This work presents a power adaptor device, referred as Smart Panel Device, allowing the connection of additional energy sources and storage elements to a domestic PV grid-connected system. The adaptor output port is designed to behave as a power source/sink, thus enabling its hot-swap parallel connection to renewable power sources without modifying their Maximum Power Point. Moreover, the adaptor device features a power characteristic with a single controllable MPP and allows the control of the injected power within the operating range of the DC-AC grid-connected inverter. The work presents the design principles of such device by describing the operation of a sliding-mode controlled quadratic boost converter. The proper operation of the device is experimentally verified for several scenarios in a small PV-based microgrid system including a fuel cell stack, a 1 kW three-phase wind turbine, a battery charger-discharger and commercial grid-connected PV inverters.

A cascade control strategy is employed in the boost inverter to generate a sinusoidal signal at grid frequency with very low distortion. The internal loop of the cascade employs a switching surface based on the difference of the inductor currents to induce sliding motions in the power stage. The outer loop in turn establishes the reference of the internal loop and ensures the tracking of an external sinusoidal signal at 50 Hz. The reported approach is analytical and is based on the equivalent control method. The root locus of the capacitor voltages at the equilibrium point of the inner loop is obtained assuming a constant value of the loop reference. In the particular case of a zero reference, sinusoidal variations at grid frequency are superposed to the corresponding equilibrium point and the resulting ideal dynamics are linearised yielding the control to output transfer function of the system. A proportional-integral (PI) compensator is designed for both large bandwidth and small phase error. Experimental results in a 500 W prototype are in perfect agreement with the analytical predictions.

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A study of a DC–DC boost converter fed by a photovoltaic (PV) generator and supplying a constant voltage load is presented. The input port of the converter is controlled using fixed frequency pulse width modulation (PWM) based on the loss-free resistor (LFR) concept whose parameter is selected with the aim to force the PV generator to work at its maximum power point. Under this control strategy, it is shown that the system can exhibit complex nonlinear behaviors for certain ranges of parameter values. First, using the nonlinear models of the converter and the PV source, the dynamics of the system are explored in terms of some of its parameters such as the proportional gain of the controller and the output DC bus voltage. To present a comprehensive approach to the overall system behavior under parameter changes, a series of bifurcation diagrams are computed from the circuit-level switched model and from a simplified model both implemented in PSIM© software showing a remarkable agreement. These diagrams show that the first instability that takes place in the system period-1 orbit when a primary parameter is varied is a smooth period-doubling bifurcation and that the nonlinearity of the PV generator is irrelevant for predicting this phenomenon. Different bifurcation scenarios can take place for the resulting period-2 subharmonic regime depending on a secondary bifurcation parameter. The boundary between the desired period-1 orbit and subharmonic oscillation resulting from period-doubling in the parameter space is obtained by calculating the eigenvalues of the monodromy matrix of the simplified model. The results from this model have been validated with time-domain numerical simulation using the circuit-level switched model and also experimentally from a laboratory prototype. This study can help in selecting the parameter values of the circuit in order to delimit the region of period-1 operation of the converter which is of practical interest in PV systems.

An efficiency comparison between a boost converter implemented with silicon (Si) devices and the same converter implemented in the other three cases, that is, employing two combinations of silicon carbide (SiC) devices and a mixture of Si and SiC elements is presented. The converter has been designed for high-voltage low-power applications required by light-emitting diode (LED) lighting. The comparison is performed on an equal basis and discusses the influence on the converter efficiency of the semiconductor power devices and the passive components. The experiments are carried out in a single-stage boost converter prototype delivering a maximum output voltage of 1200 V when supplied by a 12 V battery. The measurements show that the highest efficiency is obtained when the power transistor is implemented by a normally-off junction field-effect transistor and the diode by a SiC Schottky device with a small parasitic capacitance. The implementation with the highest efficiency has been selected for supplying a light spot of 320 LEDs in series, which results in an output voltage of 956 V and an output power of 20.6 W.

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salAbstract-Hybrid Distributed systems include many sources, storage elements, and various local loads, connected to a common distribution bus. In this work, different matching methods to adapt a 3-phase wind alternator to a variable DC-bus are reviewed, and finally a modular solution based on single-phase Boost-based PFC's is proposed. Nevertheless, Boost modules must be adapted to operate with non-isolated sources, like 3-4 wire, 3-phase generators. Magnetic coupling is introduced here to enhance the isolation among phases, reducing also converter losses and size. Sliding mode approach has been applied to the whole converter as a single unit, to verify that independent regulation of all phase modules was possible, even sharing a common output capacitor. To verify the theoretical analysis, a 1.5 kW prototype has been built confirming independent phase control and good sinusoidal input waveforms.978-1-4244-8807-0/11/$26.00 ©2011 IEEE 125