage, inventory and CM are optimized over an unbounded planning horizon. Analytical formalism is combined with discrete event simulation, as well as design of experiments (DOE) and a genetic algorithm (GAs) to identify the optimal planning of production and CM with mandatory LOTO. An illustration and sensitivity analysis are proposed to express, in quantitative terms, the usefulness and efficiency of the proposed approach.

Production Planning and Control as Routing in Manufacturing Networks

In this paper, we explore the use of network routing for production planning and control in manufacturing of complex industrial products. Such a product is the result of a joint effort of many manufacturing companies; each considered a collection of work centre nodes connected by transportation links forming a company-wide manufacturing network. Each company is, in turn considered a manufacturing node connected to other manufacturers by transportation links forming a distributed manufacturing network that produces the final product. We model the manufacturing network as a distribution network where the incoming and outgoing inventories of products are distinct nodes in addition to the work centre nodes. Production planning and control are done by minimizing the cost of handling all products in all work centre nodes. This formulation provides a scalable and flexible production planning and control scheme adhering to the networked structure of manufacturing of complex products. We apply the model to a company-wide manufacturing network as a first approach. A case study using the model demonstrates production planning using network routing at a manufacturer of ship propulsion engines.

A bilayer interaction strategy for air‐conditioning load aggregators considering market‐based demand response

With considerable portion of air-conditioning load in total power consumption, air-conditioning load aggregators are authorised to participate in power market by aggregating large amounts of air-conditioning load with or without ice storage system. This paper studies on a bilayer interaction strategy for air-conditioning load aggregators considering market-based demand response, on the basis of a hierarchical deregulated day-ahead market architecture. In the upper layer, load aggregators submit their bids to independent system operator (ISO), after evaluating their load regulation potential. With the aim of minimising load dispatch cost, ISO optimises the dispatch schedule and informs each LA of its bid-winning capacity under a pay-as-bid pricing scheme. In the lower layer, air-conditioning load aggregator adopts a flexible control strategy to optimise the control actions in an effort to maximise its own benefits, as well as keeping indoor temperature within the temperature range in the contract and achieving the desired aggregated demand response capacity allocated by ISO in the upper layer. Thermal dynamic characteristics and corresponding power consumption characteristics of air-conditioning load control strategies are analysed. The resulting model is a mixed-integer non-linear optimisation problem. Finally, simulation verifies the feasibility and effectiveness of the proposed strategy.

A Flexible Power Control Strategy for Hybrid AC/DC Zones of Shipboard Power System With Distributed Energy Storages

The use of integrated shipboard power system (SPS) has greatly contributed to the next-generation vessels development. In this sense, how to realize the reasonable power distribution between hybrid zones in SPS is becoming one of the key problems to ensure system robustness and reliability. In this paper, a flexible power control strategy is proposed for the coordinated operation of the hybrid ac/dc zones in SPS. First, the interactive relationship of the ac/dc interface is analyzed, and the virtual inertia and capacitance are defined to reveal the interactive influence of the ac and the dc subgrids, which leads to a new V-f droop principle. Then, the flexible control strategy is designed based on the droop principle as well as the characteristics of the analogous virtual synchronous generator, and the key parameters’ determination are discussed in detail, which can realize a proper assignment of cross-zone supportive power and improve the system dynamic response. In addition, the coordinated control loops are designed with the distributed energy storages and interlinking converters for the implementation of the strategy. Finally, the proposed strategy is validated by the simulation, which shows that the strategy can enhance the power quality and dynamics of the hybrid zones and contribute to the robustness of the whole SPS .

Disturbance Rejection Control Method for Isolated Three-Port Converter with Virtual Damping

The high-power density and capability of three-port converters (TPCs) in generating demanded power synchronously using flexible control strategy make them potential candidates for renewable energy applications to enhance efficiency and power density. The control performance of isolated TPCs can be degraded due to the coupling and interaction of power transmission among different ports, variations of model parameters caused by the changes of the operation point and resonant peak of LC circuit. To address these issues, a linear active disturbance rejection control (LADRC) system is developed in this paper for controlling the utilized TPC. A virtual damping based method is proposed to increase damping ratio of current control subsystem of TPC which is beneficial in further improving dynamic control performance. The simulation and experimental results show that compared to the traditional frequency control strategy, the control performance of isolated TPC can be improved by using the proposed method.

A flexible control strategy for energy and comfort aware HVAC in large buildings

A data driven framework for the energy and comfort management in large buildings with multiple zones and dynamic occupancy patterns is presented in this paper. For such cases, precise heat conduction models derived using the classical thermal physics laws will be cumbersome. The approach uses the historical data to develop a multi-variable model through Structural Equation Modeling (SEM) so as to identify the relative dominance of the direct and indirect effects of thermal coupling among the neighboring zones, occupancy and the external climate variations on the thermal behavior of the building zones. Based on the information gathered from the SEM, we can predict the return temperatures more accurately, which in turn is employed to incorporate a flexible control strategy for the HVAC system. A controller fed with the temperature error and occupancy error, between the predicted and measured values, regulates the supply air fan speed via VFD motor and outside air damper valve openings. This has resulted in the energy savings while maintaining the occupant thermal comfort at the reasonable levels. The framework proposed has been evaluated using real data collected from an HVAC system of a big airport terminal building. The results show that the accuracy of prediction is relatively higher than with other regression techniques; and that the HVAC system is energy efficient and can ensure occupant comfort on real-time basis in large buildings.

Harmonic Power Sharing With Voltage Distortion Compensation of Droop Controlled Islanded Microgrids

Harmonics are found to have deleterious effects on power system equipment including transformers, capacitor banks, rotating machines, etc. However, the distributed generation interfacing converters (DICs) are able to improve power quality and system efficiency in case of adding a flexible control strategy. This paper describes the voltage distortion generated by nonlinear loads and proposes a new harmonic droop control to reduce the voltage harmonic distortion at the point of common coupling (PCC) and to share the harmonic power between parallel islanded inverters controlled by classical frequency droop method. The main objective it to effectively compensate the harmonic currents drawn by each DIC to supply the nonlinear loads in parallel with voltage harmonic damping at PCC. The operation principle of the proposed harmonic droop is explained in details. Modeling and stability analysis are developed in order to define the control parameters suitable for proper operation. Simulation and experimental results are presented to show the competence of the proposed algorithm in achieving harmonic power sharing and in improving the voltage harmonic distortion at the PCC.

A flexible control strategy of a renewable active generator to participate in system services under grid faults

A flexible control strategy of a renewable active generator to participate in system services under grid faults

Adaptive synchronization of multi-agent systems via variable impulsive control

This paper mainly focuses on the adaptive synchronization problem of multi-agent systems via distributed impulsive control method. Different from the existing investigations of impulsive synchronization with fixed time impulsive inputs, the proposed distributed variable impulsive protocol allows that the impulsive inputs are chosen within a time period (namely impulsive time window) which can be described by the distances of the left (right) endpoints or the centers between two adjacent impulsive time windows. Obviously, this kind of flexible control scheme is more effective in practical systems (especially for the complex environment with physical restrictions). Moreover, the proposed adaptive control technique is helpful to solve the problem with uncertain system parameters. By means of Lyapunov stability theory, impulsive differential equations and adaptive control technique, three sufficient impulsive consensus conditions are given to realize the synchronization of a class of multi-agent nonlinear systems. Finally, two numerical simulations are provided to illustrate the validity of the theoretical analysis.

A Flexible Control Strategy for Shore-to-Ship Power System in Terms of Grid-Connected and Off-Grid Switch

Abstract There are promising application prospects for applying the shore power technology to the ships in the port for the purpose of pollution prevention. However, the grid-connection of the shore power supply to the ship power grid leads to current surges, damages the ship power consumption equipment, and results in the instability of the ship power grid system, which will seriously affect the reliability of the operation of the ship power grid system. In order to address this problem, the mathematical model of virtual synchronous generator is introduced in this paper. Then, a control method for the flexible grid-connection of the shore power supply to the ship power grid based on the virtual synchronous generator is proposed. Next, the output characteristics of the shore power supply are optimized to match the characteristics of the ship generator, which contributes to the flexible grid-connection of the shore power supply to the ship power grid system. The effectiveness and the feasibility of this method are verified by simulation and experiments.

Flexible Control of Photovoltaic Grid-Connected Cascaded H-Bridge Converters During Unbalanced Voltage Sags

Multilevel cascade H-bridge (CHB) converters are one of the promising solutions for medium- and large-scale grid-connected photovoltaic power plants. However, there is a lack of a complete study about their operation during voltage sags. This paper proposes a flexible control strategy for the operation of photovoltaic grid-connected CHB inverters during unbalanced voltage sags. The key novelty is that the proposed strategy is able to inject both active and reactive powers to the grid with either balanced or unbalanced currents, while ensuring that all dc-link capacitor voltages remain balanced. The simulation and experimental evaluations of a 9-kVA grid-connected seven-level CHB illustrate and validate the performance of the proposed strategy for the operation of the grid-connected CHB converter during different unbalanced voltage sags.

A flexible control strategy with overcurrent limitation in distributed generation systems

Distributed Generation (DG) systems are typically interfaced with distribution lines by modern power converter devices, which their controllers and dynamic behaviours are significantly influenced by unbalanced grid faults. The active and reactive power control with positive-negative sequences (PNS) is one of fundamental of power converter control under grid fault conditions. This paper proposes a reference current generator (RCG) based flexible power control strategy to enable regulation of active and reactive power with minimizing active and reactive power oscillations. Current limitation control is embedded into the RCG in order to keep maximum current injection in safety limitation for overcurrent protection under grid faults and harmonic distortions. The proposed control strategy has been also accomplished maximum active power and minimum reactive power transfer capability to electric grid. The analytical expression of active and reactive power oscillations depending on flexible control parameters are comprehensively investigated as theoretically and examined with simulations. Fractional order proportional integral (FOPI) controller is preferred to minimise steady state error of AC current regulation and provide faster processing time instead of conventional PI and proportional resonant (PR) controllers. An important contribution for similar previous studies is that PNS voltage and current components are separated by dual average filter based phase locked loop (DAPLL) which is firstly proposed in this paper. The performance of proposed controller is compared with multiple complex-coefficients filter (MCCF-PLL) based controller. Theoretical analysis and simulation results verify the correctness and effectiveness of the proposed solution.

Automatic Positioned Controller Parabolic solar Dish Prototype

This paper discusses the development of dual axis parabolic dish tracker application for automatized position power system. This prototype tackles solar light in solar sterling design system or concentrated photovoltaic design by implementation of digitalize control circuit to enhance CSP and CPV applications. A normally 121.92cm dish is designed with H-bridge controller technique & Slew drive actuator mode to capture solar irradiances. The surface of dish is polished with 12 aluminum bars to concentrate the solar irradiance in one reflective axis. Economic justification for Pakistan’s industries would be possible if these automated based renewable prototypes are promoted in market in compare of single PV panel. This prototype controls the all weather conditions, utilizing real time flexible timing control strategy and photoelectric tracking scheme to provide cost effective product for industrial power generation applications. This locally adaptive material based prototype encouraged the result about 33% efficient with compared to photovoltaic panel.

Distributed Finite-Time Convergence Control of an Islanded Low-Voltage AC Microgrid

The control of an islanded AC microgrid with high penetration level of renewable generations is complicated and challenging due to its low inertia and fast changing operating conditions. To address the drawbacks of traditional droop control with low-voltage AC microgrid, an adaptive virtual impedance control is proposed to improve the active/reactive power sharing accuracy. To deal with the frequency and voltage deviation caused by the primary control while satisfying the fast response requirements and various users' preferences, a flexible distributed control strategy is proposed as the secondary control. The proposed control strategy can restore the frequency and voltage magnitude to the desired values in a finite-time manner, using only local and neighboring information. The finite-time convergence of the proposed distributed control algorithm is guaranteed through rigorous analysis. Simulation studies validate the effectiveness and scalability of the proposed distributed control strategy.