In PV systems, DC-DC converters have been identified as one of the most critical and challenging sub-system in terms of failure rate. Thus, this paper proposes fault tolerant operation of a two-stage Buck/Buck-Boost converter under open-circuit switch failure. Remedial actions are efficient in any failure of one of the two switches of the converter. Here, a new unified approach is considered, for the overall fault tolerant operation of the two stages of the converter. The fault tolerant circuit we propose lies on performing redundancy by implementing the equivalent synchronous switch for the two main switches of the two stages, in offline mode. The fault tolerant circuit results from the basic two-stage Buck/Buck-Boost converter and its equivalent circuit with a synchronous switch, merged together to form the new DC-DC fault tolerant circuit. Therefore, post-fault operation at full power can also be performed. By using a switch fault management unit with reduced complexity, inserted between the control block and the switches, we have designed an unified, efficient and optimized fault tolerant control, suitable in both healthy and post-fault operations. Some selected simulation results and experimental tests, which all confirm the good performances of the proposed fault tolerant approach, are presented and discussed.

As an industry consumer of electric power, an electric arc furnace (EAF) is a major voltage flicker source that causes significant power-quality (PQ) problems. The fast response of the static synchronous compensator (STATCOM) makes it an efficient solution for improving PQ in distribution systems facing this kind of very nonlinear load. In this study, for voltage flicker mitigation of a 100-MVA EAF installed in Europe, a voltage-source-converter (VSC)-based STATCOM with high bandwidth is designed. The STATCOM's current reference includes both active and reactive current components. The performance of the STATCOM in voltage flicker mitigation is highly improved by applying this control strategy which uses the dc voltage margin of the VSC to provide for an active compensating current without oversizing the STATCOM converters capacitor. In this paper, first, the proposed STATCOM is studied through a generalized steady-state analysis. Second, the STATCOM's control strategies for voltage flicker mitigation are introduced and simulation results are provided and compared. Finally the complete model is validated by field tests over a 60-MVAr industrial STATCOM. Static and dynamic performance of the STATCOM is evaluated and voltage fluctuation mitigation studies are performed and discussed. The voltage flicker mitigation is evaluated through onsite measurements respecting international standards.

Energy harvesting has become a promising and alternative solution to conventional energy generation patterns to overcome the problem of supplying autonomous electrical systems. More particularly, thermal energy harvesting technologies have drawn a major interest in both research and industry. Thermoelectric Generators (TEGs) can be used in two different operating conditions, under constant temperature gradient or constant heat flow. The commonly used TEG electrical model, based on a voltage source in series with an electrical resistance, shows its limitations especially under constant heat flow conditions. Here, the analytical electrical modeling, taking into consideration the internal and contact thermal resistances of a TEG under constant temperature gradient and constant heat flow conditions, is first given. To give further insight into the electrical behavior of a TEG module in different operating conditions, we propose a new and original way of emulating the above analytical expressions with usual electronics components (voltage source, resistors, diode), whose values are determined with the TEG’s parameters. Note that such a TEG emulation is particularly suited when designing the electronic circuitry commonly associated to the TEG, to realize both Maximum Power Point Tracking and output voltage regulation. First, the proposed equivalent electrical circuits are validated through simulation with a SPICE environment in static operating conditions using only one value of either temperature gradient or heat flow. Then, they are also analyzed in dynamic operating conditions where both temperature gradient and heat flow are considered as time-varying functions.

Fault diagnosis in multilevel converters is of great importance since they are comprised of more solid-state switches, compared to the conventional two-level converters. This paper proposes a fast and efficient real time open-switch fault diagnosis, based on failure mode algorithm for a single-phase five-level neutral-point-clamped inverter. Component modeling and complicated calculations are avoided and load parameters are not required for realizing the proposed approach. Furthermore, the proposed strategy does not require any extra sensor. The signals already available in the control system such as the applied switching pattern and terminal voltage fulfill the fault diagnosis. Thanks to the proposed fault detection strategy, any misdiagnosis arising from noise existence, response time of the sensors, turn on and turn off delay times of the power switches and measurement errors is avoided. The simulations and experiments are carried out to confirm the performance and effectiveness of the presented strategy.

In this paper, a fast and efficient open-circuit switch and clamping diode fault diagnosis for Neutral-Point-Clamped inverters is proposed. Multilevel converters employed in safety-critical applications should include fault tolerant capability, where fault diagnosis plays a vital role. The proposed fault diagnosis algorithm is based on failure mode analysis, which is a logic based approach. The required signals and measurements are available in the healthy control system. Furthermore, component modeling, load parameters and complicated calculations are not required. The fault detection and identification of the faulty switch or clamping diode are carried out based on the available data such as switching pattern and terminal voltage. Although switches are more fragile than clamping diodes, clamping diodes are also subjected to breakdown. Hence, it is also crucial to achieve a clamping diode fault diagnosis strategy. Moreover, for fault detection procedure, a voltage quantifier is proposed to avoid any misdiagnosis arising from measurement errors and voltage drop in the circuit. The simulation and experimental results are presented to validate the effectiveness of the proposed approach.