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Variable switching frequency pulse width modulation (VSF PWM) has been proposed in the past to optimize the total harmonic distortion (THD) performance and switching losses of an inverter. Nevertheless, such VSF PWMs give rise to switching harmonics which vary across a wide frequency spectrum, where the lower frequencies could resonate with the filter while the upper frequency could exceed the maximum switching frequency. This complicates VSF PWM design, restricting their practical uses. In this paper, a confined band VSF PWM (CB-VSF PWM) for a single-phase inverter with an LCL filter is presented. By confining the switching frequencies within a practical band, the design of the filter becomes easier while maintaining low current THD with low switching losses. The choices of the upper and lower bands of the proposed VSF are defined and the design criterion is introduced. It is found that the proposed method allows reduction in switching losses as well as reduction in current THD when the effect of the LCL filter is taken into consideration. The performance analysis is validated through simulation and experimental results in a 1 kW inverter. [ABSTRACT FROM AUTHOR]

Microgrid coordinated controllers are designed so as to optimize the utilization of energy available in existing energy storage system (ESS) as well as the energy being generated from prevailing renewable energy sources (RES). If there is a surplus in the generated renewable energy, it will be used to charge the ESS if their capacity permits, otherwise, the surplus energy is curtailed. However, during a grid loss, i.e. during unintentional islanding, the surplus energy can lead to an increase in the DC link voltages feeding the DC-AC inverters, which may subsequently trip them off. Clearly, this has an adverse effect on the reliability of the microgrid. In this paper, a new strategy of microgrid control is proposed for enhancing the microgrid reliability by protecting it against unintentional islanding instability. In this strategy, the DC link voltage is used as a feedback parameter in the droop control loop. This bounds the DC link voltages and consequently leads to reliable operation. The validity of the proposed control scheme was verified by software simulations using MATLAB/Simulink. [ABSTRACT FROM AUTHOR]

This paper presents a fuzzy logic controller (FLC)-based single-ended primary-inductor converter (SEPIC) for maximum power point tracking (MPPT) operation of a photovoltaic (PV) system. The FLC proposed presents that the convergent distribution of the membership function offers faster response than the symmetrically distributed membership functions. The fuzzy controller for the SEPIC MPPT scheme shows high precision in current transition and keeps the voltage without any changes, in the variable-load case, represented in small steady-state error and small overshoot. The proposed scheme ensures optimal use of PV array and proves its efficacy in variable load conditions, unity, and lagging power factor at the inverter output (load) side. The real-time implementation of the MPPT SEPIC converter is done by a digital signal processor (DSP), i.e., TMS320F28335. The performance of the converter is tested in both simulation and experiment at different operating conditions. The performance of the proposed FLC-based MPPT operation of SEPIC converter is compared to that of the conventional proportional–integral (PI)-based SEPIC converter. The results show that the proposed FLC-based MPPT scheme for SEPIC can accurately track the reference signal and transfer power around 4.8% more than the conventional PI-based system. [ABSTRACT FROM AUTHOR]