A systematic framework for reliability assessment and fault-tolerant design of multiphase dc-dc converters deployed in photovoltaic applications is presented. System-level steady-state models allow a detailed specification of component failure rates, and in turn establish the effects of ambient conditions and converter design on reliability. Markov reliability models are derived to estimate the mean time to system failure. Case studies applied to two- and three-phase, 250-W converters demonstrate that topological redundancy does not necessarily translate to improved reliability for all choices of switching frequency and capacitance. Capacitor voltage rating is found to be the dominant factor that affects system reliability.

A Unified Approach to Reliability Assessment of Multiphase DC–DC Converters in Photovoltaic Energy Conversion Systems

Electric power quality (PQ) in distribution system has become increasingly significant subject both for end users and power suppliers with the deregulation of the electric power market. The inadequate performance of conventional compensation devices to mitigate PQ problems has revealed the use of advanced power electronics based compensation devices. Distribution static synchronous compensator (DSTATCOM) is one of the shunt connected custom power devices used to improve PQ, voltage and reactive power support and to increase the capability of the auxiliary service for utility grid. This study presents a comprehensive review of the various DSTATCOM configurations for single-phase (two-wire) and three-phase (three or four-wire) systems and control strategies for the compensation of different PQ problems in distribution systems. In addition, comprehensive explanation, comparison and discussion on DSTATCOM technology are performed. Furthermore, latest trends, practical consideration and some future research fields on DSTATCOMs are discussed in detail. This is intended to present a broad perspective on the status of DSTATCOM technology to researchers dealing with compensation of PQ problems in distribution systems.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-pel.2014.0531

Mitigation of power quality problems using distribution static synchronous compensator: a comprehensive review

For three-phase interleaved boost converters (IBC), the master-slave current balancing control is often used to cooperate with the voltage regulation control, but the tuning of the current balancing controller would have effect on the voltage regulation loop. In this letter, the decoupled master-slave current balancing control is proposed, and its small-signal transfer functions show that the voltage regulation loop and the current balancing loop are decoupled. A 300 W prototype of IBC is implemented to demonstrate the proposed control method.

Decoupled Master-Slave Current Balancing Control for Three-Phase Interleaved Boost Converters

Inductor current measurements using only a single dc link current sensor in an interleaved dc-dc converter is introduced in this paper. This technique is appealing for the interleaved dc-dc converter because it minimizes the number of current sensors, thereby reducing sensor cost, weight, and volume. A combination of analytical and experimental results is provided to confirm that the single dc link current sensor technique is capable of achieving attractive performance characteristics in the areas of inductor current reconstruction, inductor current regulation, and output voltage regulation for the interleaved dc-dc converter.

Inductor Current Measurement and Regulation Using a Single DC Link Current Sensor for Interleaved DC–DC Converters

The partially shaded photovoltaic (PSPV) condition reduces the generated power and contributes to hot spot problems that may lead to breakdown of shaded modules. PSPV generates multiple peak, one global one and many other local peaks. Many efficient, accurate and reliable maximum power point tracker (MPPT) techniques are used to track the global peak instead of local peaks. The proposed technique is not limited to global peak tracking, but rather it is capable of tracking the sum of all peaks of the PV arrays using an interleaved boost converter (IBC). The proposed converter has been compared with the state of the art conventional control method that uses a conventional boost converter (CBC). The converters used in the two PSPV systems are interfaced with electric utility using a three-phase inverter. The simulation findings prove superiority of the PSPV with IBC compared to the one using CBC in terms of power quality, reliability, mismatch power loss, DC-link voltage stability, efficiency and flexibility. Also, IBC alleviates partial shading effects and extracts higher power compared to the one using CBC. The results have shown a remarkable increase in output generated power of a PSPV system for the three presented scenarios of partial shading by 61.6%, 30.3% and 13%, respectively, when CBC is replaced by IBC.

Maximum Power Extraction from a Partially Shaded PV System Using an Interleaved Boost Converter

In the present paper, an application of interleaved dc-dc converter in photovoltaic (PV) modular system has been presented. In the multi-string technology, several PV strings are interfaced with their own dc-dc converter to a common dc-ac inverter. Enlargements are easily achieved since a new string with dc-dc converter can be plugged into the existing platform. This paper proposes a simple method to connect various PV modules in order to improve power quality. Thanks to the proposed digital control method, the PV interleaving becomes simple and efficient in terms of dynamic performances, steady-state condition and well regulated output voltage.

Interleaved dc-dc Converters for Photovoltaic Modules

In this paper a new DC line current compensator is presented. The proposed converter is able to compensate very low amplitude current harmonics and is very useful in railway applications where harmonic pollution can produce interference in the signaling systems over DC lines. The active compensator is modular and composed by multiple cells connected in series and controlled in order to minimize the modulation current ripple. Moreover a design criteria are shown and simulation results demonstrate the effectiveness of the proposed solution.

Multilevel harmonics current active compensator for DC feeding line

Deregulation and liberalization of international energy market are recently increasing the demand, in transmission and distribution networks, for more efficient solutions for Power Management and better Power Quality. Fast and reliable VAr control systems, such as STATCOMs, enhance the dynamic stability of power networks. Rongxin Power Electronic Co (RXPE) developed a transformerless Cascaded H-Bridge Multilevel converter, to be directly connected to 35 kV grid. After an overview of STATCOM topologies and semiconductor devices (section I and II), Some test results in factory is introduced.

35kV/±200Mvar transformerless STATCOM based on Cascaded H-Bridge Multilevel converter

In this paper a stability analysis method for unbalance compensation system based on AC-Chopper is proposed. Employing Ac-Choppers and Steinmetz theory it's possible to obtain a dynamic compensation system. This system's performance and stability are not depending only on the cause of unbalance but also on grid parameters such as line impedances and other connected loads. If a quasi-static sinusoidal steady-state approximation is hypothesized, through the multivariable control theory it's possible to study the compensation system stability propriety in relation with grid parameters.

/pdf/analysis-of-a-closed-loop-control-for-current-unbalance-196chvouo5.pdf

G. Torre

Papers

Interleaved dc-dc Converters for Photovoltaic Modules

Multilevel harmonics current active compensator for DC feeding line

35kV/±200Mvar transformerless STATCOM based on Cascaded H-Bridge Multilevel converter

Analysis of a closed loop control for current unbalance compensation based on Ac/Ac converters