In this paper, a composite control strategy for improved off-grid configuration based on photovoltaic (PV array), a wind turbine (WT), and a diesel engine (DE) generator to achieve high performance ...while supplying nonlinear loads is investigated. To operate the WT efficiently under variable speed conditions and to obtain accurate and fast convergence to the maximum global operating point without a speed sensor, an iterative interpolation method is integrated with the perturbation and observation (P&O) technique. To ensure the balance of power in the system and to achieve the maximum power from the PV array without using any maximum power point tracking (MPPT) method, and ensuring stable operation during the disturbance, a double-loop control strategy for a two-switches buck-boost converter is developed. Furthermore, to protect the synchronous generator of the diesel generator (DG) from the 5th and 7th order-harmonics created by the connected nonlinear loads and to solve the issue of the filter resonance, the interfacing three-phase inverter is controlled using an improved synchronous-reference frame algorithm (SRF) with virtual impedance active damping. The presented work demonstrates effective and efficient control along with improved performance and cost-effective option as compared to the similar works reported in the literature. The performance of the presented off-grid configuration and its developed composite control strategy are tested using MATLAB/Simulink and validated through small-scale hardware prototyping.
A seven-level modified packed U-cell (MPUC7) based static synchronous compensator (MPUC7-STATCOM) with an autotuned finite control-set model predictive control (AFCS-MPC) is introduced in this ...article. MPUC7-STATCOM is a compact four-quadrant cascaded topology that comprises merely six switches and two isolated dc capacitors. Thus, in comparison with a seven-level cascaded H-bridge (CHB) based STATCOM, not only the proposed configuration has exceptionally reduced active/passive component count, but also MPUC7-STATCOM designed AFCS-MPC control method complexity is attenuated meaningfully. Boost-mode operation and low voltage rating of the components can be also mentioned as the merits of the MPUC7-STATCOM. Using the proposed AFCS-MPC, nonlinearities of the MPUC7 converter have been considered and both capacitors' voltages are directly regulatable at different desired amounts accurately. Moreover, the weighting factors of the proposed AFCS-MPC are tunable automatically in real-time. Consequently, MPUC7-STATCOM has a desirable dynamic operation and its capacitors' values are reduced. Provided simulation and experimental results validate the viability of the MPUC7-STATCOM topology and robustness of the designed AFCS-MPC method as well as its steady-state and dynamic operation.
This paper proposes a fast repetitive control (FRC) scheme with harmonic correction loops for the three-phase three-wire shunt active power filter (APF) applied in weak power grid. The FRC scheme ...consists of a repetitive control loop which is designed in the synchronous rotational frame and a fractional delay (FD) filter for approximating the FD caused by the fixed sampling rate. It can significantly improve the dynamic performance for the harmonic compensation. In weak grid situation, the grid frequency, voltage and then harmonic currents would vary rapidly with disturbances. A cumulative error cancellation loop is introduced into the FRC to improve the harmonic detection accuracy when grid frequency drifts. The harmonic correction loops are proposed to correct the harmonic references with selected orders when they vary rapidly with the grid voltage. With such loops, the compensation precision of the shunt APF can be highly improved. Simulation and experiment results verified the effectiveness of the proposed scheme.
This paper introduces a new concept of optimal utilization of a unified power quality conditioner (UPQC). The series inverter of UPQC is controlled to perform simultaneous 1) voltage sag/swell ...compensation and 2) load reactive power sharing with the shunt inverter. The active power control approach is used to compensate voltage sag/swell and is integrated with theory of power angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. Since the series inverter simultaneously delivers active and reactive powers, this concept is named as UPQC-S (S for complex power). A detailed mathematical analysis, to extend the PAC approach for UPQC-S, is presented in this paper. MATLAB/SIMULINK-based simulation results are discussed to support the developed concept. Finally, the proposed concept is validated with a digital signal processor-based experimental study.
In this paper, the design and implementation of active power control with antiwindup PI controller (AWPI) and improved perturbation and observation (P&O) method with sliding mode control (SMC), are ...investigated to get a high level of performance with a reduced number of sensors for a stable operation of a wind-PV-battery-based hybrid standalone power generation system (HSPGS). The SMC approach with boundary layer is used for an optimum trajectory on the sliding surfaces, with variable operating conditions of many power converters connected at the same DC bus. Furthermore, detailed modeling and stability analysis to demonstrate the transversality, reachability, and equivalent control are presented. The effectiveness and robustness of HSPGSs and their respective control strategies are validated by simulation and test results on a hardware prototype using a DSP-dSPACE real time controller.
In this article, an implementation of solar photovoltaic (PV) array powered grid-connected residential electric vehicle (EV) charger is presented, which caters the need of an EV, household loads, and ...the grid. The charger is enabled to operate autonomously using a PV array for providing an uninterruptible charging and power to household loads. However, in the absence of the PV array or insufficient PV array generation, the grid-connected mode of operation is presented. Moreover, the charger is supported with the synchronization and seamless mode switching control, so that the charger automatically connects/disconnects from the grid without disturbing the EV charging and household supply. The charger is also enabled with the vehicle-to-grid active/reactive power support to the grid and vehicle-to-home power transfer for supporting the local loads in an islanded condition. The charger is also controlled to operate as an active power filter for achieving the unity power factor operation and total harmonic distortion of the grid current within 5%. Moreover, for achieving energy management, a dc-link voltage regulation based energy management strategy is used and a sliding mode control is used for regulating the dc-link voltage. For satisfactory operation under distorted voltage condition, a second-order generalized integrator frequency-locked loop with dc offset rejection is used to generate the sinusoidal reference grid current. The charger is designed for a single-phase 230-V, 50-Hz grid and it is experimentally validated in the laboratory.
This paper deals with a modified technique for the recognition of single stage and multiple power quality (PQ) disturbances. An algorithm based on Stockwell's transform and artificial neural ...network-based classifier and a rule-based decision tree is proposed in this paper. The analysis and classification of single stage PQ disturbances consisting of both events and variations such as sag, swell, interruption, harmonics, transients, notch, spike, and flicker are presented. Moreover, the proposed algorithm is also applied on multiple PQ disturbances such as harmonics with sag, swell, flicker, and interruption. A database of these PQ disturbances based on IEEE-1159 standard is generated in MATLAB for simulation studies. The proposed algorithm extracts significant features of various PQ disturbances using S-transform, which are used as input to this hybrid classifier for the classification of PQ disturbances. Satisfactory results of effective recognition and classification of PQ disturbances are obtained with the proposed algorithm. Finally, the proposed method is also implemented on real-time PQ events acquired in a laboratory to confirm the validity of this algorithm in practical conditions.
This paper proposes sensorless control strategies for an offshore wind farm (OWF) and voltage source converter high voltage direct current (VSC-HVdc) stations. The extended Kalman filter provides an ...estimation of the speeds and rotor positions of permanent magnet synchronous generators (PMSGs) of OWF, the dc voltage at dc-bus and the dc voltages of the both VSC-HVdc stations. The OWF, composed of 150 variable speed wind turbines based on PMSGs, is considered in this paper, where each generator is connected in series by its own ac-dc converter to dc-bus. Only one dc-ac inverter converts the dc-bus voltage to a proper ac voltage of wind farm ac-bus. The HVdc transmission system based on a three-level neutral point clamped VSC is used for the interconnection between the OWF and the onshore grid via two dc cables. Detailed modeling and control strategies are developed for each individual component of the system. Simulation results show the effectiveness of the proposed method to manage the desired HVdc system operation.
In this article, a solar photovoltaic (PV) array, a battery energy storage (BES), a diesel generator (DG) set, and a grid-based electric vehicle (EV) charging station (CS) is utilized to provide the ...incessant charging in islanded, grid-connected, and DG set connected modes. The CS is primarily designed to use the solar PV array and a BES to charge the EV battery. However, in case of exhausted storage battery and unavailable solar PV array generation, the CS intelligently takes power from the grid or DG set. However, the power from DG set is drawn in a manner that it always operates at 80%-85% loading to achieve maximum fuel efficiency under all loading conditions. Moreover, in coordination with the storage battery, the CS regulates the generator voltage and frequency without a mechanical speed governor. It also ensures that the power drawn from the grid or the DG set is at unity power factor even at nonlinear loading. Moreover, the point of common coupling voltage is synchronized to the grid/generator voltage to obtain the ceaseless charging. The CS also performs the vehicle to grid active/reactive power transfer, vehicle to home, and vehicle-to-vehicle power transfer for increasing the operational efficiency of the CS. The operation of the CS is experimentally validated using the prototype developed in the laboratory.
The precise information of permanent-magnet synchronous generator (PMSG) rotor position and speed is essentially required to operate it on maximum power points. This paper presents an adaptive ...network-based fuzzy inference system (ANFIS) for speed and position estimation of PMSG, where an ANFIS-based model reference adaptive system is continuously tuned with actual PMSG to neutralize the effect of parameter variations such as stator resistance, inductance, and torque constant. This ANFIS-tuned estimator is able to estimate the rotor position and speed accurately over a wide speed range with a great immunity against parameter variation. The proposed system consists of two back-to-back connected inverters, where one controls the PMSG, while another is used for grid synchronization. Moreover, in the proposed study, the grid-side inverter is also utilized as harmonic, reactive power, and unbalanced load compensator for a three-phase, four-wire (3P4W) nonlinear load, if any, at point of common coupling (PCC). This enables the grid to always supply/absorb a balanced set of fundamental currents at unity power factor. The proposed system is developed and simulated using MATLAB/SimPowerSystem (SPS) toolbox. Besides this, a scaled laboratory hardware prototype is developed and extensive experimental study is carried out to validate the proposed control approach.
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