This paper presents a new symmetrical single-phase nine-level dc–ac converter for the applications of distributed generation systems. The proposed multilevel inverter (MLI) utilizes four independent dc sources to generate the nine output voltage levels considering a reduced number of switching devices. The proposed inverter consists of main and auxiliary circuits. The main circuit is a single H-bridge circuit, which is responsible for output voltage polarity. The auxiliary circuit consists of a special combination of switching devices, which are used to synthesize the multilevel output voltage. The merits of the proposed MLI are: increased output voltage levels at reduced number of switching devices, low switching loss, low total harmonic distortion, low dv/dt stress on the switches, and hence, low ratings of the switching devices, and low cost. The effectiveness of the proposed MLI and its pulsewidth modulation switching pattern has been verified experimentally by using a laboratory prototype controlled by DSPACE-1103.

Advanced Single-Phase Nine-Level Converter for the Integration of Multiterminal DC Supplies

Proceedings of the IEEE International Symposium on Industrial Electronics

Isolated single-phase single-stage DC-AC cascaded transformer-based multilevel inverter for stand-alone and grid-tied applications

Multilevel inverters (MLIs) have proven superior performance in several applications, especially in photovoltaic (PV) applications. However, power switches in MLIs possess high failure rates due to unequal power losses distributions that shorten lifetime of the whole PV inverter. Therefore, a new pulsewidth modulation (PWM) methodology for loss balance in grid connected PV single-phase five-level inverters is presented in this paper. The proposed loss balance PWM (LBPWM) method is based on swapping the utilization of power switches through half or quarter of the fundamental line period based on the redundancies between the switching states in MLIs. In addition, the proposed LBPWM method achieves natural balance among voltages over the dc-link capacitors. The effectiveness and feasibility of the proposed LBPWM method are verified using the simulation environment and experimental prototype. Different operating conditions and points of PV inverters are investigated in addition to reliability evaluation of the PV inverter are provided. Moreover, the superior performance criterion of the proposed LBPWM methods are verified through comprehensive comparisons with the most prominent previously developed PWM methods in the literature. The generalization and implementation steps of the proposed LBPWM method are also provided.

Modulation Method for Improving Reliability of Multilevel T-Type Inverter in PV Systems

This paper addresses theoretical calculation of a single-phase multilevel pulsewidth modulation (PWM) inverter current total harmonic distortion (THD). Analytical approach introduced in late 1980s for a two-level inverter is generalized for an arbitrary level count for a single-phase inverter. Although the obtained closed-form piecewise analytical solutions assume (infinitely) large ratio of switching and fundamental frequencies and pure inductive load, they are practically very accurate for the ratios of (apparent) switching and fundamental frequencies larger than 25–30 and inductance-dominated loads. Along with strict mathematical solutions, simple accurate Bessel function approximation and hyperbolic average trend one are suggested. The formulas clearly reveal a single-phase PWM inverter current THD dependence on modulation index for an arbitrary voltage level count and are easily modified to cover grid-connected cases.

Simple Time Averaging Current Quality Evaluation of a Single-Phase Multilevel PWM Inverter

This paper presents a single-phase five-level inverter controlled by two novel pulse width modulation (PWM) switching techniques. The proposed PWM techniques are designed based on minimum switching power loss and minimum total harmonic distortion (THD). In a single-phase five-level inverter employing six switches, the first proposed PWM technique requires four switches to operate at switching frequency and two other switches to operate at line frequency. The second proposed PWM technique requires only two switches to operate at switching frequency and the rest of the switches to operate at line frequency. Compared with conventional PWM techniques for single-phase five-level inverters, the proposed PWM techniques offer high efficiency and low harmonic components in the output voltage. The validity of the proposed PWM switching techniques in controlling single-phase five-level inverters to regulate load voltage is verified experimentally using a 100 V, 500 W laboratory prototype controlled by dspace 1103.

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PWM Control Techniques for Single-Phase Multilevel Inverter Based Controlled DC Cells

This paper presents a single-phase five level Pulse Width Modulation (PWM) inverter. The proposed inverter has the advantage of using less number of components. Two carrier signals identical to each other with an offset equivalent to the amplitude of the triangular carrier signal are used to generate PWM signals for the switches. Some switches operate at fundamental frequency and others operate at switching frequency. Operational principles with switching functions are analyzed. Simulation and experimental results have been done to demonstrate the validity of the proposed inverter. Switches signals are generated using FPGA XC3S400. The proposed inverter has been compared with the conventional single-phase three-level PWM inverter under the conditions of identical dc voltage supply and switching frequency. In addition, it is compared with the well-known five-level PWM inverter found in the literature to highlight the advantage of the proposed inverter.

Single-phase five-level inverter with less number of power elements

Recently, great attention has been addressed for multilevel inverters, as they exhibit low total harmonic distortion (THD) in the output voltage and low electromagnetic interference (EMI). This paper proposes a single-phase five-level pulse width modulation (PWM) inverter for grid connection. The proposed PWM technique has some switches operated at fundamental line frequency and the others operate at inverter switching frequency. The proposed inverter has advantages of less number of components and low THD compared with the conventional multilevel inverter. The inverter operational principles and the switching functions are analyzed in this paper. Moreover, a proportional integral (PI) current control algorithm is designed and implemented in DSPACE DS1103 to keep the current injected into the grid sinusoidal and in-phase with the grid voltage for unity power factor. Simulation and experimental results prove the powerful merits of the proposed multi-level inverter and the capabilities of the proposed PWM technique.

Grid-connected single-phase multi-level inverter

Recently, the emergence of single phase multilevel inverter has been increased due to its advantages over traditional one. This paper proposes a single-phase five level pulse width modulation (PWM) inverter for grid connection employing PI controller to perform unity power factor. Two triangular carrier signals identical to each other with an offset equivalent to the amplitude of the reference signal were used to generate PWM signals for the switches. The proposed inverter has the advantage of less number of components. Operational principles with switching functions are analyzed. A digital proportional integral current control algorithm is implemented in FPGA XC3S400 to control the injected current into the grid to be almost sinusoidal. The inverter offers much less total harmonic distortion and can operate at near-unity power factor. Some switches operate at fundamental frequency and others operate at switching frequency. The proposed inverter has been compared with the conventional single-phase five-level PWM inverter. The effectiveness of the proposed inverter and its control technique has been verified theoretically, using PSIM simulation program, and experimentally, using laboratory prototype system.

Single-phase five-level inverter with less number of power elements for grid connection

http://ieeexplore.ieee.org/iel7/6661669/6661670/06663350.pdf

Maha G. Elsheikh

Papers

PWM Control Techniques for Single-Phase Multilevel Inverter Based Controlled DC Cells

Single-phase five-level inverter with less number of power elements

Grid-connected single-phase multi-level inverter

Single-phase five-level inverter with less number of power elements for grid connection

Low-Cost Single-Phase Multi-Level Inverter for Grid-Tie PV System Applications