Cascaded Transformer Multilevel Inverter Research Articles

Dead-Time Compensation Based on Current Phase Estimation for High-Frequency Cascaded Transformer Multilevel Inverter

Dead-Time Compensation Based on Current Phase Estimation for High-Frequency Cascaded Transformer Multilevel Inverter

Energy Balancing With Wide Range of Operation in the Isolated Multi-Modular Converter

The series-connection of modules in multilevel converters are prone to energy imbalances in the dc capacitor due to the differences between the power absorbed and consumed. In renewable energy applications where the primary source is directly connected to each module, energy imbalances can be even worse if the primary sources are affected by unpredictable weather conditions. Therefore, control strategies are required to compensate such energy imbalances, while maintaining the correct converter operation. Focusing our attention on a cascaded transformer multilevel inverter called Isolated Multi-Modular Converter, this paper introduces the combination of two control strategies aimed at providing a wide range of operation under imbalanced energy states. A general analytical model, including the regulation capability and differences with an existing strategy are presented to demonstrate the performance of the control proposed. The effectiveness of the proposal is validated through experimental results based on a three-phase multilevel prototype.

A new low cost cascaded transformer multilevel inverter topology using minimum number of components with modified selective harmonic elimination modulation

In this paper, a novel cascaded transformer multilevel inverter is proposed. The number of the switching devices is reduced in the proposed topology. This topology comprises of a DC source, several single phase low-frequency transformers, two main power switches and some bidirectional switching devices. In this topology, only one bidirectional switch is employed for each transformer. However, in conventional cascaded transformer multilevel inverter, four switching devices are required for each transformer. Therefore, more output voltage levels can be obtained using fewer switching components. Reduction in the number of switching devices which also means reduction in the number of gate drivers results in smaller size and low implementation cost. Switching power losses are also reduced in this topology. Selective harmonic elimination (SHE) technique is applied to the proposed inverter to obtain a high quality output voltage. Simulation and experimental results are also provided to verify the feasibility of the proposed converter.

IMPLEMENTATION OF MULTI TRANSFORMER CELL INVERTER WITH REDUCED SWITCHES IN LAST CELL

This paper proposes an isolated multi transformer cell inverter employing several transformer cells. Some of the cells contain two unidirectional switches that generate two voltage levels and only last cell has five switches that provide five voltage levels. The proposed inverter configuration reduces a number of switches compared with both traditional cascaded transformer multilevel inverter and other multi transformer inverters including six switches in last cell. Also, a prototype has been implemented using DSP-based processor provides a high number of output levels in symmetric and asymmetric states. The operation and performance of the suggested inverter has been proved by simulation result and experimental results.

Single-source cascaded transformers multilevel inverter with reduced number of switches

This study presents a novel topology for multilevel inverters so called cascaded transformer reduced switches inverter (CTRSI). This topology consists of one DC source and several single-phase transformers. Each single-phase transformers generates three levels with two semiconductor switches and only two switches for all transformers alter the direction of single DC source. Whereas each single-phase transformers in conventional cascaded transformer multilevel inverter includes four switches. Hence, CTRSI has the advantage of a reduced number of components compared with conventional cascaded transformer multilevel inverter. Simulation results carried out by MATLAB/SIMULINK and a low-power experimental setup was planned to test the converter in practice. The results show that the proposed inverter topology is able to reach high-quality output voltages. Using switches with higher rating current than conventional topology is main disadvantage of CTRSI.

Reduction of Components in Cascaded Transformer Multilevel Inverter Using Two DC Sources

In this paper a novel cascaded transformer multilevel inverter is proposed. Each basic unit of the inverter includes two DC sources, single phase transformers and semiconductor switches. This inverter, which operates as symmetric and asymmetric, can output more number of voltage levels in the same number of the switching devices. Besides, the number of gate driving circuits is reduced, which leads to circuit size reduction and lower power consumption in the driving circuits. Moreover, several methods to determination of transformers turn ratio in proposed inverter are presented. Theoretical analysis, simulation results using MATLAB/SIMULINK and experimental results are provided to verify the operation of the suggested inverter.

Control of cascaded transformer multilevel inverter based DSTATCOM

In this paper, the design of a distribution static compensator (DSTATCOM) based on cascaded transformer multilevel inverter is proposed. The topology requires controlling only a common dc storage capacitor. Two-level ramp-comparison current control method is extended for the multilevel inverter using phase-shifted multi-carrier PWM. The method provides equal switching stress and power handling for all the cascaded units. The net switching frequency increases while the ripple magnitude reduces using multilevel topology. These cause the feedforward gain to increase leading to a higher bandwidth of the control loop. An expression of the feedforward gain is derived for fixed switching frequency modulation of the inverter. It is shown that the use of proportional plus resonant controller with proposed multilevel modulation improves the tracking characteristics at fundamental frequency. A seven-level inverter based DSTATCOM is proposed for the application to the three-phase medium voltage distribution system and the results are shown through the PSCAD/EMTDC simulation. The proposed modulation and control scheme is validated through the experimental results that are obtained using the laboratory model of a single-phase, five-level inverter based DSTATCOM.