Internal Control Loop Research Articles

A Passivity-Based Stability Analysis of the Active Damping Technique in the Offshore Wind Farm Applications

The LCL -based filter has been widely applied to mitigate the size of the inductor in the high-power converter, but it usually leads to resonance in the system. Therefore, an active damping technique based on the virtual resistor is provided in this paper for the LCL -filter system. The literature papers only suppressed the resonance of the LCL -filter and focused on the stability of the internal current control loop with an inductive grid impedance. Therefore, these previous stability analysis methods cannot be suitable for offshore wind farm applications due to the multiple resonance frequency characteristic of the transmission cable and multiparalleled converters. Therefore, this paper analyzes the control stability with both of the internal resonance ( LCL -filter) and external resonance (between the grid impedance and current controller). Besides, the behavior of multiparalleled converter and the multiple resonance frequency of long transmission cable are discussed and analyzed for the offshore wind farm applications. Finally, the laboratory and simulation results are for the proposed method verification.

Modelling and Control Design for Energy Management of Grid Connected Hybrid PV-wind System

<p class="MsoNormal" style="margin-right: -14.15pt; text-align: justify; text-justify: inter-ideograph;">This paper deals with the control of hybrid PV-WIND power conversion structure. This paper develops a very important contribution which is the use of a single DC to DC converter, linearization of control of the three- level boost converter (TLBC) considering the imperfections of the passive components. The (TLBC) control provides balancing of capacitor voltages and maximum power operation of PV generator. For reasons of simplicity, a linearization based on the dynamic compensation of the disturbance is proposed. A sensorless maximum power point tracking (MPPT) algorithm is used to maximize a power extracted of the wind generator. The proportional relation between the rotational speed and the output voltage of the rectifier allows to use a voltage sensor to estimate the DC bus voltage reference instead of a mechanical speed sensor. The control of the three-phase inverter allows a transfer of the active power, the power factor close to the unit and thus a limitation of the reactive power injected into the grid. The external control loop performs the regulation of the common DC bus voltage while the internal control loop regulates the dq components of the currents injected into the grid. The simulation results showed the validity of the control approach. The proposed power conversion structure based on a single static converter has shown very good performance in terms of efficiency, the quality of the energy produced, complementarity between the two renewable sources and reliability. The paper ends with conclusions.</p>

Real-time implementation of three-level inverter-based D-STATCOM using neuro-fuzzy controller

A distribution static compensator (D-STATCOM) is a custom power device connected in parallel to a power system to address electric power quality problems caused by reactive power and harmonics. To obtain high performance from a D-STATCOM, the D-STATCOM's \textit{dq}-axis currents must be controlled in an internal control loop. However, control of the D-STATCOM's currents is difficult because of its nonlinear structure, cross-coupling effect between the \textit{d}- and \textit{q}-axis, undefined dynamics, and fast changing load. Therefore, the controller to be preferred for a D-STATCOM should have a nonlinear and robust structure. In this study, a neuro-fuzzy controller (NFC), which is a robust and nonlinear controller, is proposed for \textit{dq}-axis current control of a D-STATCOM. A DSP-based experimental setup is built for real-time control. The basic building block of the experimental setup is a three-level cascaded inverter. This inverter is constructed by using three IPM intelligent modules. A DS1103 controller card is used for real-time control of the D-STATCOM's experimental setup. The control algorithm is prepared in MATLAB/Simulink software and loaded to the DS1103 controller card. The performance of the NFC current-controlled D-STATCOM is tested for different load conditions: no load to full inductive, no load to full capacitive, full inductive to full capacitive, and full capacitive to full inductive. For this aim, the reactive current setpoint is changed as a step. The experimental results are presented to show the efficiency of the proposed controller under different load conditions.

Diesel air path control using pressure difference: Pumping loss and aging considerations

Pressure difference across the exhaust and intake manifolds ([Formula: see text] P) is a crucial variable to control the pumping loss and cylinder charge dilution through the exhaust gas recirculation in a diesel engine. This paper presents a novel architecture for controlling [Formula: see text] P and the engine-out NO x emissions, which increases the controller tolerance to engine components aging. The architecture has an internal control loop, designed as a two-input two-output controller, to coordinate the exhaust gas recirculation and variable geometry turbine valves. Using feedback from [Formula: see text] P and the estimated cylinder oxygen ratio [Formula: see text] cyl, the two-input two-output controller regulates the pumping loss and the engine NO x emissions. To reduce high turbo lag and its associated slow air–fuel ratio ([Formula: see text]) response, which are inherent features of a [Formula: see text] P-based control strategy, the two-input two-output linear quadratic controller is tuned such that [Formula: see text] is also regulated, but only during fast transients. An external loop is supplementing the core two-input two-output controller correcting the internal loop set points to reduce the effects of [Formula: see text] cyl estimation errors on NO x control and ensure [Formula: see text] stays above a minimum value, [Formula: see text] min, critical for smoke emissions. As a feature of the proposed control system, direct feedback from [Formula: see text] P increases pumping loss robustness to common degradation in diesel engines, namely, turbine efficiency and diesel particulate filter blockage due to ash deposit, compared to a conventional boost pressure–based controller. Also, it is shown that the input–output coupling structure of the proposed two-input two-output controller and use of the NO x feedback mitigate effects of exhaust gas recirculation fouling and associated exhaust gas recirculation valve saturation on increase in NO x emission.

Cargador de baterías fotovoltaico con control por modos deslizantes y limitación de la derivada de corriente de carga

En los sistemas fotovoltaicos (PV) aislados, los cargadores de baterías son importantespara garantizar el suministro de energía cuando la luz solar no está disponible. Dichoscargadores necesitan realizar el seguimiento del punto de máxima potencia (MPPT) ylimitar la derivada de corriente de carga de las baterías para extender su vida útil. Esteartículo propone un sistema cargador de baterías compuesto por un convertidor Buck, uncontrol en cascada de la corriente de las baterías y la tensión del panel PV, y la técnica deMPPT Perturbar y Observar (P&O). El P&O genera la referencia de tensión del panel parael lazo externo del control en cascada, implementado con un regulador P, cuya acción decontrol es la referencia de la corriente de carga de las baterías. Dicha referencia de corrientepasa por un limitador de derivada antes de llegar al lazo interno de control de corriente delas baterías, el cual es implementado con un control por modos deslizantes (SMC). Elartículo incluye el análisis de transversalidad y alcanzabilidad del SMC, así como elprocedimiento de diseño del regulador P. El sistema propuesto se valida por medio desimulaciones en el software PSIM mostrando la capacidad de realizar el MPPT y limitar laderivada de corriente de carga de las baterías al mismo tiempo.

A reconfigurable and instantaneous triple RF bands energy harvester using internal control loop

This paper presents an autonomous energy harvester able to perform a high radio frequency (RF) power tracking to achieve a DC renewable power source. The proposed simultaneous triple RF band energy harvesting system has the potential of being deployed along with remote sensor nodes to enhance their operational life-times. Two multi-stages rectifiers harvest the RF energy from three bands: 900 MHz, 1.2 and 2.4 GHz are proposed. A control loop is implemented to reconfigure the operating frequency of the rectifier based on the amount of available input power. The harvester is designed using TSMC 65-nm CMOS technology and tunable matching network to vary the input impedance of the main rectifier between 900 MHz and 1.2 GHz and the second rectifier harvests from 2.4 GHz. The results show a peak efficiency of 57, 43 and 33% at 2.4 GHz, 900 MHz and 1.2 GHz respectively.

Control and power sharing among parallel three‐phase three‐wire and three‐phase four‐wire inverters in the presence of unbalanced and harmonic loads

In this paper, the parallel operation of a three‐phase three‐wire inverter and a three‐phase four‐wire inverter in the presence of unbalanced and nonlinear loads is investigated. The proposed control method has two current internal and voltage external control loops. The current internal loop has a proportional‐resonant controller. The voltage external loop has two parts, including voltage controller and load current sharing. In the current sharing part, first, the output of the voltage controller is broken to a harmonic and is shared then between the inverters through the new strategy: (i) supply of harmonic components of load current by four‐leg inverter and sharing fundamental component of load current evenly between the inverters and (ii) supply of zero‐sequence load current by four‐leg inverter and sharing of the rest of components evenly between two inverters. The proposed system is capable of feeding balanced, unbalanced and nonlinear loads and provides the proper sinusoidal voltage at both ends of the loads by exact sharing of power between parallel inverters. The simulation results show the proper functioning of the proposed system. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Multi-Resonant based Output Voltage Control of Autonomous Distributed Generators

The distributed or decentralized generation electricity constitutes the central stone of various recent energy models, such as the intelligent electrical supply networks. The quality of energy in this type of structure depends primarily on the strategy of control adopted, in order to guarantee proper operation according to the international standards. The strategy of control proposed in this paper uses two control loops. An internal control loop aims at deadening the phenomena of resonance while ensuring the required control dynamic for fast disturbance rejection. As for the external control loop, a multi-resonant composed of a stabilizing state feedback that ensure an asymptotic tracking of the voltage reference with a weak rate of harmonic distortion. Finally, experimental results are presented to show the performances and feasibility of the proposed control strategy.

DFIG performance improvement in grid connected mode by using fractional order [PI] controller

This article has focused on designing and applying the fractional order [PI] (FO[PI]) controllers in the rotor side converter (RSC) of a doubly-fed induction generator (DFIG) wind turbine in the wind farm connected to a weak grid. To design the controllers, an analytical approach is developed to ensure the frequency domain specifications. The proposed fractional order controllers are simultaneously applied in the internal and external control loops of the RSC to improve DFIG active power, rotor speed and rotor current profiles by occurring various balanced and unbalanced transient faults. Different simulation results are obtained to verify the efficacy of the proposed method at both middle and high mean wind speeds. Meanwhile, the uncertainty in the grid parameters including the short circuit capacity (SCC) and X/R ratio is surveyed by reducing these parameters to show the superior performance of FO[PI] controllers in comparison with PI ones.

Direct digital design of a sliding mode‐based control of a PWM synchronous buck converter

A discrete-time sliding mode approach allowing direct digital design of a pulse width modulation (PWM) control of a synchronous buck converter is presented in this study. Without the need of a compensating ramp, a non-linear difference equation representing the output voltage dynamic behaviour is employed to demonstrate the global stability of the internal control loop of the inductor current. Discrete-time small-signal model is derived from the linearisation of the ideal sliding-mode equations, which facilitates the design of the output voltage controller. This model exhibits a zero whose value depends on the operating point coordinates and explains the duty cycle delay associated to digitally PWM controlled converters. The validity of the transfer function is demonstrated through simulation by comparing its frequency behaviour with that obtained from the more accurate switched model of the converter. Experimental results for start-up, load and line perturbations, current and voltage reference variations in a 25 W prototype switching at 100 kHz are in good agreement with the theoretical predictions.

Impedance Control for Robotic Rehabilitation: A Robust Markovian Approach.

The human-robot interaction has played an important role in rehabilitation robotics and impedance control has been used in the regulation of interaction forces between the robot actuator and human limbs. Series elastic actuators (SEAs) have been an efficient solution in the design of this kind of robotic application. Standard implementations of impedance control with SEAs require an internal force control loop for guaranteeing the desired impedance output. However, nonlinearities and uncertainties hamper such a guarantee of an accurate force level in this human-robot interaction. This paper addresses the dependence of the impedance control performance on the force control and proposes a control approach that improves the force control robustness. A unified model of the human-robot system that considers the ankle impedance by a second-order dynamics subject to uncertainties in the stiffness, damping, and inertia parameters has been developed. Fixed, resistive, and passive operation modes of the robotics system were defined, where transition probabilities among the modes were modeled through a Markov chain. A robust regulator for Markovian jump linear systems was used in the design of the force control. Experimental results show the approach improves the impedance control performance. For comparison purposes, a standard force controller based on the fixed operation mode has also been designed. The Markovian control approach outperformed the control when all operation modes were taken into account.

Nonlinear modeling and simulation of battery energy storage systems incorporating multiband stabilizers tuned by Meta-heuristic algorithm

A new control strategy including multiband stabilizers is designed for battery energy storage system (BESS). The introduced control scheme includes two internal control loops equipped with internal proportional-integral (PI) type controllers for active and reactive power control. These control loops are also equipped with multiband stabilizers. All controllers (i.e., internal controllers and multiband stabilizers) are simultaneously tuned by Meta-heuristic optimization techniques. Several disturbances are applied and simulated. The viability and effectiveness of the introduced method is verified through various nonlinear simulations and comparative studies.

MPC for Robot Manipulators With Integral Sliding Modes Generation

This paper deals with the design of a robust hierarchical multiloop control scheme to solve motion control problems for robot manipulators. The key elements of the proposed control approach are the inverse dynamics-based feedback linearized robotic multi-input-multi-output (MIMO) system and the combination of a model predictive control (MPC) module with an integral sliding mode (ISM) controller. The ISM internal control loop has the role to compensate the matched uncertainties due to unmodeled dynamics, which are not rejected by the inverse dynamics approach. The external loop is closed relying on the MPC, which guarantees an optimal evolution of the controlled system while fulfiling state and input constraints. The motivation for using ISM, apart from its property of providing robustness to the scheme with respect to a wide class of uncertainties, is also given by its capability of enforcing sliding modes of the controlled system since the initial time instant, allowing one to solve the MPC optimization problem relying on a set of linearized decoupled single-input-single-output (SISO) systems that are not affected by uncertain terms. The proposal has been verified and validated in simulation, relying on a model of a COMAU Smart3-S2 industrial robot manipulator, identified on the basis of real data.

Performance evaluation of an improved model predictive control with field oriented control as a benchmark

Compared to the widespread modulation-based control strategies such as field oriented control (FOC), MPC eliminates the use of internal current control loops and modulation block, hence featuring very quick dynamic response. Furthermore, MPC well respects the discrete nature of power converters by evaluating the influence of each voltage vector on the concerned control variables, which are usually combined into a cost function, hence featuring simple concept. In spite of the merits of quick response and conceptual simplicity, it seems that MPC may be inferior to FOC in terms of steady-state performance, especially in the low speed range, which is usually a drawback of MPC-branched methods. This study proposes an improved two-vectors-based MPC (MPC2) and compares it to the well-established FOC. A detailed experimental study of both methods is presented, including steady-state performance, dynamic response, low speed operation and control complexity. Very promising results are obtained in MPC2 by providing better steady-state performance and much quicker response than FOC under the condition of similar average switching frequency. The results prove that MPC2 is a powerful alternative to FOC and may find wide applications in the near future.

Electrostimulated machining of metals

New mechanical equipment requires structural materials whose high performance cannot be ensured by traditional methods. A promising approach to the shaping of steel is the use of powerful unipolar current pulses with the following characteristics: amplitude 10–15 kA; pulse frequency up to 400 Hz; pulse length up to 100 μs. The widespread industrial use of this technique is hindered by the low efficiency of the corresponding pulse generators, which also draw considerable power from the ac grid and are not sufficiently controllable. In the present work, a generator of powerful unipolar current pulses that is free of those defects is described. It includes a charging system connected to power capacitors; and a thyristor switch that discharges the capacitors to a low-resistance load. To reduce the power drawn from the grid, the generator includes a recharging device based on a thyristor, which is connected to a reverse-parallel thyristor switch. To permit regulation of the pulse amplitude and increase its power, the uncontrollable dc source in the charging system is replaced by two irreversible thyristor converters in series. That permits control of the voltage at the power capacitors. To optimize capacitor charging, a two-loop subordinate control system regulates the parameters of the pulse generator: the external control loop governs the voltage charging the capacitors, while the internal control loop governs the charging current. MATLAB Simulink software is used to create a model of the proposed generator. The model corresponds to the actual pulse generator used at Siberian State Industrial University to investigate the electrostimulated plastic deformation of metals and alloys. The model permits improvement in the characteristics of the pulse generator and its operating conditions. A benefit of the proposed generator over its counterparts is that the power drawn from the grid is considerably reduced, while the voltage charging the capacitor may be regulated in the range up to 600 V, with pulse frequencies up to 400 Hz. The generator may be used industrially—in particular, in rolling mills when drawing steel wire that is hard to deform.

Influence of the Location of the Internal Temperature Control Loop on the Performance of the Dual Temperature Control for Feed Temperature Disturbance

Influence of the Location of the Internal Temperature Control Loop on the Performance of the Dual Temperature Control for Feed Temperature Disturbance

Application of neural models as controllers in mobile robot velocity control loop

Abstract This paper presents the application of an inverse neural models used as controllers in comparison to classical PI controllers for velocity tracking control task used in two-wheel, differentially driven mobile robot. The PI controller synthesis is based on linear approximation of actuators with equivalent load. In order to obtain relevant datasets for training of feed-forward multi-layer perceptron based neural network used as neural model, the mathematical model of mobile robot, that combines its kinematic and dynamic properties such as chassis dimensions, center of gravity offset, friction and actuator parameters is used. Neural models are trained off-line to act as an inverse dynamics of DC motors with particular load using data collected in simulation experiment for motor input voltage step changes within bounded operating area. The performances of PI controllers versus inverse neural models in mobile robot internal velocity control loops are demonstrated and compared in simulation experiment of navigation control task for line segment motion in plane.

Modeling and Control of the CSCEC Multi-Function Testing System

In order to promote the research and development on evaluating the seismic performance of structures, China State Construction Engineering Corporation (CSCEC) planned to construct a large-scale loading testing facility, the Multi-Function Testing System (MFTS). This facility can perform full-scale, real-time, 6-degree-of-freedom static and dynamic testing of rubber bearings and many types of structural components including long columns, shear walls and cross shape joints. The basic performances of the MFTS are a clearance of 9.1 m × 6.6 m × 10 m for specimen installation, maximum x-directional displacement 1500 mm, maximum y-directional velocity 1570 mm/s and maximum z-directional compressive load 108 MN. The system configuration and performance specifications of the MFTS are presented in this paper. The inverse kinematics model and the nonlinear model of the hydraulic servosystem of the MFTS are built. A modified feedback forward kinematics algorithm is developed for real-time control of the MFTS. Internal force characteristics of the loading system are analyzed. The internal force control method based on real-time solution of basis of internal force space is proposed for the system with large motion ranges. The motion controller combining position control loop and internal force control loop is developed. To meet the requirement of simultaneously imposing vertical compressive load and horizontal displacement, a mixed load and displacement controller is designed, where a direct force control loop is used to improve the response speed of the force control and reduce spatial dynamic coupling effects. Finally, a dynamic bearing testing is performed. The test results demonstrate that the system using the proposed controller has good abilities on position tracking, force balance, and load following.

Control of cable-driven manipulators in the presence of friction

Cable-driven systems are of great interest in applications for which remote actuation is required, like for instance to operate within medical imaging devices. In such applications, robotic architectures based on remotely actuated cable-driven manipulators (CDM) offer innovative design options. However, unlike more conventional CDM, such designs involve specific control problems. This paper deals with the control of CDM in the presence of friction, as experienced when particular design constraints have to be taken into account (size, materials, length of transmissions). In this case, the influence of friction on the manipulator motions is such that dynamic modeling, identification and control, are no longer adapted, nor even possible. As a result, for quasi-static positioning tasks, we propose a CDM position control strategy resulting from a cascade structure, with an internal cable tension control loop to handle friction. Cable tension is measured using an original instrumented compliant structure. From the control point of view, the originality of the present paper comes in particular from the development of a feasibility algorithm which allows us to limit cables tensions within a specified range. This strategy is experimentally assessed on a robot for image-guided medical procedures.

Multi-parameter bifurcation analysis of subsynchronous interactions in DFIG-based wind farms

This work analyzes the dynamics involved in subsynchronous interactions between wind farms and series-compensated transmission lines. This adverse phenomenon may arise when doubly-fed induction generators are radially connected to an ac transmission line with series capacitive compensation. The resulting subsynchronous oscillations can produce the system instability and cause a severe damage to the wind turbines. The study is carried out combining tools from bifurcation theory, eigenvalue analysis and nonlinear time-domain simulations. The impact on the subsynchronous mode due to the variation of a set of key parameters is considered. These parameters include the series compensation of the transmission line, the wind speed (generated power), the wind energy penetration level, and a gain of the internal control loop of the wind turbine. The bifurcation study determines that the underlying mechanism associated with the appearance of subsynchronous oscillations can be explained by means of Hopf bifurcations of the equilibrium point and their corresponding limit cycles. In addition, the saturation of the wind turbine converters plays an important role in the dynamics, introducing non-smooth bifurcations that are also analyzed.