Shelas Sathyan

Soft-Switching DC–DC Converter for Distributed Energy Sources With High Step-Up Voltage Capability

This paper presents high step-up dc-to-dc converter for low voltage sources such as solar photovoltaics, fuel cells, and battery banks. To achieve high voltage gain without large duty cycle operation, combination of coupled inductor and switched capacitor voltage doubler cells are used. By incorporating active clamp circuit, voltage spike due to the leakage inductance of the coupled inductor is alleviated and zero-voltage switching turn on of the main and auxiliary switch is obtained. Due to the use of MOSFETs of low voltage rating and soft turn on of the switches, conduction loss and switching losses are reduced. This improves the efficiency and power density of the converter. The proposed converter can achieve high voltage gain with reduced voltage stress on MOSFET switches and output diodes. Design and analysis of the proposed converter is carried out, and finally, a 500-W experimental prototype is built to verify theoretical analysis.

ZVS–ZCS High Voltage Gain Integrated Boost Converter for DC Microgrid

A nonisolated soft-switched-integrated boost converter having high voltage gain is proposed for the module-integrated PV systems, fuel cells, and other low voltage energy sources. Here, a bidirectional boost converter is integrated with a resonant voltage quadrupler cell to obtain higher voltage gain. The auxiliary switch of the converter, which is connected to the output port acts as an active clamp circuit. Hence, zero voltage switching turn-on of the MOSFET switches are achieved. Coupled inductors leakage energy is recycled to the output port through this auxiliary switch. In the proposed converter, all the diodes of the quadrupler cell are turned off with zero-current switching (ZCS). This considerably reduces the high-frequency turn-off losses and reverse recovery losses of the diodes. ZCS turn-off of the diodes also remove the diode voltage ringing caused due to the interaction of the parasitic capacitance of the diodes and the leakage inductance of the coupled inductor. Hence, to protect the diodes from the voltage spikes, snubbers are not required. The voltage stress on all the MOSFETs and diodes are lower. This helps to choose switches of low voltage rating (low RDS(ON)) and, thus improve the efficiency. Design and mathematical analysis of the proposed converter are made. A 250-W prototype of the converter is built to verify the performance.

Comparative evaluation of synchronization techniques for grid interconnection of renewable energy sources

This paper presents comparative performance evaluation of conventional SRF-PLL, existing adaptive notch filter (ANF) and an amplitude adaptive notch filter (AANF) based synchronization techniques used for converter-interfaced renewable energy systems. In addition, real time implementation and extraction of frequency and amplitude of the input grid voltage signal by all the three techniques has been presented. Comparative analysis has been done based on their ability in extracting amplitude and frequency variation of the input grid voltage signal under unbalanced and frequency variation condition. The single phase AANF provides high degree of accuracy than SRF-PLL and ANF in extracting appropriate signal information even for unbalanced and distorted grid condition. The important feature of the AANF is its amplitude adaptability, which improves its speed of response and accuracy when grid signal is of variable amplitude. Experimental results demonstrates better performance of AANF for frequency and amplitude detection than existing ANF and SRF-PLL, hence it can be used for wide range of applications such as converter interfaced distributed generation systems, islanding detection in smart grids, various fault detection techniques etc.

Adaptive notch filter based synchronization technique for integration of distributed generation systems to utility grid

This paper presents the adaptive notch filter based synchronization technique used for generation of reference currents for hysteresis current controlled three phase voltage source inverter. These three phase reference current components are then used to control the active power injected by the three phase voltage source inverter. In addition, the proposed control strategy can provide compensation for reactive power demands as well as harmonic load current requirements of the nonlinear loads during interconnection of inverter to the utility grid. Hysteresis current controlled technique is used to control the three phase voltage source inverter. By sensing the actual load currents, an adequate amount of active power, reactive power and harmonic current demanded by nonlinear load will be compensated with fast dynamic response into the utility grid. The effectiveness of the proposed technique is verified with injection of active and reactive power generated by three phase voltage source inverter through MATLAB/Simulink environment. An experimental work is undergoing and can be presented latter.

Soft switched coupled inductor based high step up converter for distributed energy resources

In this paper coupled inductor based high step up converter for dc micro grid is proposed. Switched capacitor based improved voltage extension cell is utilized to obtain high voltage gain. By using extended and improved voltage doubler cell, the voltage stress on the main switch and output diode are reduced. So active switches of low Rds(on) can be used and thus overall efficiency of the system is improved. Active clamp technique is incorporated to limit the voltage excursion on main switch and also to obtain zero voltage switching for both main and auxiliary switches which further improve the efficiency and power density. Design and analysis of the proposed converter is carried out and the result are verified by using PSIM Simulation package. Finally, a 500 W experimental prototype is build to verify the theoretical and simulation results.

Interleaved high step up converter for renewable energy sources

In this paper high step up two channel coupled inductor converter is proposed which can be used to interface low voltage renewable sources like solar photovoltaic, fuel cell system and energy storage elements like ultra-capacitors, battery etc. Interleaving technique reduces the output voltage ripple, current ripple and increases the power handling capacity. Leakage energy of the coupled inductors is effectively recycled to output using passive clamp technique which reduces the voltage stress on the active switches. So switches with low Rds(on) can be utilize to reduce the conduction losses and thus improves the efficiency. Design and analysis of a 500W interleaved coupled inductor dc-dc converter with switched capacitor is presented. To verify performance of proposed scheme, simulation in PSIM9.1 is carried out and the results are provided. Finally, the experimental results from a 500Wprototype are provided to validate the theoretical analysis and simulation results.

Grid Interfaced Distributed Generation System With Modified Current Control Loop Using Adaptive Synchronization Technique

This paper presents real-time implementation of a grid interfaced distributed generation (DG) system with modified current control loop using three phase amplitude adaptive notch filter (AANF) based synchronization tool. A grid current feedback based modified

Hybrid Control of High-Efficient Resonant Converter for Renewable Energy System

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Performance improvement of grid interfaced three level diode clamped inverter under various power quality events

-current control technique for interfacing inverter is developed in order to achieve constant loading on the grid, transient-free operation, and power factor improvement close to unity power factor (UPF) of the utility grid during sudden load variations. This technique does not require separate calculation of reference reactive component and harmonics component of currents hence reduces control circuit complexity. In addition, it requires only three voltage and three current sensors. Three phase AANF is developed and is used for online extraction of utility voltage phase angle to generate synchronized reference current signals for interfacing inverter. AANF is used because of its adjustable accuracy and amplitude adaptability even under unbalanced voltage sag and swell, frequency variation, and distorted grid conditions. Fast and accurate behavior of three phase AANF improves the dynamic response of entire DG system control performance for sudden load variations. The dynamic behavior of the proposed grid interfaced DG system is experimentally evaluated in maintaining constant loading on grid, transient-free operation, and power factor improvement close to UPF operation of the utility grid, by compensating total reactive power and harmonic current demanded by variable linear as well as nonlinear load.

Low switching stress DC-DC converter with capability of high voltage gain for low voltage energy sources

This paper presents the hybrid control of a dc–dc resonant converter for a dc micro-grid. The hybrid control is the simultaneous variation of the frequency and the duty ratio, which can provide excellent voltage regulation and maintain zero-voltage switching (ZVS) over a wide load range. Hence, excellent conversion efficiency is also maintained over the wide load range using hybrid control. However, the conventional control methods for a dc–dc resonant converter using either variable switching frequency or duty ratio have their own limitations. The frequency control requires wide variation in switching frequency for output voltage regulation, which leads to higher switching losses at turn-off of switches and lower efficiency particularly at light loads. The duty ratio control has a limitation of loosing of ZVS at light loads. The simulation and experimental results of hybrid control of resonant converter operating above 100 kHz with maximum duty ratio of 0.48 for 3 kW are presented from full load to no load. The maximum efficiency of the resonant converter is found to be 98%, which was achieved at 75% of the full load.