A random carrier frequency PWM technique with a narrowband for a grid-connected solar inverter

Abstract

The quality of power is always a concern for the high penetration of a grid-connected solar photovoltaic (PV) system due to the variation in solar irradiation and the temperature change of solar output, which in turn varies the fundamental component of power delivered to the grid. A solar source requires an inverter interface to supply the AC load as well as for the grid interconnection. Any reduction in the fundamental component generated by solar PV at a lower irradiation level or at hightemperature results in increasing %THD at the output of inverter for a given fixed switching frequency since harmonics due to PWM technique is comparable with the fundamental component. The selection of high-fixed-switching-frequency PWM reduces harmonics but increases the stress on switches and switching losses. It also suffers from issues of harmonics at carrier frequency and its sideband at multiples of switching frequency that causes acoustic noise and EMI. The random frequency PWM (Random PWM) method overcomes these issues presented by the fixed-frequency PWM method. However, a wide band of Random PWM makes the inverter filter design difficult and causes resonance in the distribution system. In addition, asymmetry in the carrier wave introduces even-order harmonics in the line current. Hence, this paper proposes a narrowband random frequency PWM method to reduce sideband harmonics, lower-order harmonics, even-order harmonics and a total harmonic distortion (THD) for a solar-based grid-connected inverter. Simulation results present a satisfactory performance of the proposed control technique for a steady-state and transient results. Experimental validation of the same is carried out on the OPAL-RT OP4500-based laboratory prototype of a 2-kVA inverter which depicts reduction in harmonics and hence improvement in power quality. KeywordsGrid-connected inverter • Harmonics • Linear control • Random PWM • Solar inverter B Rajendrasinh Jadeja

A Generalized Approach for Determining the Current Ripple RMS in Four-Leg Inverters with the Neutral Inductor

“…Small values of neutral inductors lead the four-leg inverter to approach the theoretical optimum (g → +∞) behavior exhibited by standard three-leg inverter [27,28]. Figures 2-5 validate general formulation (22) for all the common-mode injections listed in Table 1 in the cases of g = 0.25, g = 0.5, g = 1, and g = 2, respectively (i.e., L n = L/4, L n = L/2, L n = L, and L n = 2L). As is clearly visible in Figure 5, neutral inductor L n = 2L almost perfectly retraces conventional three-phase inverter behavior (indicated as "3-leg") due to its 98% convergence discussed above; similar considerations are visible in Figure 4 in the case of g = 1.…”

“…Good knowledge of converter harmonic pollution plays a crucial role during designing because of its influences on filtering stage sizing, switching frequency selection, efficiency estimation, and modulation scheme optimization [8,19,22]. Furthermore, the determination of current ripple RMS represents a key step in the calculation of popular figures of merit such as total harmonic distortion (THD) and total demand distortion (TDD), which are crucial for standard compliance [23,24].…”

A Discrete-Time Robust Adaptive PI Controller for Grid-Connected Voltage Source Converter with LCL Filter

“…Consider the plant described by (2)-(4), subject to assumptions A1 to A4, using the control law (12)- (14), and the adaptation algorithm (15)- (18), with limited reference, are able to find a parameters vector θ θ θ (k) whose limitation of parametric error vector φ φ φ (k) is ensured.…”

“…1.0053 Generally, VSC (Voltage Source Converters) are used to integrate the clean energy source to the electrical grid [12], with AC filters as interface. These filters are employed to reduce THD (Total Harmonic Distortion), produced by converter switching [13], once the quality of power is always a concern for the high penetration of grid-connected power systems [14]. It guarantees that power injection is in compliance with specific grid-connected standards [15], such as IEEE 1547 [16], standard for interconnecting distributed resources with electric power systems.…”

Variable Switching Frequency PWM for Three-Phase Four-Wire Split-Capacitor Inverter Performance Enhancement

“…Although in [7] four-leg inverters' switching losses and current ripple amplitude performances have been enhanced thanks to proper usage of DPWM, the harmonic spectrum preserves a narrowband cluster distribution. In [11], [12], RPWM is obtained by acting on the pulse disposition and switching frequency distribution, respectively. Thanks to the relevant harmonic spreading effect over the entire spectrum, it is possible to mitigate acoustic pollution [13] significantly.…”