Load Current Sensor Research Articles

Nonsingular fast terminal sliding mode control for two-stage converters of AC island photovoltaic microgrid

Taking into account almost all kinds of variations and uncertainties to which AC island photovoltaic (PV) microgrid is often subjected, this paper proposes a new nonsingular fast terminal sliding mode control (NFTSMC) strategy for two-stage converters to enhance robustness against those disturbances and improve system dynamic performance. Firstly, to effectively decrease the adverse effect on the system from intermittent solar irradiation and uncertain environmental temperature, a NFTSMC cascaded with perturb and observe (P&O) scheme is put forward for fore-stage DC/DC converter, and PV output voltage is controlled to track its reference and thus maximum power point tracking (MPPT) performance is improved. Then, to significantly decrease the adverse effect on the system from variations of load and LC filter parameters, by incorporating an extended state observer (ESO) into NFTSMC, an ESO-based NFTSMC scheme is proposed for post-stage DC/AC converter, and the load voltage is regulated to track its reference and thus system robustness is strengthened, in which ESO is designed to replace load current sensor and thus reduce hardware cost. By using global terminal attractor without discontinuous switching function, the proposed NFTSMC strategy can not only strengthen system robustness but also improve system dynamic performance. Lastly, on account of the variations of PV generation and load demand, a conventional double-loop PI scheme is put into use for bidirectional DC/DC converter and thus system power balance is ensured. Comprehensive MATLAB simulation and StarSim/Hardware experiment results show that the proposed NFTSMC strategy for two-stage converters can overcome negative effects caused by various internal and external disturbances, and thus enable island PV microgrid to operate reliably and supply high-quality AC power.

Coordinated Control for Performance Enhancement of an Islanded AC/DC Microgrid With Uninterrupted Power and Seamless Transition Capabilities

This article presents a simplistic control approach and multimode operation of a wind-solar-based ac/dc microgrid. The islanded microgrid consists of a doubly-fed induction generator (DFIG) for wind energy conversion, and a solar photovoltaic array for solar energy conversion. In this configuration, the stator terminals of DFIG are connected at the point of common intersection (PCI) of ac loads via a stator-side solid-state transition switch ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SSTS</sub> ). The developed control strategy is designed to seamlessly disconnect and reconnect the DFIG stator from the PCI based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SSTS</sub> operation, without interrupting power to ac and dc loads in the microgrid. The disconnection of stator terminals is required in the event of a prolonged period of no wind generation from the DFIG. The controller is synthesized to ensure no or low transient effect during the transition between the two operating modes, i.e., DFIG stator connected mode (SCM) and stator disconnected mode (SDM). Further, the power quality enhancement of stator voltages and currents amidst nonideal ac loads is ensured without need for computationally exhaustive approaches involving sequence decompositions, notch filters, resonant regulators, or load current sensors. Moreover, the power quality enhancement at the DFIG stator is achieved without injecting any undue harmonics in the DFIG rotor currents. The effectiveness of this islanded microgrid is verified through obtained results from a developed laboratory prototype.

Experimental verification of STATCOM based on quasi impedance source inverter for power quality enhancement in the hybrid distributed generation system

PurposeThis paper aims to introduce the quasi impedance source inverter (qZSI)-based static compensator (STATCOM), which is incorporated into the hybrid distributed power generation system for enhancement of power quality. The distributed power generation system includes the photovoltaic (PV), wind energy conversion system (WECS) and battery energy storage system.Design/methodology/approachThe WECS is used by the self-excited induction generator (SEIG) and the flywheel energy storage system (FESS). To regulate its terminal voltage and frequency, the SEIG requires adjustable volt-ampere reactive (VAR). A combination of a STATCOM and a fixed condenser bank usually serves to satisfy the VAR demand. The maximum correntropy criterion-based adaptive filter technique (AFT) is proposed to control the qZSI-STATCOM and to guarantee that the voltage at the SEIG terminal is harmonic-free while providing non-linear three-phase and single-phase loads.FindingsThe coordinated operation of the suggested voltage control and flywheel control systems ensures that load voltage and frequency are retained in their respective values at very low harmonic distortions regardless of wind speed and load variation. The simulation and experimental studies are carried out under different load conditions to validate the efficiencies of the PV-assisted STATCOM.Originality/valueTo improve system stability and minimize total costs, extra load current sensors can also be avoided. This paper proposes to control the SEIG terminal voltage and harmonic elimination in the standalone WECS systems using maximum correntropy criterion-based AFT with a fuzzy logic controller.

Multilayer Model Predictive Control for a Voltage Mode Digital Power Amplifier

The application of the finite control set model predictive control to cascaded inverters is severely limited by its computational complexity. In this paper, a load observer based multilayer model predictive control is proposed for the voltage mode digital power amplifier employing cascaded full-bridge neutral point clamped inverter, which can avoid the use of load current sensor and greatly reduce the controller computation without affecting its dynamic performance. The discrete mathematical model of the voltage mode digital power amplifier employing cascaded full-bridge neutral point clamped inverter is established with filter inductor current and filter capacitor voltage as state variables. A load current observer is designed based on this to avoid the use of load current observer. Based on the discrete model and the observed load current, the upper layer of the multilayer model predictive control determines the optimal level that minimizes the cost function. The middle layer allocates the optimal level to each submodule in order to achieve capacitor voltage balancing. The lower layer determines the switching state of each submodule in order to reduce switching actions. Finally, the experimental results based on the designed nine-level prototype show that the develop multilayer model predictive control lead to acceptable steady state, dynamic and robust performance, with only 1.37% of the run time of the traditional model predictive control.

Development of Supercapacitor-Aided Hybrid Energy Storage System to Enhance Battery Life Cycle of Electric Vehicles

This paper presents a C-rate control method for a battery/supercapacitor (SC) hybrid energy storage system (HESS) to enhance the life cycle of the battery in electric vehicles (EVs). The proposed HESS provides satisfactory power for dynamic movements of EVs (e.g., acceleration or braking) while keeping the battery current within a secure level to prevent it from degradation. The configurations of conventional HESSs are often complex due to the two energy storages and their current/voltage sensing involved. Therefore, in this paper, a simple current-sensing scheme is utilized and the battery is directly treated as a controlled variable to help the battery output current remain stable for different load conditions. While the proposed circuit requires only one current feedback signal, neither the SC nor load current sensors are needed, and the circuit design is thus significantly simplified. Both simulation and experimental results validated the effectiveness of the proposed HESS operating in conjunction with the motor drive system. The proposed method aims at fully utilizing recycled energy and prolonging battery lifespan.

On the figure of merit and streamwise flow of a propulsive rotor with synthetic jets

Increasing the figure of merit of propulsive rotors for vertical takeoff and landing (VTOL) vehicles is critical to improving the hover efficiency and flight endurance of rotorcraft. In this paper, a new flow control scheme is proposed where 60 synthetic jet actuators are utilized on a large-scale propulsive rotor and the jets' velocity is increased from the blade root to the blade tip in order maintain constant levels of momentum coefficient per blade module. The three-bladed rotor measures 2.58 m in diameter and contains a NACA 0012 airfoil with zero blade twist distribution. The rotor was tested at speeds of 250, 500, 750 and 1,000 revolutions per minute (RPM) and blade pitch angles of 2, 5, and 8 degrees. Rotor thrust and power were measured using a high-capacity load cell and current sensor, and the streamwise flow was measured using phased-locked laser Doppler velocimetry (LDV) techniques at two measurement planes near the blade root and near the blade tip along the suction surface of the airfoil. Two flow control schemes were tested and compared; the new constant momentum coefficient (constant Cμ) and non-constant Cμ where the synthetic jet velocity is held constant throughout the rotor blade. When all 20 synthetic jets per blade are activated, it was found that constant Cμ improves low-speed rotor performance in terms of figure of merit, FM and thrust coefficient, CT at 250 RPM, while non-constant Cμ is marginally superior at higher rotor speeds. When both flow control schemes are applied for just the blade root module, an increase in performance compared to the baseline is observed at rotor speeds of 750 and 1000 RPM, however different values of FM and CT are achieved for each scheme. Near the blade tip the boundary layers undergo transition to turbulent flow combined with an increasing degree of adverse pressure gradient with rotor speed and blade pitch angle. Under these conditions where the normalized streamwise velocity profiles show significant velocity deficit in the near-wall flow, synthetic jets provide some momentum to delay separation as quantified by the boundary layer shape factor.

Modified Control Strategy for Shunt Active Power Filter With MRAS-Based DC Voltage Estimation and Load Current Sensor Reduction

Failure of any sensor involved in the operation of shunt active power filter (SAPF) not only degrades its performance but also deteriorates power quality. The purpose of the proposed technique is to eliminate load current, dc voltage, and filter current sensors, thus reducing the hardware cost of SAPF. In addition to the load and filter current sensor reduction, this article proposes a new dc voltage estimation technique, which will be used to eliminate the dc voltage sensor present in conventional SAPF. The proposed dc voltage estimation technique is based on model reference adaptive system (MRAS). A comparative analysis of the conventional SAPF (i.e., including all sensors) is performed with the proposed sensor reduction method to verify the effectiveness of the proposed method. Stability and sensitivity analysis of the estimation technique is performed in detail. The proposed work is simulated on the MATLAB/SIMULINK platform under various load conditions and disturbances. Further, it is validated on OPAL-RT 5700 platform.

Lyapunov-Based Large-Signal Control of Three-Phase Stand-Alone Inverters With Inherent Dual Control Loops and Load Disturbance Adaptivity

In this article, existed Lyapunov-based control methods for stand-alone inverters either have a single control loop accompanied with steady-state errors or dual control loops at the sacrifice of negative definiteness of the derivative of the Lyapunov function. Besides, load-current sensors or observers are indispensable in these methods. Proposed Lyapunov-based control inherently has dual control loops that can rigorously guarantee the global large-signal stability of the system. Meanwhile, load disturbance is suppressed adaptively without any load-current sensors or observers. Stability analysis proves that the proposed method is valid both for a linear and nonlinear load. The proposed approach complies with the internal model principle, leading to the minimized steady-state error. An adaptive weighted Lyapunov function (V) is proposed to derive the dual-loop control law and adaptive law. The closed-loop system is inherently d-q decoupled. Three controller gains are tuned quantitatively via explicit formulas based on pole-placement strategy. Simulation and experimental results demonstrate that the proposed method has good steady-state and dynamic performance with great robustness against the parametric mismatch.

Robotic Gripper With Force Feedback System

The aim of the project is to design an accurate responsive robot gripper that is capable of measuring the grasp force exerted on the object and varying its grasp force depending the material of the object. A parallel gripper is used which is actuated by a servo motor. The force is measured by mounting the force sensor on one finger of the gripper and the current to the servo motor is measured by a load current sensor. Hence by combing the force measured with the load current consumption of the servo motor, a control system is designed which will help in adjusting the grasp force of the gripper.

Improved DC-Link Voltage Regulation Strategy for Grid-Connected Converters

In this article, an improved dc-link voltage regulation strategy is proposed for grid-connected converters applied in dc microgrids. For the inner loop of the grid-connected converter, a voltage modulated direct power control is employed to obtain two second-order linear time-invariant systems, which guarantees that the closed-loop system is globally exponentially stable. For the outer loop, a sliding mode control strategy with a load current sensor is employed to maintain a constant dc-link voltage even in the presence of constant power loads at the dc-side, which adversely affect the system stability. Furthermore, an observer for the dc-link current is designed to remove the dc current sensor at the same time improving the reliability and decreasing the cost. From both simulation and experimental results obtained from a 15-kVA prototype setup, the proposed method is demonstrated to improve the transient performance of the system and has robustness properties to handle parameter mismatches compared with the input-output linearization method.

Model Predictive Power Control for Bidirectional Series-Resonant Isolated DC–DC Converters With Fast Dynamic Response in Locomotive Traction System

High-frequency bidirectional dual-bridge series-resonant dc–dc converters have been attracted more attention in power electronic transformer (PET) due to high power density and efficiency. In this article, a model predictive power control method with phase shift modulation is proposed, to improve the dynamic response and robustness of the converter without load current sensor. In addition, the proposed method is insensitive to the resonant parameters in the adopted converter and can keep excellent dynamic characteristics even if the resonant parameter deviates from the desired operating point, which indicates good robustness. Effectiveness of the proposed control is verified on a 400-W scale-down experimental prototype with resistance load and inverter load, respectively. Compared with traditional voltage loop control and model predictive voltage control schemes, the proposed scheme can achieve a faster dynamic response of the output voltage in load and input voltage step change.

Robust Current Sensorless Control of VSC-Based MTDC Transmissions for Integrating Wind Farms

This article presents an observer-based robust current sensorless control (RCSC) scheme for voltage-source-converter (VSC)-based multiterminal direct-current (MTDC) transmission system integrated with wind farms. Perturbation observer-based point of common coupling (PCC) voltage controller and dc-link voltage controller are designed for wind farm station (WFS) and grid-side station (GSS) of MTDC, respectively, for grid integration of multiple wind farms. Perturbation states are defined to describe the interactions of voltage control loops of nonlinear VSC model, and the feedback linearization control is realized based on the state estimations provided by perturbation observers to achieve the decoupled voltage control of MTDC. Neither current sensors nor parameters of MTDC are required in the RCSC scheme, thus achieving the robust sensor fault-tolerant operation of the MTDC system. Simulation and experimental studies are undertaken on a three-terminal MTDC transmission system integrated with two wind farms to verify the control performance of the RCSC scheme under the conditions of wind speed variations, sudden load changes, parameter variations, and current sensor faults.

A 7.4-MHz Tri-Mode DC-DC Buck Converter With Load Current Prediction Scheme and Seamless Mode Transition for IoT Applications

The growth of IoT applications requires DC-DC converters to have small printed circuit board (PCB) areas and high efficiency over a wide load range. A multi-mode operation of DC-DC converters, therefore, is often necessary to achieve this high efficiency over a wide load range. This paper introduces a tri-mode DC-DC buck converter for IoT applications. The tri-mode operation with PWM, PFM, and multiple-sawtooth PWM (MSPWM) modes helps to retain the high efficiency over the wide load range. The MSPWM mode also enhances a noise margin of the converter, ensuring a regular switching operation at an ultra-light load condition. With a load current prediction scheme, the proposed tri-mode converter requires neither additional load current sensor nor multiple mode controllers. In addition, a soft-start operation is employed to prevent an in-rush current. The proposed tri-mode buck converter has been fabricated through a 0.18- $\mu \text{m}$ CMOS process with a chip area of 0.97 mm $\times0.88$ mm. A load-dependent seamless mode transition is realized, and a maximum converter efficiency of 91% has been measured with a 7.4-MHz switching frequency.

Modeling and Control of a DC Motor Coupled to a Non-Rigid Joint

Throughout this paper, the model, its parameter estimation and a controller for a solution using a DC motor with a gearbox worm, coupled to a non-rigid joint, will be presented. First, the modeling of a non-linear system based on a DC Motor with Worm Gearbox coupled to a non-rigid joint is presented. The full system was modeled based on the modeling of two sub-systems that compose it—a non-rigid joint configuration and the DC motor with the worm gearbox configuration. Despite the subsystems are interdependent, its modelling can be performed independently trough a carefully chosen set of experiments. Modeling accurately the system is crucial in order to simulate and know the expected performance. The estimation process and the proposed experimental setup are presented. This setup collects data from an absolute encoder, a load cell, voltage and current sensors. The data obtained from these sensors is presented and used to obtaining some physical parameters from both systems. Finally, through an optimization process, the remaining parameters are estimated, thus obtaining a realistic model of the complete system. Finally, the controller setup is presented and the results obtained are also presented.

Delta-Sigma Modulation Based Common-Mode Voltage Elimination in Direct Matrix Converter

The direct matrix converter (DMC) offers a compact and robust solution over typical ac–dc–ac converter, by enabling direct ac–ac power conversion without any energy storage requirements. Moreover, it offers enhanced source current quality, innate bidirectionality and power factor correction capabilities. Its industrial suitability is further advocated by the elimination of common-mode voltage through the DMC topology. Space vector modulation and model predictive control based approach to common-mode voltage elimination in matrix converter, are previously proposed. This article proposes the delta-sigma modulation for common-mode voltage elimination in matrix converter, which is computationally less cumbersome and performs better as compared to previously documented methods. This method utilizes only six most optimum states of DMC that yield zero common-mode voltage, and performs load voltage and source current control by computing each error variable (delta), integrating it (sigma) and further minimizing it within a hysteresis band. Source current control necessitates load current estimation, which is done through predictive model of the load, hence eliminating load current sensors.

Real-Time Implementation of Shunt Active Power Filter With Reduced Sensors

Performance of shunt active power filter (SAPF) depends on the effectiveness of control strategy, which requires information about voltages and currents obtained from sensors. Faults in these sensors cause SAPF to aggravate power quality problems instead of compensating it. Therefore, sensorless control of SAPF is a very attractive solution for its robust operation. This article proposes an Adaline-based control strategy that requires only source currents and dc voltage measurement, thus reducing source voltage and load current sensors. The proposed estimation techniques enable SAPF to work under highly dynamic load conditions where other similar approaches with reduced sensors cease to perform. A comparative analysis with the classical approach (using all sensors) under the same load conditions is done to show the effectiveness of the proposed techniques. The proposed control strategy is first simulated on MATLAB/Simulink platform and further verified on the OPAL-RT 5700 hardware-in-loop FPGA-based real-time platform.

Observer-based load current sensorless control strategy of inverter circuit in three-phase UPS

A load current sensorless control strategy using an optimized observer is designed for a three-phase online transformer-based UPS. A closed-loop observer containing state feedback is constructed based on the improved state space model of the inverter circuit. A simple feedback matrix design method is then applied to the observer according to the dead-beat control law, and the load current feedforward control scheme is reconstructed using the proposed observer. This control strategy can save three load current sensors, reduce the THD of the output voltage, and improve dynamic performance. The effectiveness of this strategy is verified by conducting simulation and experiment in a 10 kVA UPS.

Predictive Delta Sigma Modulation for Three-Phase to Three-Phase Matrix Converters

As research in matrix converters (MCs) has progressed over time, space vector modulation has emerged as the most popular technique for their modulation. Lately, model predictive control (MPC) has also been explored for the modulation and control of MCs, primarily gaining popularity due to the ease in realization of multiple objectives, as desired in MCs. However, multi-objective MPC employs assignment of weights to each control objective, wherein weight tuning is either empirical in nature or computationally cumbersome. This paper proposes a new modulation technique for MCs, inspired from delta sigma modulation for voltage source converters, that can be used for load voltage and source current control of MCs. Since source currents are samples of the load current envelope, it is required that this envelope be known for the control of source current. To eliminate load current sensors, predictive model of the load is used in envelope estimation. Further, independent switching schemes are generated for each objective, and an error minimization approach is used in integrating the two schemes into a final state selection, hence eliminating weighing factors. Unlike MPC, error predictions for all states of MCs, are not needed, hence facilitating easier implementation without significant processor burden, besides ensuring the quality of response.

Extended State Observer Based Flatness Control for Fuel Cell Output Series Interleaved Boost Converter

Output series interleaved boost converter (OS-IBC) has become a promising candidate for fuel cell application, due to the features of high voltage gain and low input current ripple. To achieve a satisfactory control performance for the OS-IBC, a robust dual loop control strategy is designed in this article. The designed controller comprises an inner loop dedicated to inductor current tracking and an outer loop aimed at output voltage regulation, both of which are based on flatness control. Furthermore, the extended state observers (ESO) are integrated into this control algorithm for online estimating the uncertain input voltage and output current of the equivalent converter. With this ESO, the parasitic circuit parameters are considered into the estimations, and meanwhile, the input source voltage sensor and load current sensor can be omitted. The feasibility and robustness of the designed controller have been successfully validated by simulation and experimental results obtained using a 240-W prototype converter and a dSPACE control platform.

A control scheme for voltage unbalance compensation in an islanded microgrid

One of the major power quality issues in low-voltage (LV) microgrids is the voltage unbalance which has adverse effects on electrical devices. This paper presents a novel control scheme to mitigate the voltage unbalance by a photovoltaic (PV) system. In this study, load current sensors are eliminated and the PV system mitigates the voltage unbalance by analyzing its terminal voltage. This could effectively reduce the cost and complexity of compensation system because of the difficulties of load current sensors. The proposed control strategy is developed for a three-phase PV. As the inverter detects the voltage unbalance at its terminal, the proposed control algorithm calculates the compensation reference currents based on the double synchronous reference frame (DSRF) analysis of the PV terminal voltage. Therefore, the PV inverter injects the compensating currents to the microgrid. The effectiveness of the control scheme is verified by simulation studies in the PSCAD/EMTDC environment.