Mohamed Orabi

Nonlinear dynamics of power-factor-correction converter

The boost power-factor-correction (PFC) converter with average-current-mode control is a nonlinear system due to the effects of the multiplier and a large variation of the duty ratio. Although its stability analysis must be studied depending on a nonlinear model, most prior research attempted to make some assumptions to force this nonlinear system to be linear. As a result, the practical dynamics and the nonlinear phenomena were disregarded. In this paper, two kinds of nonlinear phenomena are detected under the conditions that are considered to be stable by the prior criteria: one is period-doubling bifurcation and the other is chaos. Stability maps and phase-plane trajectories are introduced at different loads to clarify the power factor and also the instability regions. It is clear that the output storage capacitor is a main contributing parameter on the system stability, therefore, bifurcation maps are developed to determine the accurate minimum output capacitance value that assures the system stability under all operating conditions. Also, PFC converter stability is explained and judged by comparing the consequence of charging and discharging energy in the output capacitor.

Matlab/Pspice hybrid simulation modeling of solar PV cell/module

The power generated by solar photovoltaic (PV) module depends on surrounding irradiance, temperature and shading conditions. Under partial shading conditions (PSC) the power from the PV module can be dramatically reduced and maximum power point tracking (MPPT) control will be affected. This paper presents a hybrid simulation model of PV cell/module and system using Matlab®/Simulink® and Pspice®. The hybrid simulation model includes the solar PV cells and the converter power stage and can be expanded to add MPPT control and other functions. The model is able to simulate both the I-V characteristics curves and the P-V characteristics curves of PV modules under uniform shading conditions (USC) and PSC. The model is used to study different parameters variations effects on the PV array. The developed model is suitable to simulate several homogeneous or/and heterogeneous PV cells or PV panels connected in series and/or in parallel.

Switched inductor boost converter for PV applications

This paper introduces a boost converter with high dc gain as a solution for partial shading of photovoltaic (PV) module. Switched inductor boost converter (SIBC) is introduced by replacing the inductor of the boost converter with a switched inductor branch. As a result, the conversion gain ratio can be increased. The proposed converter is used as an interface between the PV system and the load. A Maximum Power Point Tracking (MPPT) control is applied to extract the maximum power of the PV module. Analyses, simulation, and experimental results are provided to validate the operation of the converter.

Modeling of switching frequency instabilities in buck-based DC–AC H-bridge inverters

In this paper, the dynamical behavior of a full bridge DC–AC buck inverter controlled by fixed frequency and PWM is studied. After showing that the system can undergo both period-doubling and Neimark–Sacker bifurcation at the fast scale (switching period) by using the exact switching model, an exact solution discrete-time model able to predict both instability phenomena is derived. The model is obtained without making the quasi-static approximation and it can be used to obtain the useful operation region in the multi-dimensional design parameter space from time domain simulations in a very fast and accurate manner. Based on the study of the system, some design guidelines are provided. Copyright

A single stage SEPIC PFC converter for LED street lighting applications

Light Emitting Diodes (LEDs) with their current performances have been proved to be the most suitable solution for street lighting applications. Nowadays, a topic of interest in this context is the design for electronic driver in order to take the advantage of LEDs performances. However, requirements such as high power factor, long life time, accurate current control and high efficiency pose challenges to the design of LED driver circuits. Single-stage power factor correction (PFC) topologies are preferred here for their advantages of lower cost and near unity power factor, while adding a separated PFC stage will surely increase the cost. This paper presents a high efficiency single-stage LED lamp driver for street lighting applications based on SEPIC PFC converter topology operating in continuous conduction mode (CCM). This converter has achieved high efficiency and high power factor all over the operating range with low total harmonic distortion (THD). Simulation results are provided to demonstrate the effectiveness of the proposed driver. Then, a laboratory prototype is built to verify the feasibility of the proposed LED lamp driver.

Asymptotic Slow-Scale Stability Boundary of PFC AC–DC Power Converters: Theoretical Prediction and Experimental Validation

A unified approach for the stability analysis of both preregulator and two-stage power factor correction (PFC) ac-dc converters is presented. Practical and accurate analytical expressions for the stability boundary are obtained by studying the dynamics of the first harmonic component. The resulting model of this dynamics has an equilibrium point at the origin of the harmonic state space. In the case of a stable equilibrium point, the first-order component converges to zero, and the system oscillates at twice the line frequency. If the equilibrium point loses stability, another equilibrium point depending on high-order harmonics will be reached while the real system will exhibit a period-doubling phenomenon leading to subharmonic oscillations. It is demonstrated that the stability boundaries depend on the power level. Numerical simulations and experimental results in both a preregulator and a complete two-stage PFC converter validate the approach.

Stabilizing Technique for AC–DC Boost PFC Converter Based on Time Delay Feedback

It is well known that the ac-dc power factor correction (PFC) boost preregulator can present instability at the line frequency. This nonlinear phenomenon can jeopardize the system performances by increasing the total harmonic distortion and decreasing the power factor. In this brief, a new stabilizing technique is applied using time delay feedback when the system exhibits slow-scale instability under a traditional controller. First, the technique is applied to the averaged model. The results are then validated by numerical simulations using power simulator package. An analytical expression for the stability domain is also provided. It is proven that the proposed technique introduces many advantages to the most and widely used average current mode control through widening the stability region of the PFC converter. Moreover, this technique can also bring the same advantages to other existing commercial control methods for boost and other PFC topologies.

High gain single-stage inverter for photovoltaic AC modules

In this paper, a high gain single-stage buck-boost grid-connected system is proposed. The proposed system consists of a high voltage gain — high efficiency — switched inductor buck-boost converter (SIBBC) and a folded cascade H-bridge inverter. The proposed converter switch is derived with a sinusoidal modulation, so that the converter output voltage is a rectified sine wave which requires only a folded cascade as a second stage. Therefore, H-bridge is used to fold converter output voltage at fundamental frequency that eliminates the switching loss. The proposed system is used to connect the PV module to the grid with achieving maximum Power Point Tracking (MPPT) control; AC module. The converter operates in DCM to inject a sinusoidal current into the grid with unity power factor. The proposed dc-ac system has some advantages such as low cost, small size and simple control. In addition, the grid connection, MPP, and unity power factor controls are executed through only one switch, the converter switch. A prototype has been built and tested for validation. Some selected simulation and experimental results have been provided.

A novel modeling of instability phenomena in PFC converter

Power factor correction (PFC) converters have become the norm in almost all electronic systems. Most high-frequency power factor correctors use resistor emulation to achieve a near-unity power factor and a small line current distortion. This technique requires forcing the input current with an average current mode control to flow the input voltage. Stability of this system is discussed by using the previous linear model. However, new instability phenomena are detected in the stable region expected by the prior linear model. Therefore, this paper is concerned with the detection of the unstable phenomena in a PFC circuit. Period doubting bifurcation and chaos instability are new instability phenomena in a PFC circuit. Lissajous curves are introduced to explain these unstable phenomena. The study reveals that the PFC converter losses its stability as a result of decreasing the load current.

Development of high gain and efficiency photovoltaic system using multilevel boost converter topology

This paper presents the analysis and operation of a PV system using multilevel dc-dc topology as a high gain converter in addition to applying Maximum Power Point Tracking (MPPT) technique. The multi-level boost converter parameters have been adjusted to achieve the high efficiency and high gain target results. In addition, a full bridge inverter is used to connect the generated power from the PV into the grid. The total system has been analyzed and then simulated using MATLAB to prove the idea. Then, a set-up of experimental results has been provided to validate the simulation results using FPGA control.