Search

Summary: In this work, an isolated modular resonant circuit with effective voltage regulation is presented as front‐end for multilevel inverter system to interface renewable sources of energy with micro grid. Inputs of each module of the converter are connected to low‐voltage DC sources. Modular‐structured module outputs may be linked in sequence or parallel to attain the desired DC link capacitor voltage for multilevel inverter. The proposed converter overcomes imbalance in the capacitor voltage of diode‐clamped inverter structure. Interleaved phase shift of 90° is supplied among the gate pulses of all four modules that minimizes the input‐side current ripples. An effective zero voltage switching (ZVS) is achieved over wide load range using duty cycle and frequency‐duty cycle double control method to improve system performance at light load condition. Adopting powder core magnetics and low forward voltage insulated‐gate bipolar transistors (IGBTs) reduces magnetic and conduction loss. A 12‐kW prototype of the designed modular resonant converter was verified by experimentation with a different‐level diode‐clamped inverter structures. [ABSTRACT FROM AUTHOR]

An optimized resonant converter with zero-voltage switching over an extensive range of loading is proposed to integrate renewable energy sources to an onboard charger. In conventional resonant circuit, high-frequency transformer (HF) parasitic components are used as tank circuit, this degrades the performance due to non-optimal magnetic components. Here, the HF transformer is fabricated with optimized resonant tank circuit shunt branch inductance ($L_p$) as magnetizing inductance, hence eliminating the need for shunt branch inductance. The proposed resonant converter circuit design is optimized for minimum kilovoltampere rating and better voltage regulation with both duty cycle and frequency control (mixed control method). Furthermore, the performance of the converter at a very light load is improved using the proposed control method. Incorporating a low- $R_{\text{DS}}(\text{ON})$ silicon carbide mosfet and softly turning off the switches for a wide load variation minimizes conduction and switching losses and improves efficiency. Using powder core for the design of the tank circuit reduces magnetic losses. A 3-kW prototype of the converter is built to verify the performance from no load to full load. The highest efficiency of the proposed converter is 98.6%, attained at 50% full load. [ABSTRACT FROM AUTHOR]

This paper presents a reliable microgrid for residential community with modified control techniques to achieve enhanced operation during grid connected, islanded, and resynchronization mode. The proposed microgrid is a combination of solar photovoltaic, battery storage system and locally distributed generation (DG) systems with residential local loads. A modified power control technique is developed such that local load reactive power demand, harmonic currents, and load unbalance are compensated by respective residential local DG. However, active power demand of all local residential load is shared between the microgrid and respective local DG. This control technique also achieves constant active power loading on the microgrid by supporting additional active power local load demand of respective residential DG. Hence, proposed modified power control technique achieves transient free operation of the microgrid during residential load disturbances. An additional modified control technique is also developed to achieve seamless transition of microgrid between grid-connected mode and islanded mode. The dynamic performance of this microgrid during grid-connected, islanded, and resynchronization mode under linear and nonlinear load variations is verified using real-time simulator. [ABSTRACT FROM AUTHOR]

This paper presents a modified cascaded multi-level structure for high voltage application. The topology proposed optimizes switch count per voltage level along with the reduction in voltage stress across the switches. Optimization based on different criteria has been discussed and a comparison of the proposed structure with existing topology has been carried out. This paper also shows a level shift PWM control scheme and a closed loop multi-band hysteresis control scheme. The topology is simulated for the above two control schemes on MATLAB and also verified experimentally for single phase seven-level inverter. The experimental verification was done with DSP F28337D TI Launchpad on series resistance and inductance (RL) load. [ABSTRACT FROM AUTHOR]

A two-stage grid-tied efficient solar photovoltaic (SPV) system with zero voltage switching (ZVS) and zero current switching (ZCS) at the dc–dc converter stage and adaptive synchronization at the inverter stage is proposed. In the first stage, an improved high step-up boost-integrated flyback converter with quasi resonant voltage multiplier cell is proposed. ZVS turn-on of all mosfets and ZCS turn-off of all diodes of resonant voltage multiplier cell results in high efficient power conversion compared with the conventional boost-integrated flyback converters. Small-sized coupled inductor enhances magnetic utilization in this converter. Second stage consists of a single-phase H-bridge grid interfaced inverter with variable band hysteresis current control technique. Amplitude adaptive notch filter is used to extract fundamental unit voltage vector of grid voltage required for estimation of synchronized reference current for hysteresis controller. A 250 W laboratory prototype is developed and experimentally evaluated. Experimental results demonstrate efficient renewable energy conversion at dc–dc converter stage and quality power injection at dc–ac inverter stage of the proposed grid-tied SPV system under changing solar insulation levels. [ABSTRACT FROM PUBLISHER]

This paper presents real time performance evaluation of three phase extension of an amplitude adaptive notch filter (AANF) for online estimation of frequency, amplitude, and sequence components of the input grid voltage signal. The performance of an extended AANF is compared with conventional synchronous reference frame-phase lock loop (SRF-PLL), enhanced phase lock loop (EPLL), and existing adaptive notch filter (ANF). Comparative analysis has been carried out based on their ability in extracting frequency and amplitude of input grid voltage signal under balanced and unbalanced voltage sag/swell, frequency shift and distorted grid condition. Three phase AANF method provides high degree of accuracy than SRF-PLL, EPLL, and ANF in extracting appropriate signal information for unbalanced and harmonically distorted grid condition. The important feature of this method is its amplitude adaptability, which improves its speed of response and accuracy when grid signal is of variable amplitude. OPAL-RT’s (OP4500) real time controller with an in-built Xilinx Kintex-7 FPGA processor is used for real time implementation. Experimental results validate fast and accurate performance of an extended AANF in extracting frequency, amplitude, and sequence components of the utility grid voltage signal, which can be further used for performance improvement of grid connected renewable energy systems, custom power devices, and flexible ac transmission systems (FACTS) devices. [ABSTRACT FROM PUBLISHER]

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 $dq$-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. [ABSTRACT FROM PUBLISHER]

This paper proposes a modified control scheme for a grid connected microgrid, which is contrived by integrating multiple nanogrids. In the considered system, each nanogrid consists of a generation unit from solar photovoltaic (PV) along with battery energy storage (BES) system and local loads. The nanogrid has the flexibility to operate in microgrid connected mode or islanded operating mode. Similarly, the microgrid can also be operated in grid connected mode or islanded mode. To achieve appropriate load sharing between different nanogrids considering local load demands and source power availability, a modified control scheme is developed. The proposed scheme compensates for the required reactive power, harmonics and unbalanced currents locally which are demanded by the local loads in nanogrids in order to improve the power quality in the microgrid. The smooth transition between the modes of operation of nanogrids and microgrid is achieved with the proposed modified control scheme. In addition, the proposed modified control scheme allows the microgrid and main grid to remain free from transients generated by load disturbances in nanogrid and disturbances in the microgrid respectively. Therefore, the effect of disturbances on voltage and frequency of the microgrid is reduced. A simple control scheme is developed to address the challenging issues for smooth operation of the microgrid such as active power sharing among the sources based on their ratings, power quality enhancement (compensation of harmonic components, unbalanced current and reactive power) and seamless transition between the modes of operation (during islanding from grid and re-synchronisation with grid). The performance of the proposed modified control scheme is verified in a real time simulator during variable loading conditions. [ABSTRACT FROM AUTHOR]