Simone Buso

Comparison of current control techniques for active filter applications

This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations.

Robust dead-beat current control for PWM rectifiers and active filters

The paper analyses the stability limitations of the digital dead-beat current control applied to voltage-source three-phase converters used as PWM rectifiers and/or active filters. In these applications the conventional control algorithm, as used in drive applications, is not sufficiently robust and stability problems may arise for the current control loop. The current loop is, indeed, particularly sensitive to any model mismatch and to the possibly incorrect identification of the model parameters. A detailed analysis of the stability limitations of the commonly adopted dead-beat algorithm, based on a discrete-time state space model of the controlled system, is presented. A modified line voltage estimation technique is proposed, which increases the controls robustness to parameter mismatches. The results of the theoretical analysis and the validity of the proposed modification to the control strategy are finally verified both by simulations and by experimental tests.

Simple digital control improving dynamic performance of power factor preregulators

This paper presents the practical implementation of a fully digital control for boost power factor preregulators (PFPs). The control algorithm, which is simple and fast, provides a significant improvement in the systems dynamic performance compared to the usual analog control techniques. The paper discusses the design criteria and the actions taken for the implementation of the digital control, which is performed by means of a standard microcontroller (Siemens 80C166). The effectiveness of the approach is assessed by experimental tests.

Low-Complexity MPPT Technique Exploiting the PV Module MPP Locus Characterization

This paper proposes a method for tracking the maximum power point (MPP) of a photovoltaic (PV) module that exploits the relation existing between the values of module voltage and current at the MPP (MPP locus). Experimental evidence shows that this relation tends to be linear in conditions of high solar irradiation. The analysis of the PV module electrical model allows one to justify this result and to derive a linear approximation of the MPP locus. Based on that, an MPP tracking strategy is devised which presents high effectiveness, low complexity, and the inherent possibility to compensate for temperature variations by periodically sensing the module open circuit voltage. The proposed method is particularly suitable for low-cost PV systems and has been successfully tested in a solar-powered 55-W battery charger circuit.

Uninterruptible power supply multiloop control employing digital predictive voltage and current regulators

A digital control technique for the inverter stage of uninterruptible power supplies (UPSs) is described, which is based on voltage and current predictive regulators. Its aim is to achieve a deadbeat dynamic response for the controlled variables (output voltage and inverter current). The controller maintains the advantageous conventional multiloop structure and is capable of guaranteeing a high-quality dynamic performance. Moreover, its design is extremely simple and requires only a reasonably accurate knowledge of the output filter parameters. Finally, the only sensed variables are the output voltage and the converter output current. The validity of the proposed strategy is demonstrated by means of simulation and experimental results referring to a single-phase UPS laboratory prototype (1 kVA).

Performance Degradation of High-Brightness Light Emitting Diodes Under DC and Pulsed Bias

This paper presents the results of an experimental investigation of the performance of commercially available high-brightness light emitting diodes (HBLEDs). Three different families of white HBLEDs from three different manufacturers are considered. The main issues taken into account and reported in detail are the following: quality of the emitted light, impact of the driving strategy on the expected device lifetime, thermal management and related aging effects. The execution of a large number of accelerated stress tests reveals the weaknesses of the technology with respect to thermal degradation and the sensitivity of the device performance degradation to the adopted driving strategy. Furthermore, square-wave driving has been compared to conventional dc driving in terms of device performance and reliability. Comparison has been carried out for the same average current value of the driving waveforms. It has been found that square-wave driving can be an effective alternative to dc driving in terms of device efficiency only for high duty cycles. For low duty cycles, worse performance was detected due to the saturation of efficiency at high peak current levels. Reliability tests did not univocally indicate whether the use of pulsed bias can be more convenient than dc driving in terms of lumen maintenance. The three families of devices submitted to dc and pulsed stresses showed different behaviors, indicating that stress kinetics strongly depends on the LED technological structure and package thermal design.

Design and fully digital control of parallel active filters for thyristor rectifiers to comply with IEC-1000-3-2 standards

This paper presents the implementation of a digitally controlled parallel active filter for a thyristor rectifier with inductive load. Using a state-of-the-art digital signal processor (DSP) platform (ADSP21020 and ADMC200), a fully digital control of the system, based on the dead-beat control of inverter currents and space vector modulation, is implemented. The intrinsic calculation delay of the dead-beat algorithm is shown to represent a serious hurdle for the achievement of a satisfactory compensation quality. In particular, meeting the IEC 1000-3-2 standards for class A equipment appears to be quite difficult, especially in the high-frequency range. This paper investigates the effects of the input passive filters and power converter design on the systems performance and describes the implementation of the digital control by means of the specified hardware. Experimental results are finally given to evaluate the achieved performance.

Uninterruptible power supply multi-loop control employing digital predictive voltage and current regulators

A digital control technique for the inverter stage of uninterruptible power supplies (UPSs) is described, which is based on voltage and current predictive regulators. Its aim is to achieve a dead-beat dynamic response for the controlled variables (output voltage and inverter current). The controller maintains the advantageous conventional multi-loop structure and is capable of guaranteeing a high quality dynamic performance. Moreover, its design is extremely simple and requires only a reasonably accurate knowledge of the output filter parameters. Finally, the only sensed variables are the output voltage and the converter output current. The validity of the proposed strategy is demonstrated by means of simulation and experimental results referring to a single-phase UPS laboratory prototype (1 kVA).

A Line-Interactive Single-Phase to Three-Phase Converter System

This paper describes a line-interactive single-phase to three-phase converter. A typical application is in rural areas supplied by a single-wire with earth return system. The traditional objective of feeding a three-phase induction motor is not anymore the main concern for such conversion. Due to the evolution of the farm technology, some of the local loads (as electronic power converters, computers, communication equipments, etc) require high power quality that is intended as sinusoidal, symmetrical, and balanced three-phase voltage. Additionally, to maximize the power from the feeder, the system provides a unity power factor to the grid. A three-phase voltage source inverter-pulsewidth modulation converter is used for this purpose. The power converter processes a fraction of the load power and the energy necessary to regulate the dc link voltage. As it does not need to supply active power, it is not necessary to have a source at the dc side. However, if island mode operation is needed, a dc source must be available at the dc link to supply the load. The control strategy, design criteria, and experimental results are presented

Analysis of a High-Power-Factor Electronic Ballast for High Brightness Light Emitting Diodes

This paper analyzes the performance of a high-power-factor AC-DC converter for the supply of high-brightness light emitting diodes (HBLEDs). The considered topology is a D2 one (i.e. a topology that, working in continuous conduction mode, has a voltage conversion ratio that is a function of the duty-cycle squared), working in one of its possible discontinuous modes. No line-frequency energy storage element is used so that the LED current is pulsating at twice the line frequency, with a small high-frequency ripple on top. The impact of such pulsating current supply on LED optical performance and reliability is also evaluated by comparison with standard DC current supply