Three-phase AC Loads Research Articles

Energy management based on a fuzzy controller of a photovoltaic/fuel cell/Li-ion battery/supercapacitor for unpredictable, fluctuating, high-dynamic three-phase AC load

Introduction. Nowadays, environmental pollution becomes an urgent issue that undoubtedly influences the health of humans and other creatures living in the world. The growth of hydrogen energy increased 97.3 % and was forecast to remain the world’s largest source of green energy. It can be seen that hydrogen is one of the essential elements in the energy structure as well as has great potential to be widely used in the 21st century. Purpose. This paper aims to propose an energy management strategy based a fuzzy logic control, which includes a hybrid renewable energy sources system dedicated to the power supply of a three-phase AC variable load (unpredictable high dynamic). Photovoltaic (PV), fuel cell (FC), Li-ion battery, and supercapacitor (SC) are the four sources that make up the renewable hybrid power system; all these sources are coupled in the DC-link bus. Unlike usual the SC was connected to the DC-link bus directly in this research work in order to ensure the dominant advantage which is a speedy response during load fast change and loads transient. Novelty. The power sources (PV/FC/Battery/SC) are coordinated based on their dynamics in order to keep the DC voltage around its reference. Among the main goals achieved by the fuzzy control strategy in this work are to reduce hydrogen consumption and increase battery lifetime. Methods. This is done by controlling the FC current and by state of charge (SOC) of the battery and SC. To verify the fuzzy control strategy, the simulation was carried out with the same system and compared with the management flowchart strategy. The results obtained confirmed that the hydrogen consumption decreased to 26.5 g and the SOC for the battery was around 62.2-65 and this proves the desired goal.

Feature-Reduced Stability Analysis of Islanded Photovoltaic Microgrid Inverters

A smart grid environment is prone to data explosion while controlling a microgrid system. Islanded Microgrid’s stability analysis involves a large number of system state variables thus consuming more computational memory due to parallel connected inverter dynamics. Parallel inverters generate reference voltage and frequency using droop controllers, unlike grid-connected inverters where the primary grid provides the reference voltage and frequency. This paper develops feature-reduced stability analysis of the parallel inverters thus reducing the computational memory of its stability analysis. Principal component analysis being a feature extraction technique is applied to reduce the number of variables determining stability. MATLAB is used to develop the average model of a parallel inverter with an LCL filter and a three-phase AC load. Evaluation of the stability analysis using the state variable analysis with the virtual resistance method is simulated. Simulation validates stability analysis of the model with reduced state variables. An average model developed using MATLAB and PCA carried out using Python clearly indicated the validation of the dimensionality reduction in the stability analysis. The reduced number of variables is validated for a stable range of the parallel inverter droop controller. Both cases validated the dimensionality reduction in the stability analysis of parallel inverters.

Finite control set model predictive control approach of nine switch inverter-based drive systems: Design, analysis, and validation

This paper describes a model predictive control method for Nine-Switch Inverter (NSI)-based AC drive systems. Two separate three-phase AC loads (dual-output mode operation) or a single six-phase load (six-phase mode operation) can be connected to output terminals of an NSI. Three different Finite Control Set Model Predictive Control (FCS-MPC) strategies are presented and described. Firstly, dual-output mode FCS-MPC provides flexible control of detached load stages without any undesirable interaction. When disseminated loads are needed to be controlled, the output terminals of NSI are individually connected to separate load stages. Secondly, six-phase mode FCS-MPC provides robust control of six-phase load current. Thirdly, the predictive control scheme for controlling multiple induction machines is presented. Experimental and simulation tests have demonstrated that the proposed method exhibits a secured converter operation. The proposed predictive control strategies of Nine-Switch Inverter are accomplished using a Field Programmable Gate Arrays (FPGA).

Model predictive control of nine-switch converter with output filter for independent control of two loads

This paper proposes a model predictive control (MPC) algorithm designed for nine-switch converter with output filter (NSCOF) to control two three-phase AC loads independently. A state function of each leg of nine-switch converter (NSC) is established to characterize the internal conditions of the NSC because the traditional model of the NSCOF does not involve the interior model of the NSC. Based on the NSCOF model with the state function of each leg, a prediction model of NSCOF is constructed. The two AC terminals of NSCOF are treated as one module when the MPC is designed. The proposed MPC achieves controlling two three-phase AC loads working under different frequency modes. Furthermore, this algorithm is independent of the modulation method for reducing the difficulty of the controller design and its limits. The simulation and experimental results reveal that the steady-state and dynamic response performance of NSCOF are substantially improved using MPC.

Experimental Validation of Shared Inverter Topology to Drive Multi AC-Loads

Many reduced-switch-count (RSC) inverter topologies have been proposed in the literature. As the number of switches required to produce a set of voltages in RSC inverters are less than that in conventional inverter, as a result utilizing RSC inverters in a certain system reduces its size and cost. In this paper, a novel RSC shared inverter topology consisting of fifteen switches and capable of driving four three-phase AC-loads independently is proposed and experimentally verified. A carrier-based pulse width modulation (PWM) technique that employs the zero-sequence-signal injection principle is developed to drive the proposed inverter along with adequate DC voltage bus utilization between the shared loads for common frequency (CF) as well as different frequency (DF) modes. The structure and the principle of operation of the proposed inverter are introduced and intensively verified using simulation and field-programmable-gate-array (FPGA)-in-the-loop simulation under linear and nonlinear loads. Then, Inverter prototype was built and the proposed inverter has been verified experimentally. The experimental results verify the applicability of the proposed inverter and the employed PWM.

A Multiport AC Link PV Inverter With Reduced Size and Weight for Stand-Alone Application

In this paper, a multiport high-frequency ac link inverter is proposed as the power electronic interface between the photovoltaic (PV) modules, battery energy storage system, and three-phase ac load. In this inverter, a single-stage power conversion unit fulfills all the system requirements, i.e., inverting dc voltage to proper ac, stepping up or down the voltage, generating low harmonic ac current at the output, and input/output isolation. The ac link is formed by a parallel ac inductor/capacitor <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(LC)$</tex></formula> pair having low reactive ratings. A single-input/single-output partial resonant inverter has already been proposed by the present authors. This paper verifies the possibility of extending this topology to multiport partial resonant converters. The proposed converter is believed to overcome most of the shortcomings associated with the currently available multiport PV inverters. It is a single-stage ac link power conversion system with zero voltage turn on and soft turn off of the switches, which has very small switching losses, compact size, and light weight. The proposed converter does not contain any electrolytic capacitors at the link, which increases the reliability of this converter to a great extent. In the proposed inverter, PV side and ac side are isolated; however, if galvanic isolation is required, a single-phase high-frequency transformer can be added to the link. This converter can both step up or down the voltage, regardless of the presence of a transformer. Although this configuration is extendable to the grid-connected applications, in this paper, only the stand-alone application is considered. The performance of the proposed multiport inverter is verified through simulations and experiments.

Matching three-phase AC loads to PVG for maximum power transfer using an enhanced version of the Akbaba model and double step-up converter

The matching of three-phase AC loads to photovoltaic generators (PVGs) for maximum power transfer using an enhanced version of the Akbaba model for I– V characteristic of PVGs is investigated. With an enhanced version of the Akbaba model, the model parameters are expressed directly in terms of percent solar radiation. With this improvement on the Akbaba model, only a single input, which is the percent solar radiation for a particular location on the globe, is required for the calculation of the complete performance of the PVG-load system, including available maximum (peak) power. With this new approach all previously needed iterative calculations to determine system performance are eliminated. As an application example, this new approach is applied to the matching of a three-phase load to PVG for maximum power transfer through a double DC–DC step-up converter and a six-step inverter. The effectiveness and accuracy of the model is demonstrated through detailed numerical results.

Robust current controller for three-phase inverter using finite-state automaton

A novel feedback current controller for a three-phase load driven by a power inverter is proposed. The main design specifications are robustness to load electrical parameters, fast dynamical response, reduced switching frequency, and simple hardware implementation. To meet previous specifications a multi-variable hysteresis type controller is proposed, designed as a finite-state automaton and implemented with a programmable logic device. After a general introduction, system analysis is performed, control targets are specified, and the proposed control strategy is presented and discussed. Further, actual controller architecture, based on simple analog-logic hardware, is shown and experimental results are presented using an induction motor as the inverter load. However, this does not limit the wider applicability of the proposed controller that is suitable for different types of three-phase AC loads. >