C. Nunez

Robust sigma–delta generalised proportional integral observer based control of a ‘buck’ converter with uncertain loads

This article describes the design of an observer based robust linear output feedback controller for the regulation and output reference trajectory tracking tasks in switched ‘buck’ converter circuits feeding a completely unknown time-varying load. The state-dependent perturbation effects of the unknown load resistance are on-line estimated by means of a generalised proportional integral (GPI) observer, which represents the dual counterpart of GPI controllers introduced in Fliess, Márquez, Delaleau and Sira-Ramírez (Fliess, M., Márquez, R., Delaleau, E., and Sira-Ramírez, H. (2002), ‘Correcteurs Proportionnels-intégraux Géneralisés’, ESAIM: Control, Optimisation and Calculus of Variations, 7, 23–41). The reconstructed perturbation complements the controller in a cancellation effort which allows the core of the feedback controller to become a traditional proportional derivative (PD) controller. The designed average feedback controller is then implemented via a sigma–delta-modulator, which effectively translates the designed continuous average feedback control input signal into a discrete valued switched input signal driving the converters input switch and preserving all relevant features of the average design. The Appendix collects some generalities about GPI observers.

Single-Phase AC-AC Converter Operating as a Dynamic Voltage Restorer (DVR)

This paper presents a single-phase AC-AC matrix converter which is able to compensate voltage harmonics and voltage regulation at critical loads terminals. The converter is composed with the minimum number of switching devices and is controlled using a non-linear law based on passivity achieving a high reliability and robustness during transient and steady state operation condition. The proposed scheme has the advantage that energy storage devices are not required. The converter is connected between the AC mains and the load through a series transformer. A DSP and a FPGA are used to program the passivity-based controller and to determine the state of the switches respectively. In this case, the converter is able to compensate up to 25% voltage sags and 50% voltage swells and to eliminate up to the fifteenth harmonic component. The tested system presents a fast time response and the stabilization time of the load voltage is less than 1 ms. Analysis and modeling as well as simulation and experimental results of a 5 kVA, 127 V, 60 Hz experimental setup are analyzed and presented

Voltage disturbances and unbalance compensation by the use of a 3-phase series active filter

The quality of the AC mains and the power transferred from it can be improved by the use of electronic power systems such as active filters. Line perturbations (voltage changes, noise, sags, dips, flicker, harmonics, etc.) can be reduced by the action of a voltage conditioner or a series active filter. This paper is related to the study of a three-phase active filter topology that improves the voltage quality and is capable of working with two phases if any one of the 3 phases is faulted. Energy storage is achieved by a set of capacitors that compensate voltage unbalances among phases within a certain range, without the need of an additional energy source. Furthermore, the present paper presents a compensation method that is programmed in a DSP-based board. Finally, simulation and experimental results are shown.

Analysis and evaluation of control techniques for active power filters: sliding mode control and proportional-integral control

This paper presents a three-phase shunt active power filter controlled by three different control strategies using a digital signal processor (DSP). The control techniques analyzed and compared are: sliding mode control (SMC), proportional-integral control (PI), and sliding mode control with proportional-integral controller (SMC-PI). Analysis and modeling of the shunt active power filter as well as simulation and experimental results are presented. The results show that the SMC controller has a better performance than PI and SMC-PI, allowing a low THD in the AC mains current and a fast transient response.

A Robust Nonlinear Control Scheme for a Sag Compensator Active Multilevel Rectifier Without Sag Detection Algorithm

In this paper, a robust nonlinear control scheme is proposed for the single-phase active multilevel rectifier (SPAMR) subject to voltage input sags. The scheme is based on the input-output model of the rectifier system combined with exact linearization achieved via generalized proportional-integral (GPI) control. The GPI controller provides enhanced robustness for the SPAMR against unexpected voltage sags and load changes. The main contribution of this paper resides on avoiding the need for voltage sags detection algorithms while improving the dynamic response of the SPAMR. Simulation and experimental results obtained on a 1-kVA SPAMR laboratory prototype are presented.

Voltage Sag Compensation in High-Quality AC/DC Converters Using the Single-Phase DQ Theory

Voltage sags are one of the most important power quality problems, affecting industrial and commercial customers. Industrial processes are particularly sensitive to relatively minor voltage sags. Utilities have been improved their fault-recovery capabilities, however it is still impossible to eliminate faults in the systems. Therefore, customers will have to improve the ride-through capability of the system equipment in their facilities. This paper presents the application of the single-phase DQ theory as a simple method to detect voltage sags in the AC mains obtaining the voltage peak value. This information can be used to achieve, by analytical manipulations, the input current adjusting during the sag, in order to maintain the load power constant. Applying the above considerations to a single-phase five-level PWM rectifier both objectives power factor correction in steady state and voltage sag compensation in transient state are gotten. Simulation and experimental results have been carried out in a 1 kVA, single-phase power converter

A Comprehensive Design Approach of Power Electronic-Based Distributed Generation Units Focused on Power-Quality Improvement

The undesirable harmonic distortion produced by distributed generation units (DGUs) based on power-electronic inverters presents operating and power-quality challenges in electric systems. The level of distortion depends on the internal elements of the DGUs as well as on the characteristics of the grid, loads, and controls, among others. This paper presents a comprehensive method, focused on power-quality indexes and efficiency for the design of microgrids with multiple DGUs interconnected to the ac grid through three-phase multi-Megawatt medium-voltage pulsewidth-modulated-voltage-source inverters (PWM-VSI). The proposed design method is based on a least square solution using the harmonic domain modeling approach to effectively consider explicitly the harmonic characteristics of the DGUs and their direct and cross-coupling interaction with the grid, loads, and the other DGUs. Extensive simulations and analyses against PSCAD are presented in order to show the outstanding performance of the proposed design approach.

An Optimal Selection of the References Generation Scheme for the DQ Theory to Compensate Unbalance, Reactive Power, Harmonic Distortion and Non Characteristic Harmonics

An optimal selection of parameters of a references generation scheme for the DQ theory is presented in this paper. With this selection, an active filter is theoretically able to perform an adequate compensation of all the most common polluting perturbations of electrical systems, such as unbalances, harmonic distortion, non characteristic harmonics, reactive power and power factor. This approach is only valid at steady state or for slow transient events, because the settling time of the active filter reaches a high value, almost three 60 Hz cycles. However, this is very useful for active filters as it will keep the system free of pollutions permanently

A Control Strategy to Improve Voltage Sag Ride-Through in Single-Phase Multilevel Active Rectifier

Voltage sags are one of the most important power quality problems, affecting industrial and commercial customers. These events are usually associated with a fault somewhere on the supplying power system. Industrial processes are particularly sensitive to relatively small voltage sags; therefore, customers will have to improve the ride-through capability of the system equipment in their facilities. This paper presents the application of a control strategy to a single-phase multilevel active rectifier in order to achieve a fast compensation and a small ripple in the DC bus during the voltage sag, maintaining the other benefits (power factor correction and input current harmonic components reduction). The proposed strategy is based on a classical PI voltage controller which parameters are modified when voltage sag occurs. The single-phase DQ theory is used to detect voltage sag and to make the compensation by means of a power estimator. Simulation and experimental results have been carried out in a 1 kVA, single-phase power converter

Step by step design procedure of an Independent-Wheeled Small EV applying EVLS

The main purpose of this paper is to present a step by step design procedure of an experimental EV powered by two electronically independent controlled induction machines. Additionally efforts are focused to develop high performance, low price traction system with low losses needed in the propulsion system. Emphasis in developing an EV it is based in its high efficiency (above 80%) compared with HEV (60%) and ICE (30%) technology