This paper presents a comparative study of discrete proportional integral (PI) and proportional resonant (PR) current control for single-phase uninterruptible power supply (UPS) inverters. There is an increasing requirement for current and voltage-controlled UPS inverters with very low or zero steady-state error, improved transient response and lower total harmonic distortion (THD). The most promising type of current regulator for single-phase inverters is PR control because it can introduce an infinite gain at a selected resonance frequency such as the fundamental frequency to eliminate the steady-state error, which cannot be achieved by well-known proportional integral (PI) control. Note that PI control has limitations in terms of the steady-state magnitude and phase errors. In addition, PI control also has limited harmonic rejection capability, unlike the PR control, also can compensate for low-order harmonics. Imperfections in the current and voltage control scheme results in higher harmonic distortion of the output current and voltage. In this paper, performance of PR control parameters (Kp, Ki, and ωc) and filter parameters (Lf and Cf) are optimally tuned to obtain a very low current THD with reduced output voltage ripple and steady-state error. The analysis, design and implementation of both PI and PR current control in single-phase UPS inverter applications through simulations and experiments are also presented in this paper. The performance of both of these control schemes are analyzed in terms of steady-state response, transient response, and level of current harmonics.

This article presents a three-phase hybrid multilevel inverter (MLI) with enhanced pulsewidth modulation (PWM) strategy. The proposed hybrid MLI is developed based on the series connection of half-bridge and full-bridge for its level generation together with the T-type inverter for its polarity generation. The level and polarity generation circuits operate at high and fundamental frequencies respectively. An enhanced PWM strategy has been proposed to reduce the computational complexity and solve the high-frequency switching transitions issue in the existing hybrid MLI modulation method. The proposed MLI can produce 11 levels of line output voltage with reduced dc sources requirement. The detailed analyses which have been performed include the circuit configuration, operating principles and modeling, PWM signals generation, output voltage characteristics, dynamic response, harmonics content, power loss analysis and voltage stress of power switches. The results obtained from simulation and experiments verified the operating principle and functionality of the proposed hybrid MLI.

This paper presents the design and analysis of a three‐level hybrid boost converter based on a single‐phase three‐level T‐type inverter. The proposed converter can provide high energy conversion efficiency and high voltage gain capability with reduced component count. The pulse‐width‐modulation signals of the proposed converter are generated by comparing two duty cycles and two triangular carrier signals. The proposed converter consists of four power switches, four diodes, an inductor, and two capacitors. Detailed converter operations at each switching state with the corresponding voltage and current waveforms of each component are discussed. The functionality and performance of the proposed converter are verified through simulation and experimental results.

In this paper, photovoltaic (PV) string failure analysis and health monitoring of PV modules based on a low-cost self-powered wireless sensor network (WSN) are presented. Simple and effective fault detection and diagnosis method based on the real-time operating voltage of PV modules is proposed. The proposed method is verified using the developed health monitoring system which is installed in a grid-connected PV system. Each of the PV modules is monitored via WSN to detect any individual faulty module. The analysis of PV string failure includes several electrical fault scenarios and their impact on the PV string characteristics. The results show that a degraded or faulty module exhibits low operating voltage as compared to the normal module. The developed health monitoring system also includes a graphical user interface (GUI) program which graphically displays the real-time operating voltage of each module with colors and thus helping users to identify the faulty modules easily. The faulty modules identification approach is further validated using the PV module electroluminescence (EL) imaging system.

This paper presents the analysis of current harmonics compensation using the proportional-resonant controller for single-phase stand-alone photovoltaic inverter applications. The effect of frequency variation in the reference signal to the controller performance was also analyzed. The controller parameters (K_p , K_i , and ω_c ) and the inductor-capacitor (LC)-filter parameters are optimally selected to obtain a very low current total harmonic distortion . The control algorithm was implemented using a low-cost digital signal processor (DSP) TMS320F28335 eZdsp development board. Both simulation and experimental results validate the performance and the effectiveness of the control technique used.