Robert Griñó

Digital Repetitive Control of a Three-Phase Four-Wire Shunt Active Filter

Shunt active power filters have been proved as useful elements to correct distorted currents caused by nonlinear loads in power distribution systems. This paper presents an all-digital approach based on a particular repetitive control technique for their control. Specifically, a digital repetitive plug-in controller for odd-harmonic discrete-time periodic references and disturbances is used for the current control loops of the active filter. This approach does not introduce a high gain at those frequencies for which it is not needed and, thus, improves robustness of the controlled system. The active power balance of the whole system is assured by an outer control loop, which is designed from an energy-balancing perspective. The design is performed for a three-phase four-wire shunt active filter with a full-bridge boost topology. Several experimental results are also presented to show the good behavior of the closed-loop system

Technical Communique: Digital repetitive plug-in controller for odd-harmonic periodic references and disturbances

This work develops a digital repetitive plug-in controller for odd-harmonic discrete-time periodic references and disturbances. The controller presents a novel structure and it has a lower data memory occupation than the usual repetitive controllers because it takes advantage of the particular characteristics of the signals to track or attenuate. A sufficient criterion of stability, several hints for its practical application and an example are also included in the work.

Power-Quality Improvement of a Stand-Alone Induction Generator Using a STATCOM With Battery Energy Storage System

This paper presents a STATCOM with a self-oscillating bidirectional dc-dc converter for interfacing battery energy storage in a stand-alone induction generator system. The self-oscillation mode is based on relay feedback control with hysteresis. To reduce the output current ripple, an LCL filter is connected between the half bridge of this dc-dc converter and the energy storage system. The other side of bidirectional converter is coupled with a voltage-source converter. The proposed control allows that the previous electronic converters, with an additional resistive dump load, compensate all disturbances in a self-excited induction generator due to three-phase four-wire loads and an improvement of system efficiency. The simulated results show good performance of the stand-alone power system under different loading conditions.

Demonstration of the internal model principle by digital repetitive control of an educational laboratory plant

A key topic in classical control theory is the Internal Model Principle (IMP). A particular case of the IMP for tracking periodic references or attenuating periodic disturbances in closed-loop control systems is a technique called repetitive control. This work proposes and describes an educational laboratory plant to show the students the advantages of repetitive controllers in systems with periodic references or disturbances. The plant has been designed to be low cost, easy to build, and subject to periodic disturbances with a clear physical explanation. More specifically, it consists of a pulsewidth modulation (PWM) electronic amplifier, a small dc motor, and a magnetic setup that generates a periodic load torque under constant mechanical speed operation. The control objective for the closed-loop control system is to regulate the mechanical speed to a constant value in spite of the periodic load torque disturbance. In order to accomplish this performance specification, a detailed design of a digital repetitive controller is presented, and some basic experimental results are provided to prove its good behavior. The paper also includes some repetitive control concepts and facts that teaching experience shows as essential to understand the design process.

Robust controller for a full-bridge rectifier using the IDA approach and GSSA modeling

An interconnection-and-damping assignment passivity-based control (IDA-PBC) for a full-bridge rectifier is presented in this paper. The closed-loop system performance fulfils unity power factor in the ac mains and output dc voltage regulation. The controller design takes advantage of the generalized state space averaging (GSSA) modeling technique to convert the quoted nonstandard problem (in actual variables) into a standard regulation one (in GSSA variables). In this approach, the output current is the measured signal instead of the line current; therefore, the number of sensors does not increase in comparison with traditional approaches. The whole system is robust with respect to load variations.

Nonlinear system identification using additive dynamic neural networks-two on-line approaches

This paper proposes a class of additive dynamic connectionist (ADC) models for identification of unknown dynamic systems. These models work in continuous time and are linear in their parameters. Also, for this kind of model two on-line learning or parameter adaptation algorithms are developed: one based on gradient techniques and sensitivity analysis of the model output trajectories versus the model parameters and the other based on variational calculus, that lead to an off-line solution and an invariant imbedding technique that converts the off-line solution to an on-line one. These learning methods are developed using matrix calculus techniques in order to implement them in an automatic manner with the help of a symbolic manipulation package. The good behavior of the class of identification models and the two learning methods is tested on two simulated plants and a data set from a real plant and compared, in this case, with a feedforward static (FFS) identifier.

Design, Construction, and Control of a Stand-Alone Energy-Conditioning System for PEM-Type Fuel Cells

This paper presents the development of an energy-conditioning system for a proton exchange membrane (PEM) type fuel cell (FC). The developed system provides 230 V ac rms at 50 Hz, with a nominal output power of 1 kVA, and is able to handle sporadic high-power demands up to 5 kVA. An auxiliary power unit (APU), using a bank of supercapacitors as energy-storing device, provides this extra power during a certain amount of time. The output current ripple and step response constraints of the FC unit are considered in the design. A frequency-decoupling scheme is used, in which the FC provides only the low-frequency requirements, while the fast/high-frequency demands are supplied by the APU. A detailed description is given for its different constructive modules, their control design, and implementation.

Conditions for Existence of Equilibria of Systems With Constant Power Loads

In this paper we investigate the sine qua non condition of existence of equilibria for electrical systems with external (AC or DC) sources furnishing constant power to the loads, which is a scenario encountered in modern applications. Two general cases are considered, when the system is i) linear time-invariant or ii) nonlinear, with dynamic behavior described by a port-Hamiltonian model with constant dissipation and switching interconnection matrix. The latter class includes the practically important case of power converters. For both cases necessary and sufficient conditions for existence of equilibria are given, which give an upper bound on the power dissipated in steady-state that should exceed the extracted constant power. The existence of the equilibrium is ensured if and only if the inequality is satisfied.

High-Performance Control of a Single-Phase Shunt Active Filter

Shunt active power filters are devices, connected in parallel with nonlinear and reactive loads, which are in charge of compensating these characteristics in order to assure the quality of the distribution network. This paper analyzes the dynamics of a dc bus split-capacitor boost converter used as an active filter and proposes a control system which guarantees the desired closed-loop performance (unity power factor and load-current harmonics and reactive-power compensation). The proposed controller is hierarchically decomposed into two control loops, one in charge of shaping the network current and the other in charge of assuring the power balance. Unlike previous works that appeared in the literature, both control loops are analytically tuned. This paper describes the analytical design of the controller and presents some experimental results that show the good performance of the closed-loop system.

Standalone Self-Excited Induction Generator with a Three-Phase Four-Wire Active Filter and Energy Storage System

This paper proposes a system, based on a self- excited induction generator with a shunt electronic converter, to feed isolated three-phase and single-phase linear or nonlinear loads. The electronic converter is composed by a three-phase four-wire voltage source inverter (VSI) and, connected to its dc side, two dc/dc converters. The VSI compensates the current harmonics, the reactive power and the load unbalances. The first of the dc/dc converters is a battery charger/discharger and the other converter dissipates the active power excess, through a chopper, so these dc/dc converters keep the active power balance of the complete system. The designed control architecture assures that, in steady state, the rms values of the voltages and the frequency remain at the their reference values. The simulated results show a good performance of the system under different loading conditions.