Single-stage Dc-ac Power Converters Research Articles

A transformerless three‐level three‐phase boost PWM inverter for PV applications

Multilevel converters have seen rising demands in the past decades, due to their increased power ratings, enhanced power quality, low switching losses and reduced electromagnetic interference. Prominent among them are the three-level (3L) neutral point clamped and the flying capacitor inverter topologies along with their derivatives. Nevertheless, the main drawback of these topologies is the requirement of a front-end boost DC–DC converter to compensate the high dc-link voltage demand, which is usually twice the grid peak voltage. This multi-stage power conversion further pulls down the overall system efficiency. A single-stage dc–ac power converter with boost capability offer an interesting alternative compared to the two stage approach. Considering this aspect, a novel three-level three-phase boost type inverter is introduced in this paper for general-purpose applications (prominently grid-connected renewable energy). The proposed inverter would reduce the DC-link voltage requirement to half using the same or even less number of active and passive components, compared to the conventional three-level neutral point clamped and flying capacitor family. The principle of operation and theoretical analysis are discussed in detail. The design methodology along with simulation and experimental waveforms for a 5 kVA inverter are presented to prove the concept of the proposed inverter topology for practical applications.

Controller Design and Implementation of Solar Panel Companion Inverters

A solar panel companion inverter (SPCI) is a single-stage dc-ac power converter, installed with each solar panel. Each SPCI synthesizes an ac quasi-square wave voltage with variable pulsewidth. The width of ac output voltage of each SPCI is proportional to available power on the solar panel. Output voltages of SPCIs are aggregated across multiple solar panels connected in series, and a sinusoidal ac voltage is synthesized. In this article, dynamic analysis and closed-loop current controller design of SPCI is presented. Simulation results demonstrating the dynamic response of the closed-loop SPCI are included. The closed-loop current control scheme is implemented on a hardware prototype to demonstrate the grid-tied operation of SPCI, and experimental results are presented. A maximum power point tracking (MPPT) algorithm is implemented for sorted stair-case modulation (SSCM) in MATLAB Simulink. Experimental results demonstrating MPPT operation are presented.

Novel Active-Neutral-Point-Clamped Inverters With Improved Voltage-Boosting Capability

Conventional active-neutral-point-clamped (ANPC) inverters exhibit low voltage gain that inherently leads to a high dc-link voltage requirement. An improved ANPC inverter that is capable of generating five voltage levels has recently reduced the dc-link voltage twofold to achieve unity gain. This led to the development of a single-stage dc–ac power converter with no frontend boost dc–dc converter. This article proposes novel ANPC inverters capable of unity or boosted voltage gain while generating higher voltage levels. The first topology can provide a voltage gain of 1.5 and extends the number of levels to seven by incorporating only one additional switch. The topology can also be extended by adding three switches and one floating capacitor to generate nine levels with unity voltage gain, or 11 levels with a voltage gain of 2.5. The proposed ANPC inverters and their operations are comprehensively discussed. Experimental results are provided to validate the feasibility of the proposed ANPC inverters.

Three-Phase Three-Level Flying Capacitors Split-Source Inverters: Analysis and Modulation

Single-stage dc–ac power converters with boost capabilities offer an interesting alternative compared to two-stage architecture. One of the recently proposed single-stage dc–ac power converters is the split-source inverter (SSI). This paper extends the SSI topology from the two-level operation to the three-level one using the flying capacitors (FCs) configuration. Among the diode-clamped SSI (DC-SSI) and FC-SSI, the second one is proposed in order to avoid the need of two isolated dc sources. This paper shows that the FC-SSI provides additional merits compared to the two-level SSI in terms of input inductance requirements using the same switching frequency, voltage stresses across the active switches, and total harmonic distortion of the output voltage. Such results are obtained by discussing the analysis and the modulation of this topology, considering some simulation results, and comparing it to some other existing topologies to show its properties and limitations. Finally, a reduced-scale 1.5-kVA three-level FC-SSI is implemented experimentally to validate its functionality and verify the proposed analysis and modulation properties.