Intermittent changes in irradiance caused by passing clouds inevitably lead to fluctuations in photovoltaic (PV) power generation. To ensure the stability of a power grid with integrated solar PV generation, a battery energy storage system (BESS) is an intrinsic solution to effectively process the PV power before transmitting it into the grid. Alternatively, a PV software-based ramp rate (RR) control can be applied to mitigate the PV power fluctuations without any BESS, which is known to be cost-effective. The contribution of this paper is to compare various BESS-based and cost-effective software-based RR control strategies operating with real-time measured information, and analyze their effectiveness in regulating the PV power fluctuations. Furthermore, this paper studies the BESS utilization behavior among hardware-based control strategies, and also provides insights into which strategy is more appropriate for specific applications. The investigations are carried out through simulation case studies with a real-field one-day fluctuated irradiance profile.

In this paper, the effect of min-max zero-sequence voltage (ZSV) injection on the maximum average neutral-point (NP) current control limits of a neutral-point-clamped (NPC) converter is analyzed. These current limits determine the stable operating range of the NPC converter in applications that impose a nonzero average NP current, like- NPC converters feeding multiterminal dc loads, back-to-back-connected NPC converter-based wind and high voltage dc transmission systems, etc. Previously, a dual-mode modulation technique was implemented in the literature which provided the maximum average NP current limits without considering the ZSV effect. As the ZSV injection affects the NP duty cycles, and in turn the NP current, it is necessary to analyze and quantify its effect. In this paper, the effect of ZSV on the current limits is analytically calculated. Simulation results are obtained in MATLAB/Simulink environment to validate the derived analytical equations.

Photovoltaic (PV) grid support functionality (frequency support) can be accomplished with the aid of flexible power point tracking (FPPT) technology. However, the convergence rate of FPPT algorithms needs to be fast, to provide grid support under transients. To fulfil this purpose, a Newton’s method-based (NM-B) FPPT algorithm is proposed in this paper that offers quadratic convergence, which is a higher convergence rate compared to the existing methods. Moreover, the search algorithm requires only a single initialization point, thus eliminating the difficulty of setting up the search boundary as in the case of the binary search-based and secant method-based (SM-B) FPPT algorithms. Simulation validation is performed for the proposed NM-B FPPT algorithm and the results are compared with the SM-B FPPT algorithm.

The neutral-point-clamped (NPC) converter employed in applications like bipolar dc-bus, back-to-back converters, power compensator, etc., requires a nonzero average neutral-point (NP) current injection under certain operating conditions. In order to better implement the average NP current injection, this paper studies the maximum and minimum average NP current that can be injected with an NPC converter. For this study, a three-level modulation technique is employed in which one of the three phases is selected to switch between the positive dc-rail and the negative dc-rail while the other two phases switch in two consecutive voltage levels. The maximum and minimum average NP current injection limits are analyzed under different loading conditions. The presented study also evaluates the effects of modulation index and operating power factor on the limits.

In this paper, a vector-based synchronization technique is proposed for the synchronization of a solar photovoltaic (PV)-battery system to the grid. In this technique, the three-phase grid and point of common coupling voltages are transformed into two vectors in the α-β plane. Due to the absence of a phase-locked loop and feedback, the proposed technique is simple, and also instantaneous changes in the voltages are considered here. The grid-connected solar PV-battery system operates in the current control mode, while the islanded system operates in a voltage control. Experimental results are obtained on a grid-solar PV-battery system in grid-connected and islanded modes. The two transitions between these operating modes are also studied in detail. All these test results of harmonics in grid voltages and currents are found satisfactory and in accordance to the IEEE-519 and 1547 Standards.