A Shadow Tolerant Configuration for PV Integration to Grid using Modular Multilevel Converter

A shadow-tolerant photovoltaic converter configuration using the modular multilevel converter and the differential power processing converter without compromising the efficiency of the overall system is presented in this work. The proposed configuration is able to extract maximum power from the unshaded panels in the photovoltaic string under partially shaded condition, therefore, increasing the overall energy yield. A method to eliminate capacitor voltage ripple on the unshaded PV module is presented. This further improves the efficiency of energy collection by mitigating the effects of voltage ripple around the maximum operating point.</p

Integrating battery into MMC submodule using passive technique

The modular structure and the many other advantages of the Modular Multilevel Converter makes it an attractive converter for Battery Energy Storage Systems, allowing the battery units to be distributed throughout the convert, connected in each submodule. However, such an arrangement results in large oscillating components in the battery current, which is harmful to battery performance and lifetime. In most literature this is solved using DC-DC converters as active interfaces between battery and submodule. This paper investigates a passive filter arrangement as an alternative solution to the DC-DC converters. Where the batteries are interfaced with the submodules using a passive filter that suppresses the fundamental component and control technique that injects circulating current to suppress second harmonic component. It is concluded that this passive technique could be an attractive solution especially where high reliability is of concern

Modular multilevel converter for photovoltaic application with high energy yield under uneven irradiance

The direct integration of Photovoltaic (PV) to the three-phase Modular Multilevel Converter (MMC) without dc–dc converters results in high-efficiency PV power plant with increased energy yield. The arm power control method for the MMC further improves the extraction of available power under uneven irradiance across different phases of the MMC. However, the uneven irradiance between the sub-modules results in residual voltage that results in harmonics and unbalance components. In this paper, the effect of uneven irradiance across the sub-module of the MMC is investigated with arm power control method. A modified balancing algorithm for the arm power control of the MMC is proposed which enables balanced power to be injected into ac grid despite uneven irradiance across the sub-modules in the MMC. The modified balancing algorithm enables to keep the unbalance in the phase currents below 10% and the Total Harmonic Distortion (THD) is confined as per IEEE 519 standard

Frequency Adaptive Digital Filter Implementation of Proportional-Resonant Controller for Inverter Applications

The Proportional-Resonant control is used in control schemes that directly act on AC variables avoiding synchronous frame transformation. In this paper, the PR controller is realized using an IIR digital filter and implemented using direct form II transposed structure. It has a simpler discrete time implementation, however, the disadvantage of being difficult to make them frequency adaptive, i.e. change the filter's resonant frequency. Simple closed loop expressions are derived for the coefficients in terms of resonant frequency, sampling time and damping factor. Based on this, a frequency adaptive proportional-resonant controller is proposed. It is shown that by modifying a single coefficient in the IIR realization, the controller adapts its resonant frequency to grid frequency fluctuation resulting in a simple and efficient frequency-adaptive proportional-resonant controller.</p

Modular Multilevel Converter for Photovoltaic Application with High Energy Yield under Uneven Irradiance

The direct integration of Photovoltaic (PV) to the three-phase Modular Multilevel Converter (MMC) without dc-dc converters results in high-efficiency PV power plant with increased energy yield. The arm power control method for the MMC further improves the extraction of available power under uneven irradiance across different phases of the MMC. However, the uneven irradiance between the sub-modules results in residual voltage that results in harmonics and unbalance components. In this paper, the effect of uneven irradiance across the sub-module of the MMC is investigated with arm power control method. A modified balancing algorithm for the arm power control of the MMC is proposed which enables balanced power to be injected into ac grid despite uneven irradiance across the sub-modules in the MMC. The modified balancing algorithm enables to keep the unbalance in the phase currents below 10% and the Total Harmonic Distortion (THD) is confined as per IEEE 519 standard.</p