Renan C. Viero

Dynamic modeling of a ZETA converter in DCM applied to low power renewable sources

This paper presents the dynamic modeling of a ZETA converter in discontinuous conduction mode (DCM) applied to low power renewable sources using the generalized switch averaging technique. The whole system consists of a ZETA converter associated with a full bridge inverter operating at low frequency. Thus, the system works as a sinusoidal low power source. The ZETA converter plays the main role in this arrangement, producing a rectified sinusoidal current waveform synchronized with the power grid. Initially it is presented a brief analysis of the system, as well as the characteristics that make possible the dynamic analysis in DCM. The generalized switch averaging technique are discussed, and also the small-signal analysis of the ZETA converter. In order to validate the current study experimental and simulations results are presented.

Analog signal processing for photovoltaic panels grid-tied by Zeta converter

In this paper it is presented a detailed description of the analog implementation of the control for a DC-AC converter composed by a DC-DC Zeta converter and a low frequency inverter. Using only analog components, it was developed the MPPT technique based on linearization of solar panel characteristic around the MPP, a feedforward control and a robust PWM sine wave modulator. This simple and low cost solution was designed to be used in grid connected rooftop photovoltaic panels (PV). In scenery where an entire city area could be used to generate extra power, reducing the necessity of huge central power plants, module integrated inverters will play an important role on grid connection of PV systems with high reliability due to the high level of redundancy. The experimental results show that this simple cost effective solution is able to extract maximum power from PVs with low current harmonic content.

Dynamic modeling of a sinusoidal inverter based on ZETA converter working in DCM for PV arrays

This paper presents a dynamic modeling study for a ZETA converter working in discontinuous conduction mode (DCM) applied to low power renewable energy sources using the generalized switch averaging technique. The modeling is performed considering only resistive loads. The whole system consists of a ZETA converter, using a sinusoidal pulse width modulation (PWM), associated with a full-bridge (FB) inverter, operating at low frequency, in order to synthesize a sinusoidal waveform at its output. Thus, the system works as a sinusoidal low power source. Initially it is presented a brief analysis of the system, as well as the characteristics that made possible the dynamic analysis in DCM. The generalized switch averaging technique is discussed, and also the small-signal analysis of the ZETA converter. In order to validate the current study experimental and simulation results are presented.

Low power solar system grid-tied with MPPT based on temperature compensation

This paper presents a power converter for grid connection of renewable energy sources, consisting of a ZETA converter associated with a bridge inverter operating at low frequency. The Zeta converter, operating in the discontinuous conduction mode (DCM), produces a rectified sinusoidal current waveform synchronized with the electric grid. The full-bridge inverter, connected to the output of the Zeta converter, is to reverse every 180° the current generated by the Zeta converter. A low cost MPPT based on the linearization of PV panels characteristics and temperature compensation is presented. An analysis of the Zeta converter operating in DCM is presented with converter design considerations, followed by the control strategy and experimental results for a 100 Wp PV system.

A PV module-integrated inverter using a Ćuk converter in DCM with island detection scheme

This paper reports a study on a grid-tied photovoltaic system, using a microinverter based on Ćuk converter working in DCM. Since, when the Ćuk converter is working in DCM, its output voltage presents a linear behavior in relationship to its duty cycle. Therefore, the duty cycle must have a sinusoidal behavior, in absolute value, in order to generate a rectified sine current waveform, at its output. The connection of a full bridge current source inverter in cascade with the Ćuk converter, allows obtaining a sinusoidal current waveform at the microinverter output. One of the most important challenges on microgeneration systems is the island detection. In this sense, if the system is unable to detect the islanding, this may cause power quality degradation, electrical safety threats, especially related to maintenance crews, and damage to third-party devices connected to the same power grid.

Computational model of the dynamic behavior of the ZETA converter in discontinuous conduction mode

This paper presents a computational model of the dynamic behavior of the ZETA converter working in discontinuous conduction mode (DCM), as well as a design example of the feedback control of this converter using a PID controller. In turn, the PID controller is tuned by a dedicated block of the MATLAB™ design optimization library, thanks to the computational model of the ZETA converter. In order to validate the new computational model some simulations were performed using the PSIMTM simulation tool and, finally, a prototype was built and tested. The obtained results confirm that the new computational model of the dynamic behavior of the ZETA converter in DCM is an effective tool to represent accurately the converter dynamic behavior and consequently, a helpful means to design feedback controllers.

MPPT techniques applied to the control of a module-integrated inverter grid-connected based on Zeta converter for PV panels

This paper presents the study and implementation of maximum power point tracking techniques (MPPT) applied to a module-integrated inverter based on a Zeta converter. The module-integrated inverter allows electricity generated by a PV solar panel to be injected into the commercial power grid. This structure provides significant advantages over the structure that employs the combination of multiple panels connected to a large single inverter (central inverter). Among the advantages offered by the module-integrated structure can be highlighted: modularity, allowing the natural parallelism of the systems, increased system reliability, because in case of failure of a module the plant remains powered after all energy is provided by several PV panels and their module-integrated inverters that work independently, and finally, there is the possibility of obtaining the MPPT individually, which is quite interesting in large systems, where shading may occur in only a few panels. The system employed in this work consists in the association of a PV array to a Zeta converter in cascaded with a single phase full-bridge inverter operating synchronized with the power grid at the same frequency. A Zeta converter working in DCM is responsible for the synthesis of a rectified sinusoidal current waveform synchronized with the grid. The CSI is used to invert the current every 180°. In this study three MPPT techniques were examined, namely Constant Voltage, Perturb and Observe and Hill Climbing. A prototype was built using digital signal processing. The obtained results validated the presented study, described in the work.

Designing closed-loop controllers using a MatlabP ® dynamic model of the Zeta converter in DCM

As is well known the Zeta converter is a fourth-order system. Therefore, the selection of the type of feedback controllers and its design, it is not an easy task. Usually many restrictions must be met in closed-loop control systems. For instance, it is necessary ensure system stability, as well as, guarantee that transient and steady-state responses are under preset limits. In order to design a controller (P, I, PD, PI, PID, Lead, Lag, Lead-Lag), is usually necessary to know the system plant. However, unfortunately, the system plant is not always available and even when it is accessible, designers must have good knowledge of control systems theory in order to design properly the controllers. Aiming to make the compensators design a simpler task to everyone this paper presents a computational model of the dynamic behavior of the Zeta converter working in discontinuous conduction mode, as well as, two design examples of feedback controllers. Two compensators were designed using MATLAB® and SIMULINK® specifically by means of the design optimization library, which could be used thanks to the computational model of the Zeta converter. It was performed a set of simulations using the PSIM® software, in order to validate the proposed computational model. The obtained results confirm that the computational model of the dynamic behavior of the Zeta converter in DCM is useful to design feedback controllers and also to reduce the development time of the compensators.

A micro inverter based on Ćuk converter for PV modules with anti-islanding and MPPT schemes

This paper describes a study, which enables the implementation of a microinverter for grid-tied photovoltaic applications. The system consists of a Ćuk converter in cascade with a full-bridge current source inverter. The Ćuk converter, working in DCM, synthesizes a sinusoidal current waveform, in absolute value, synchronized with the power grid. A simple square wave (SQW) full bridge current source inverter is connected in cascade with the Ćuk converter, in order to obtain a sinusoidal current waveform at its output, the SQW control aims to minimize the inverter switching power losses. The connection of microgeneration systems into the utility grid can bring some challenges, as the islanding detection and the tracking of the PV module maximum power point, for instance. In this sense, a non-detected islanding may cause: degradation of power quality, threats to safety of maintenance crews, damage to third party equipment connected to the same power grid. In order to maximize the power production of the photovoltaic module it is mandatory, to make use of a MPPT algorithm. The implemented algorithm consists of a variation of the P&O method, instead of a fixed perturbation magnitude, the develop algorithm makes use of the derivative of the PV module voltage, in order to determine the magnitude of the perturbation. The inverter control is implemented in a Matlab/Simulink© environment in association with a dSPACE© controller board for research and development (DS1104 R&D).