Microsoft Word - ETASR_V12_N4_pp8960-8966 Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8960-8966 8960 www.etasr.com Nebili et al.: Decoupling Control Applied to the Smart Grid Power Dispatching Problem Decoupling Control Applied to the Smart Grid Power Dispatching Problem Salim Nebili Department of Physics, Laboratory of Electrical and Energetic Systems, Faculty of Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia salim.nebili@tunisietelecom.tn Ibrahim Benabdallah Department of Physics, Laboratory of Electrical and Energetic Systems, Faculty of Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia ibrahim.benabdallah@gmail.com Adnen Cherif Department of Physics, Laboratory of Electrical and Energetic Systems, Faculty of Sciences of Tunis, University of Tunis El Manar, Tunis, Tunisia adnen2fr@yahoo.fr Received: 15 May 2022 | Revised: 9 June 2022 | Accepted: 13 June 2022 Abstract-This paper presents controller designs of the decoupling issue dedicated to renewable decentralized generators or new generation grids known as smart grids. The control methods were based on a three-phase voltage source grid representation that integrated wind and photovoltaic generators. The utilized decoupling strategies (Boksenbom and Hood, Zilkind and Luyben, and inverted decoupling) allowed the optimization of energy transfers and costs through the routing grid distribution path. Simulations were conducted in Matlab/Simulink. The trustworthiness of the multivariable control system design in addition to the tuning method was established using three test batches, totally decoupled and stable from input dependencies. Keywords-decoupling; smart grid; demand-response; power dispatching; controller design I. INTRODUCTION Methods presenting only one output controlled by a single deployed variable are classified as Single-Input Single-Output (SISO) systems. Several processes do not imitate such a simple control shape. Each unit operation needs to control no less than two variables, and consequently, there are frequently at least two control loops to deal with. Systems that involve more than one control loop are known as Multi-Input Multi-Output (MIMO) or multivariable systems. The electrical smart grid is essentially a massive MIMO system. Due to the interactions of the flow power offer and demand, it is not easy to design a robust controller for each path autonomously to lead an input x to an output y without affecting any other output. Many studies have focused on several loop control structures to diminish these interactions. Decoupling methods are mostly used in industrial processes but are still applicable for many electrical system parameter- decoupling purposes. A simplified, ideal, and inverted decoupling comparative study was presented in [1], which was the base for many classic studies. Three decoupling methods were considered to deal with stability, robustness, and implementation aspects, while the complexity of the decoupler elements depended on the overall system size. An improvement of the two inverted decoupling methods was presented in [2] for the case of a stable linear multivariable class of processes, through no minimum-phase zeros and multiple time delays. As some multivariable processes were still unable to be decoupled due to stability issues, alternative decoupling with a unity feedback structure was suggested. The PI/PID was designed using internal model control to decouple the processes. In the case of multiplicative input uncertainty, the low bounds of the control parameters were intended to guarantee the robust stability of the system. As the disturbances influence the way of the control synthesis of a MIMO system based on ideal decouplers and a PID regulator, single controller performance and robustness from the closed-loop could be prolonged to all loop systems [3]. An improved decoupling approach allowed more flexibility in the choice of transfer functions of the decoupled apparent process for general n×n processes, where the decoupler elements’ complexity appeared independent of the system's size [4]. A decoupling internal model controller design method was proposed in [5] for industrial MIMO time- delay systems, based on a controlled model adjoint matrix. A decoupling compensator and an internal model controller, Butterworth low-pass filter, were designed for decoupling the generalized controlled object. The last filter aimed to improve the disturbance rejection aptitude. In [6], a method of finding the forced oscillation source was proposed. The relation between the observable outputs and the mechanical power problems in a unit was decoupled by sensibly designing a Luenberger observer using an aging structure task. A MIMO control system with multiple time delays and a model predictive control was presented in [7], describing a method to design MIMO filtered Smith predictors for n×n processes through multiple time delays based on the decentralized direct decoupling structure. This allowed simple tuning of the primary controller, making simpler the problem toward multiple single loops, if realizable, and it could also be used to eliminate the interactions among process variables. The decoupling method is also applicable to electrical grid, microgrid, and smart grid annexed domains facing new intermittent and highly variable system challenges and expectations [8-17]. Modeling approaches were proposed in [8] using analytical tools for control design purposes of step-up grid-connected PV systems, such as voltage source Corresponding author: Salim Nebili Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8960-8966 8961 www.etasr.com Nebili et al.: Decoupling Control Applied to the Smart Grid Power Dispatching Problem representation of the bulk capacitor interacting with the grid- connected inverter and considering the inverter of a double- stage PV system as a Norton equivalent. Furthermore, both ideal and real DC/DC converter models for the PV module were presented through four mathematical models, stated in state-space representation. A decoupled inverter connected to a grid was exposed in [9], using dynamic online grid impedance measurements in a micro grid application. The controller was implemented in a synchronous reference frame and PI controllers were used, while mutual coupling was introduced between the d and q control loops. The transformation into a synchronous reference was accurately decoupled using the dynamically measured grid impedance and feedforward control. Decoupling permits autonomous control of active and reactive powers following changes, and online real impedance measurement was proposed to make the decoupling more precise. In [10], a multivariable-droop synchronous current converter decoupling control strategy was proposed for the current management of weak grid/micro grid applications, offering a traditional forward design method that employs the loop determining technique. The controller mixes current regulation, management, and limitations that apply to weak and micro grids. The multivariable synchronous current converter allowed larger decoupling of d- and q-axis currents in weak and/or resistive grids, anywhere these control variables are highly coupled due to the converter’s large load-angle operation. In [11], the evolution allocation for the decoupling of the electrical network was studied using pure channel component transform, addressing issues such as robustness. Difficulties were efficiently overcome using singular values instead of proper decomposition. An algorithm was developed to show how the adopted transformation can be used for voltage stability analysis. In [12], a distributed generator strategy control was investigated to assist a conventional local grid by decoupling phase sequences, frequency domain unbalances, and harmonic compensation for grid-connected inverters through unbalanced loads. This strategy was considered sequential-asymmetric for unbalanced and harmonic voltage correction. Moreover, a Norton equivalent model in frequency- domain was used. This study showed that following a frequency-domain decoupled method, the fundamental positive, harmonic symmetrical, fundamental zero, and negative sequence components can be regulated independently. In [13], a virtual synchronous generator control method was proposed for extensive renewable energies connected to a grid. A power decoupling control method based on linear active disturbance rejection control was developed to eliminate output power deviation. Using the coupling term estimates and disturbances from an extended state observer, the aforesaid matter triggered by power coupling can be lessened. Furthermore, the stability of the controller was analyzed. In [14], essential limitations were defined for the islanded mode of operation of micro grids which cannot be absorbed by conventional FP methods. Therefore, updates were designed for conservative approaches by including network frequency as a variable and avoiding the network soft bus. These particular aspects of the Newton-Raphson method modified the designs of the Jacobean matrix. Extended power factor equations were decoupled by reformulating the Jacobean matrix based on the fact that lines are mostly resistive. Furthermore, two convergence improvement methods were also incorporated. Dual-buck inverters were examined in [15], reassessing volume, system weight, and power density of dual-buck single- phase grid-tied PV inverters. A new active power decoupling buffer and grid-tied photovoltaic inverter integration with single-inductor dual buck topology were proposed, using a single-loop direct input current ripple control method. Several concerns arise in the case of pulse width modulation using a high-voltage current source converter based on fully controlled devices, such as high switching losses, large DC voltage fluctuations, and thin power operation range [16]. To resolve these difficulties, a current source converter-based HVDC was proposed using fundamental frequency modulation presenting the topology, an independent control strategy, and a mathematical model. A synchronized control strategy was proposed to decouple active and reactive powers with an outer and inner current controller loop to lead to lower DC voltage fluctuations, lower switching losses, and a broader power operation range. This study investigated a Two-Input Two-Output (TITO) grid system, as a MIMO system could be devised into several TITO subsystems. The main goal was to employ decoupling methods for grid part energy aggregation, aiming to decouple demand response paths based on statue and output feedback control methods. II. CONTROLLER DESIGN AND METHODS The control strategy of the phase grid-connected PV, wind, and storage system inverter is presented in Figure 1. The elements were taken from [17-24]. Fig. 1. Overall grid-connected system design. The system can be described in the state representation by: ��. � �� � �� � � � �� (1) where A is the characteristic matrix, B is the order matrix, C is the output matrix, and D is the coupling matrix. A control law was defined by the output feedback as: � � � �. � (2) Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8960-8966 8962 www.etasr.com Nebili et al.: Decoupling Control Applied to the Smart Grid Power Dispatching Problem where V is the new entries vector of the dimension (m.1), K is the matrix of dimension (m.l), m is the number of outputs, l is the number of entries, y is the output vector, and e is the input vector. K is calculated by solving: |�� � �� | � 0 (3) The governing equations of the network filter defined in Figure 1 are: ⎩⎪⎨ ⎪⎧������� � ���� � � � ��� �� �� � �!�! � ! � �!�"��"�� � �#�# � # � �# (4) The fundamental principles of simplification of the equations of states, such as the Park model, can be used to either substitute or eliminate the effect of one or several equations, to implement and succeed in the decoupling methods by delimitating the effects of inputs on outputs. The relative Park equation model from the overall grid-connected system design is given by: $�%��%�� � �� �� � � � ���&��&�� � �' �' � ' � �' (5) Input and output voltages are linked by values belonging to ℝ: � � � �� �� � �' �' ' � (� �� � (' �' (6) Using (5): $�%��%�� � ��� �� � � � ���&��&�� � ��' �' � ' � �' (7) Substituting (6) in (7) gives: �%��%�� � ��� �� � )�� �� � �' �' * � ���&��&�� � ��' �' � )(� �� � (' �' * � �' (8) � � +,-%�% 00 ,-&�& . , � � / )�,0%*�% ,0&�%,1%�& 2�,1&3�& 4 � 51 00 17 , � � 50 00 07 (9) The transfer function matrix G(s) can be easily obtained from the state representation using: 8)9* � )9� � �*,�� � � (10) In the general case, the matrix D is null and the calculation of G(p) is simplified as: 8)9* � )9� � �*,�� (11) 8)9* � :8�� 8�!8!� 8!!; (12) The used units are L1 = L2 =16.58.10 -3 H, and r1 = r2 = 0.98Ω. The transfer matrix is obtained from the A, B, and C matrices: 8)9* � + <.<=>�< <.<=>�<,<.