Khalid Rustom

Statistical modeling of DSP-based Hill-climbing MPPT algorithms in noisy environments

The effect of measurement noise on DSP-based maximum power point tracking (MPPT) algorithms is investigated in this paper. Based on the probabilistic characteristics of noise signals, a statistical model is constructed that allows quantitative analysis of the behavior of such algorithms both during transients and in steady-state. This model is then used to classify tracking problems into those presented by noise, and others resulting from other non-idealities such as measurement bias. It is then used to inspect different noise fighting techniques in order to predict their validity, and to suggest more relevant techniques. The results arrived at are then experimentally verified and confirm the predictions of the statistical model

Maximum Energy Harvesting Control for Oscillating Energy Harvesting Systems

This paper presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.

Effect of Measurement Noise and Bias on Hill-Climbing MPPT Algorithms

Erroneous measurement of solar array voltage and current degrades the performance of hill-climbing, maximum power point tracking (MPPT) systems. This degradation is observed as a reduced climbing rate, erroneous settling point, and/or random operating point excursions. The effect of measurement bias and noise on MPPT performance is analyzed. Tracking problems are then classified according to their cause, which allows for easier debugging of a faulty tracker. The effectiveness of several error-mitigating techniques is then studied, and recommendations are given accordingly. Conclusions of the analysis are then experimentally verified.

Universal input single-stage PFC AC/DC converter with reduced DC-bus voltage stress

High DC bus voltage stress and low conversion efficiency limit the practical application for single stage power factor correction (PFC) AC-DC converters. This paper presents a cost-effective approach to alleviate these issues based on a conventional BIFRED AC/DC converter. In the proposed topology, a flyback transformer and a small serial connected inductor are implemented to replace the traditional input PFC inductor, and a cost-efficient lossless snubber is also proposed to reduce the turn-off spike of the main switch. The experimental results of a 20 V@4.5 A prototype indicate that the proposed technique can suppress the DC voltage below 400 V through the entire universal input range, while keeping the efficiency and power factor above 81% and 0.95 respectively.

Asymmetric half bridge soft-switching PFC converter with direct energy transfer

A single-stage power factor correction (PFC) AC/DC converter with a direct energy transfer feature is proposed in this paper. An asymmetric half-bridge topology is used as the DC-DC cell for its inherent ZVS capability, and a direct energy transfer PFC cell is introduced to improve the conversion efficiency. Its operational principles are discussed in detail, and simulation and experimental results are also presented to verify the functionality of this converter.

Pulse frequency modulation with soft-switching flyback single-stage inverter

A Pulse Frequency Modulation (PFM) with Zero-Current-Switching (ZCS) flyback inverter is proposed in this paper. By using half-wave quasi-resonant ZCS flyback resonant converter and PFM control, this topology significantly alleviates switching losses. A detailed analysis revealed nonlinearity in the power stage when the secondary side inductance gets smaller. A modified structure with a secondary side MOSFET is also proposed to solve this issue. Finally, the experimental results of 250W converter are provided.

Recent advances in single-stage power factor correction

This paper presents an overview of various interesting power factor correction techniques for single-phase applications. The discussion includes commonly-used control strategies and various types of converter topologies. Included is a comparative study of these strategies, with the major advantages and disadvantages is highlighted. We will emphasize the single-stage topologies, its drawbacks and some promising solutions.

Bi-flyback single-stage PFC converter with valley switching technique

Valley switching technique can reduce the turn-on switching losses in flyback topology by discharging the MOSFET capacitor before the switch is turned on. In this paper, valley switching technique is applied to single-stage power factor correction (PFC) converters to achieve improved performance. Detailed operation principle, simulation results and experimental data are included.

Five-Terminal Switched Transformer Average Modeling and AC Analysis of PFC Converters

A simple and accurate five-terminal switched transformer average model is proposed and its generalized equations are derived. The proposed model is capable of both time domain and AC analysis of DC-DC, AC-DC, and is especially suitable for single-stage power factor correction (PFC) converters. Unlike other models presented in literature, the proposed switching cell includes the transformer leakage inductance, an intermediate bus input, and still addresses both continuous and discontinuous conduction modes. The model was applied to two topologies, the bi-flyback and the flyboost parallel/series forward converters. The time domain results show great accuracy when compared with the slower and time consuming switching simulation. The AC analysis is also predicted with greater accuracy exposing the dynamics of such converters, a task that was not as easily addressed before when the unique characteristics of single-stage are considered. The frequency domain analysis was also verified with experimental results for the bi-flyback converter. The model is very relevant to isolated flyback converters including the PFC examples provided, which are not as easily or as accurately modeled by other approaches.

Bi-directional DCM DC to DC converter for hybrid electric vehicles

This paper presents a bi-directional DC to DC converter with a unique concept in control. The converter was designed for hybrid electric vehicles, so size becomes a pressing design parameter. For that reason a buck converter in DCM was used to realize the DC to DC converter. The DCM operation was used in order to shrink the magnetic components, as described in the paper. However, DCM converters are not inherently bi-directional. The unique controller developed here allows for the DCM converter to seamlessly direct power from low voltage side to high voltage side and from high voltage side back to low voltage side. A power management technique was also developed to handle a wide array of conditions present in hybrid electric vehicle applications. The technology developed here offers the designer the option to utilize the benefits of a buck converter in DCM while still maintaining a bi-directional power flow.