Recently, multilevel inverters (MLIs) have gained lots of interest in industry and academia, as they are changing into a viable technology for numerous applications, such as renewable power conversion system and drives. For these high power and high/medium voltage applications, MLIs are widely used as one of the advanced power converter topologies. To produce high-quality output without the need for a large number of switches, development of reduced switch MLI (RS MLI) topologies has been a major focus of current research. Therefore, this review paper focuses on a number of recently developed MLIs used in various applications. To assist with advanced current research in this field and in the selection of suitable inverter for various applications, significant understanding on these topologies is clearly summarized based on the three categories, i.e., symmetrical, asymmetrical, and modified topologies. This review paper also includes a comparison based on important performance parameters, detailed technical challenges, current focus, and future development trends. By a suitable combination of switches, the MLI produces a staircase output with low harmonic distortion. For a better understanding of the working principle, a single-phase RS MLI topology is experimentally illustrated for different level generation using both fundamental and high switching frequency techniques which will help the readers to gain the utmost knowledge for advance research.

/pdf/recently-developed-reduced-switch-multilevel-inverter-for-4lxrfejht6.pdf

Recently Developed Reduced Switch Multilevel Inverter for Renewable Energy Integration and Drives Application: Topologies, Comprehensive Analysis and Comparative Evaluation

Multilevel inverters (MLIs) have gained increasing interest for advanced energy-conversion systems due to their features of high-quality produced waveforms, modularity, transformerless operation, voltage, and current scalability, and fault-tolerant operation. However, these merits usually come with the cost of a high number of components. Over the past few years, proposing new MLIs with a lower component count has been one of the most active topics in power electronics. The first aim of this article is to update and summarize the recently developed multilevel topologies with a reduced component count, based on their advantages, disadvantages, construction, and specific applications. Within the framework, both single-phase and three-phase topologies with symmetrical and asymmetrical operations are taken into consideration via a detailed comparison in terms of the used component count and type. The second objective is to propose a comparative method with novel factors to take component ratings into account. The effectiveness of the proposed method is verified by a comparative study.

Voltage Source Multilevel Inverters With Reduced Device Count: Topological Review and Novel Comparative Factors

Recently multilevel inverters (MLIs) have received wide attention from industry and academia, as they are changing into a viable technology for diverse applications. To produce high-quality output using less switch count, development of novel reduced switch MLI (RS MLI) topologies has been a focus of current research theme. This paper presents design and control of a switched-diode dual source single switch MLI (SDDS MLI). The generalized SDDS MLI is first designed using an asymmetric basic unit. Proposed SDDS MLI requires less switch count and driver circuit count compared with the few recently developed RS MLI topologies. To improve the voltage quality by eliminating targeted low-order harmonics, a modified version of fish swarm optimization algorithm is examined for computing optimum switching angles required to control the SDDS MLI. Moreover, suitability and superiority of the derived algorithm are established by comparing with traditional selective harmonic elimination techniques. The developed topology is investigated through several MATLAB simulations as well as experimental tests in the laboratory applying the modified control approach.

Reduced Switch Cascaded Multilevel Inverter With New Selective Harmonic Elimination Control for Standalone Renewable Energy System

This article proposed a single-source multilevel inverter (MLI) based on the novel K-type unit (KTU). The 13-level topology with two KTUs and 1.5 voltage gain is first introduced, and its operation modes at different output levels are described in this article. The two capacitors in series connection with each KTU can get self-voltage balance due to their symmetric operation in a cycle, reducing the complexity of control compared with conventional MLIs. The analysis of self-balance and capacitance calculation are given in detail. Afterward, the single-source generalized structure equipped with more KTUs is presented for increasing output levels. The output levels are significantly increased with additional KTUs, and the voltage gain rises as well. Moreover, through the comparative study against other MLI topologies proposed in recent years, the advantages of the proposed KTU topology are indicated in the aspects for reduced components, self-balance, voltage stress, and overall cost. Finally, the 13-level simulation and 1-kVA experimental prototype with fundamental frequency modulation (FFM) are implemented to verify the feasibility and transient performance of the proposed topology.

Novel K-Type Multilevel Inverter With Reduced Components and Self-Balance

Over the last decade, energy demand from the power grid has increased significantly due to the increasing number of users and the emergence of high-power industries. This has led to a significant increase in global emissions with conventional energy generation. Therefore, the penetration of renewable energy resources into the power grid has increased significantly. Photovoltaic systems have become the most popular resources as their protentional is enormous, thus, the worldwide installed PV capacity has increased to more than 635 gigawatts (GW), covering approximately 2% of the global electricity demand. Power electronics are an essential part of photovoltaic generation; the drive for efficient power electronic converters is gaining more and more momentum. Presently, multilevel inverters (MLI) have become more attractive to researchers compared to two-level inverters due to their abilities to provide lower electromagnetic interference, higher efficiency, and larger DC link voltages. This paper reviews multilevel inverters based on their classifications, development, and challenges with practical recommendations in utilizing them in renewable energy systems. Moreover, PV systems with various maximum power point tracking (MPPT) methods have been extensively considered in this paper as well. The importance and the development of a modified multilevel inverter are also highlighted in this review. In general, this paper focuses on utilizing multilevel inverters for PV systems to motivate and guide society to focus on inventing an efficient and economical multilevel inverter that has the combined capabilities of these converters reported in the literature.

https://www.mdpi.com/1996-1073/14/6/1585/pdf

Review of Multilevel Inverters for PV Energy System Applications

In this paper, a new topology of two-stage cascaded switched-diode (CSD) multilevel inverter is proposed for medium-voltage renewable energy integration. First, it aims to reduce the number of switches along with its gate drivers. Thus, the installation space and cost of a multilevel inverter are reduced. The spike removal switch added in the first stage of the inverter provides a flowing path for the reverse load current, and as a result, high voltage spikes occurring at the base of the stepped output voltage based upon conventional CSD multilevel inverter topologies are removed. Moreover, to resolve the problems related to dc source fluctuations of multilevel inverter used for renewable energy integration, the clock phase-shifting (CPS) one-cycle control (OCC) is developed to control the two-stage CSD multilevel inverter. By shifting the clock pulse phase of every cascaded unit, the staircase-like output voltage waveforms are obtained and a strong suppression ability against fluctuations in dc sources is achieved. Simulation and experimental results are discussed to verify the feasibility and performances of the two-stage CSD multilevel inverter controlled by the CPS OCC method.

Novel Cascaded Switched-Diode Multilevel Inverter for Renewable Energy Integration

One-cycle controlled Cuk converters are prone to exhibit oscillation at the input stage as a result of Hopf bifurcation. A controller based on time delay feedback is proposed to eliminate the oscillation and stabilize the converter. The controller introduces two new parameters, which are known as the feedback gain and the delayed time. These two parameters are of great importance in stabilizing the converter. The averaged model of the converter is adopted to select the parameters. A necessary condition for the converter to be stabilized gives an effective range of the two parameters. An experimental Cuk converter was constructed for verification purposes. The waveforms in front of load changes are provided. The results show that the proposed controller eliminated the oscillation in the input stage of the converter. The controller allows widening of the stability domain and decreases switch voltage stress in the input stage of the one-cycle controlled Cuk converter.

Hopf Bifurcation and Its Control in the One-Cycle Controlled Cuk Converter

Power Factor Correction (PFC) converters are widely used in engineering. A classical PFC control circuit employs two complicated feedback control loops and a multiplier, while the One-Cycle-Controlled (OCC) PFC converter has a simple control circuit. In OCC PFC converters, the voltage loop is implemented with a PID control and the multiplier is not needed. Although linear theory is used in designing the OCC PFC converter control circuit, it cannot be used in predicting non-linear phenomena in the converter. In this paper, a non-linear model of the OCC PFC Boost converter is proposed based on the double averaging method. The line frequency instability of the converter is predicted by studying the DC component, the first harmonic component and the second harmonic component of the main circuit and the control circuit. The effect of the input voltage and the output capacitance on the stability of the converter is studied. The correctness of the proposed model is verified with numerical simulations and experimental measurements.

https://www.mdpi.com/2079-9292/7/9/203/pdf

Line Frequency Instability of One-Cycle-Controlled Boost Power Factor Correction Converter

The previously developed control methods based on the conservation of energy in circuits require the accurate estimation of energy losses, which is difficult to measure and calculate for boost converters Consequently, there always exist steady-state errors in the output voltage if neglecting such circuit energy losses To address this issue, an improved energy balance control (IEBC) method is proposed in this paper by integrating a simplified energy balance controller (SEBC) with a PI controller The proposed IEBC can reduce the steady-state output voltage errors without requiring the estimation of circuit energy losses Furthermore, the proposed IEBC can operate in both the continuous current mode (CCM) and the discontinuous current mode (DCM), thus accurate static and fast dynamic performances are achieved over the entire load operation range Moreover, the stability of the IEBC is proved using the Lyapunov stability criterion Compared with that of the SEBC, both simulations and experiments validate the feasibility and robustness of the proposed IEBC method

/pdf/improved-energy-balance-control-for-boost-converters-without-1v27r2fguc.pdf

Improved Energy Balance Control for Boost Converters Without Estimating Circuit Energy Losses

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Papers

Novel Cascaded Switched-Diode Multilevel Inverter for Renewable Energy Integration

Hopf Bifurcation and Its Control in the One-Cycle Controlled Cuk Converter

Line Frequency Instability of One-Cycle-Controlled Boost Power Factor Correction Converter

Novel Cascaded Switched-Diode Multilevel Inverter for Renewable Energy Integration

Improved Energy Balance Control for Boost Converters Without Estimating Circuit Energy Losses