Adaptive Voltage Control of the DC/DC Boost Stage in PV Converters With Small Input Capacitor

Abstract—In the case of photovoltaic (PV) systems, an adequate PV voltage regulation is fundamental in order to both maximize and limit the power. For this purpose, a large input capacitor has traditionally been used. However, when reducing that capacitor’s size, the nonlinearities of the PV array make the performance of the voltage regulation become highly dependent on the operating point. This paper analyzes the nonlinear characteristics of the PV generator and clearly states their effect on the control of the dc/dc boost stage of commercial converters by means of a linearization around the operating point. Then, it proposes an adaptive control, which enables the use of a small input capacitor preserving at the same time the performance of the original system with a large capacitor. Experimental results are carried out for a commercial converter with a 40 μF input capacitor, and a 4 kWPV array. The results corroborate the theoretical analysis; they evidence the problems of the traditional control, and validate the proposed control with such a small capacitor.

(Index Terms—Adaptive control, photovoltaic converters, photovoltaic power systems, small-signal modeling, voltage control.)

A DC–DC Converter Based on the Three-State Switching Cell for High Current and Voltage Step-Down Applications

A DC–DC Converter Based on the Three-State

Switching Cell for High Current and Voltage

Step-Down Applications

Abstract—This paper presents a pulsewidth modulation dc–dc nonisolated buck converter using the three-state switching cell, constituted by two active switches, two diodes, and two coupled inductors. Only part of the load power is processed by the active switches, reducing the peak current through the switches to half of the load current, as higher power levels can then be achieved by the proposed topology. The volume of reactive elements, i.e., inductors and capacitors, is also decreased since the ripple frequency of the output voltage is twice the switching frequency. Due to the intrinsic characteristics of the topology, total losses are distributed among all semiconductors. Another advantage of this converter is the reduced region for discontinuous conduction mode when compared to the conventional buck converter or, in other words, the operation range in continuous conduction mode is increased, as demonstrated by the static gain plot. The theoretical approach is detailed through qualitative and quantitative analyses by the application of the three-state switching cell to the buck converter operating in nonoverlapping mode (D < 0.5). Besides, the mathematical analysis and development of an experimental prototype rated at 1 kW are carried out. The main experimental results are presented and adequately discussed to clearly identify its claimed advantages.

CONTACT US

M.SENTHILKUMAR

9500090804 , 9003012154

A Current Controller Design for Current Source Inverter-Fed AC Machine Drive System

A Current Controller Design for Current Source

Inverter-Fed AC Machine Drive System

Abstract—A current source inverter (CSI) requires a capacitor filter for the commutation of switching device as well as for attenuating switching harmonics. Hence, the CSI-fed ac machine has a second-order system in the continuous time domain. This paper presents a design methodology for the closed-loop current controller of the CSI-fed ac machine drive system. A multiloop current controller design using a pole/zero cancellation method is employed with a transfer function matrix. To decouple the crosscoupling terms which cause mutual interferences between the dand q-axes in the  synchronous reference frame, two types of controller are proposed and implemented using different decoupling method. Additionally, active damping methods are incorporated to  enhance the stability of the system. A stability analysis in discretetime domain is investigated to verify the feasibility of the proposed closed-loop current controller. To evaluate the effectiveness of the proposed current controller, computer simulations and experimental tests were performed and the results are discussed.

CONTACT US

M.SENTHILKUMAR

9500090804 , 9003012154