Pedro M. de Almeida

Grid connected PV system with load power compensation capability using sliding mode control

This paper presents the modelling and design steps for a grid connected Photovoltaic System using a single-stage three-phase Voltage Sourced Converter. As the PV array is directly connected to the DC bus, a Maximum Power Point Tracking algorithm provides the reference voltage for an outer DC voltage control loop. The interface converter is controlled using a direct power sliding mode control without any synchronization circuit. This is possible because the converters control is done in the stationary reference frame. Besides the active power injection, this system is able to compensate the reactive and harmonics power consumed by the loads. For the pattern switching, space vector modulation is used to generate constant switching frequency. Simulation results are presented to validate the proposed system during the active power injection and load compensation.

Grid connection considerations for the integration of PV and wind sources

This paper makes suggestions, based on the current grid codes, for different requirements that may be adopted by the transmission system regarding the connection of large wind and photovoltaic power plants to medium and high voltage networks. The main purpose is to present a proposal which harmonizes the requirements for renewable energy sources with electronic interface. Taking into consideration the characteristics of the point of connection, based on the stiffness and other relevant issues as background distortion and hosting capacity, in order to facilitate the integration of RES without compromising the integrity of the transmission and distribution grids.

Characterization of electronic converters by time-varying harmonic phasors and waveforms

As an enabling technology, power electronics has the ability to provide effective and intelligent solutions for the grid of the future; however, the complexity and interaction with the rest of the system is non-trivial and requires careful studies. Among the issues to be addressed is the behavior of electronic converters under transient conditions. This paper investigates the behavior of electronic converters via time-frequency decomposition methods. The nonlinear electronic load is characterized by the time-varying harmonics during transient conditions such as voltage sags and variable voltage distortions. In the past, analytical expressions have been used to determine the harmonic current locus (in steady state condition) for different operating points. With the development of time-frequency decomposition tuned to the harmonic frequencies the transient performance of the harmonics can be observed with higher time resolution. This new approach enables researchers and engineers, for the first time to look into the transient behavior of harmonics and, consequently better understand the associated phenomena from a time-varying harmonic perspective. This method may become useful for determining the impact of the aggregation of multiple power electronic front-end devices. The approach may also help in setting up protection schemes based on the excursions of prominent harmonics during transient conditions.

Topology and control of a two-phase residential PV system with load compensation capability

This paper describes the topology and control scheme of a photovoltaic system for two-phase three-wire residential consumers. The system is composed basically of a photovoltaic array, dc-link and a grid-interface three-phase voltage sourced converter. The paper describes in detail how this system can work in an installation that uses two-phases and neutral derived from a three-phase distribution system. The incremental conductance technique is used to track the maximum power point. All generated power is used to feed the load or injected to the grid. Simultaneously to active power injection, the interface converter is also controlled to perform reactive power and current harmonics compensation. A single-phase instantaneous powers technique is used to obtain reference currents. A predictive controller used to generate converter switching signals is described as well. Simulation results are presented to confirm the suitability of the proposed topology and control scheme.

Sliding mode control of a shunt Active Power Filter with indirect current measurement

The main objective of this work is to investigate an indirect current control scheme based on slide mode approach to regulate the currents of a three-phase Active Power Filter (APF) in such a way to improve the quality of the power supplied by a diesel generator set. The indirect current control scheme provides the signal reference to active power filter controller without the need of measurement of the load currents. A sliding mode controller is designed in the inner control loop to assure the APF tracks the reference signals with a small amplitude error and a short time delay. A space vector modulation is used to generate the switching pattern for the voltage source converter. Simulation results are presented to validate the proposed control scheme.

Multi-physical modeling: An integrated way of understanding the dynamics of electric grids

This paper presents the modeling and simulation of a subsynchronous resonance using Simscape in a multi-physical environment. It is shown that through this new modeling approach it is possible to visualize and better understand how the mechanical and electrical systems interact with each other during a subsynchronous resonance. The use of multi-physical domain simulation allows engineers and designers to comprehend sophisticated and complex systems with interactions among several physical domains. It also helps to find flaws and foresee potential interaction problems. A subsyncronous resonance case is used as an example to demonstrate the utility of the tool.