A hybrid cascaded multilevel inverter application for renewable energy resources including a reconfiguration technique

Abstract

A hybrid cascaded multilevel inverter application for renewable energy resources including a reconfiguration technique is developed. The objective of this research is to propose an alternative topology of hybrid cascaded multilevel inverter applied to a low voltage dc microgrid in telecommunication buildings. The modified PWM technique is also developed to reduce switching losses. Also, the proposed topology can reduce the number of required power switches compared to a traditional cascaded multilevel inverter. A possible reconfiguration technique after faulty condition is also discussed. PSIM (PowerSim) and Simulink/MATLAB are used to simulate the circuit operation and control signal. A 3-kW prototype is developed. The switching losses of the proposed multilevel inverter are also investigated. By using the modified PWM technique and reconfiguration method, the proposed hybrid inverter can improve system efficiency and reliability. The proposed inverter efficiency is 97% under tested condition. The results show that proposed hybrid inverter topology is a promising method for a low voltage dc microgrid interfacing with renewable energy resources.

Reconfiguration of NPC Multilevel Inverters to Mitigate Short Circuit Faults Using Back-to-Back Switches

“…Due to the particularity of flying capacitor MLIs, a control-strategy-based reconfiguration method with minimum add-on component was proposed in [33], the same output voltage levels are achieved with subtraction of capacitor voltage in post-fault condition. For three-phase systems, when one device fails, the corresponding phase leg also fails and may cause unbalanced voltages and currents among phases; a neutral-shifted method was developed to handle the unbalanced condition [30], [34], [35]. These control-strategy-based reconfiguration methods are designed for different topologies and can reduce the complexity and cost of MLIs significantly.…”

“…This could cause significant degradation of voltage quality when phase voltage is of interest for grid-tied application, per-phase analysis, modeling, etc. Similar conditions of distorted phase-to-neu- tral voltage happen with the neutral point shift (NPS) method [30], [34], [35].…”

“…The peak value of output voltage is also reduced significantly [22]. The NPS method achieves a decreased level condition in the failed phase leg without any additional components [30], [34], [35]. However, it also reduces the RMS value of the phase voltage and it is more applicable to open circuit faults of MLIs that contain unit cells.…”

“…The method of modifying the reference signal (MRS) [32] does not require add-on components and is easy to achieve, but it causes reduced output voltage peak and unbalanced per-phase condition. The NPS method [30], [34], [35] also has the drawback of reduced output voltage peak. TABLE IV summarizes the drawbacks of the existing reconfiguration methods and compares these methods with the proposed method.…”

Introduction to Multilevel Converters

“…This implementation reduces the required number of separate DC sources. Figure 10.24 [4] shows one branch of the In this way, we get a 9-level inverter with only two separate DC sources per phase, or a total of six separate sources for the whole three-phase inverter. For the realization of the same inverter with a standard H-bridge inverter modules, 16 separate DC sources are needed.…”