Discrete Model-Predictive-Control-Based Maximum Power Point Tracking for PV Systems:Overview and Evaluation

The main objective of this work is to provide an overview and evaluation of discrete model-predictive control (MPC)-based maximum power point tracking (MPPT) for photovoltaic systems. A large number of MPC-based MPPT methods have been recently introduced in the literature with very promising performance; however, an in-depth investigation and comparison of these methods has not been carried out yet. Therefore, this paper has set out to provide an in-depth analysis and evaluation of MPC-based MPPT methods applied to various common power converter topologies. The performance of MPC-based MPPT is directly linked with the converter topology, and it is also affected by the accurate determination of the converter parameters; sensitivity to converter parameter variations is also investigated. The static and dynamic performance of the trackers is assessed according to the EN 50530 standard, using detailed simulation models, and validated by experimental tests. The analysis in this work aims to present useful insight for practicing engineers and academic researchers when selecting the maximum power point tracker for their application.</p

Performance Comparison of Phase Shifted PWM and Sorting Method for Modular Multilevel Converters

Modular Multilevel Converters (MMC) are the solution of preference in HVDC applications due to modularity, scalability, low losses and low filtering requirement. Carrier-based (PWM) and carrier-less (nearest level control) modulation can be applied. By using advanced sorting methods focusing on keeping the capacitor voltage ripple under some limit, unnecessary switching events are eliminated leading to reduced switching losses. This paper presents a comparison between the steady-state performances in terms of output voltage THD and equivalent switching frequency of the Phase Shifted Carrier PWM and NLC plus sorting methods

Control of Modular Multilevel Converter with reduced internal data exchange

Modularmultilevel converters (MMC) are penetrating due to their superior performances. Due to the modular structure of the converter, communication platform has to be established between the submodules (SMs) and a central controller unit (CCU). When the communication platform is designed for such an application, several key parameters have to be considered such as high-speed data transfer with low propagation delay, data integrity, and ability for accurate synchronization. In order to minimize the data flow in the MMC, a hierarchical control is proposed where a CCU calculates an identical reference for all the SMs, while the modulation and capacitor voltage balancing is performed in the controller from the SM. Thus, at each sampling instance, only four bytes references are sent by the central controller to the controllers from the SM, while one or two bytes are received from SMs. Furthermore, the control algorithm is validated through experiments

Three-Phase Photovoltaic Systems:Structures, Topologies, and Control

Photovoltaic (PV) technology has experienced an unprecedented growth in the last two decades, transforming from mainly an off-grid niche generation to a major renewable energy technology, reaching approximately 227 GW of capacity worldwide at the end of 2015 with a predicted extra 50 GW of new installations for 2016 [1]. Large PV power plants interfacing the grid through a three-phase power electronic converter are now well on the way to become a major player in the power system in many countries. Therefore, this chapter gives an overview of PV systems with a focus on three-phase applications from a hardware point of view, detailing the different PV inverter structures and topologies and discussing the different control layers within a grid-connected PV plant. Modulation schemes for various PV inverter topologies, grid synchronization, current control, active and reactive power control, maximum power point tracking, and grid integration requirements and support functions are also reviewed.</p

FPGA-based implementation of sorting networks in MMC applications

In this paper an implementation technique for Field Programmable Gate Array (FPGA) devices of two Sorting Networks (SNs) used for control of Modular Multilevel Converter (MMC) is presented. In such applications, the classical sorting algorithms are based on repetitive/recursive loops, and they are usually implemented in microcontrollers or DSPs. However, they are not convenient for hardware implementation due to their inherent sequential operation. Instead, the proposed SNs, are suitable for FPGA devices thanks to their fixed parallel structure that allows improving the timing performance of the capacitor voltage balancing algorithm. The advantages and the main challenges of the Bitonic SN and Even-Odd SN in MMC applications are discussed. Moreover, in order to pre-evaluate the required resources and the execution time, equations are derived for both the proposed SNs and then a comparison is performed between them. The proposed equations are validated by comparing the real required resources with the estimated ones by using the Xilinx Vivado Design Suite tool. Finally, the operation of the proposed Bitonic SN is also tested in Vivado Simulator, achieving the sorted list of 8 elements in 18 clock cycles as expected

Resonance reduction for AC drives with small capacitance in the DC link

Pulse-width modulated ac drives equipped with a small dc-link capacitor are becoming an attractive solution for electric drive applications with moderate requirements for shaft dynamic performance. However, when these drives are fed from a weak grid, a resonance between the line side impedance and the dc-link capacitor appears. Due to this resonance, the total harmonic distortion and the partially weighted harmonic distortion of the line currents are increased, which may raise compatibility problems with the ac line harmonic standards. This paper proposes a novel dc-link voltage compensation method, which can reduce the amplitude of the aforementioned oscillation, while the large dc-link voltage variation, caused by the rectification, can be eliminated from the motor current. The method has been experimentally validated and the results show excellent performance.</p