Active utilization of a full DC-Link voltage in multilevel converter

© 2018 IEEE. Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy conversion. Multilevel inverter reduces the inductors and filters size, whilst improving the output power quality. However, the main drawback of the multi-level inverter topologies is that they utilizes only ≤ 50% of the input dc-bus voltage, i.e. they require two times the peak of ac output voltage. For example, the nominal input voltage of the NPC, ANPC and Flying Capacitor is 800 V dc . This high dc-link voltage not only requires higher voltage components (both active and passive) but also prompts to use an additional front-end boost dc-dc converter. Considering these aspects, this paper presents a novel technique to extend the input dc-bus voltage utilization in any conventional multilevel inverter from ≤ 50% to ≤ 100%. The novel technique utilizes an additional T-type module (consist of four active switches), which is inserted just before the two dc-link capacitor forming a new grounding point. The novel method not only reduces the input voltage requirement and voltage stress, but also increases the output voltage levels of the inverter. In general, this technique can be implemented to any multilevel inverter. An example of implementation of 5L inverter from the conventional 3-Level T-type inverter is discussed and validated. Measurement results shows that the new Dual T-type inverter has a flat efficiency « 99 % over a wide range of load

Novel High Efficiency H-Bridge Transformerless Inverter for Grid-Connected Single-Phase Photovoltaic Systems

© 2018 IEEE. This paper proposes a new H-bridge type transformerless inverter for grid-connected photovoltaic (PV) application. The proposed H-bridge zero voltage switch controlled rectifier (HB-ZVSCR) inverter uses additional switches and diodes at the AC side with voltage clamping feature to the DC midpoint. Main characteristics of the proposed inverter are the high conversion efficiency and low leakage current, which make it a suitable candidate for grid-connected PV applications. The analysis and operating principles of the proposed inverter are discussed in details. This theoretical findings has been simulated using PLECS software to verify the common mode voltage (CMV) and leakage current behaviors and the results are compared with similar existing midpoint voltage clamping inverter topologies (i.e. HB-ZVR and HB-ZVR-D). Furthermore, power loss and efficiency of the proposed inverter have been evaluated and compared with existing topologies

AC small signal modeling of PWM Y-source converter by circuit averaging and averaged switch modeling technique

© 2016 IEEE and EPE Association. Magnetically coupled Y-source impedance network is a newly proposed structure with versatile features intended for various power converter applications e.g. in the renewable energy technologies. The voltage gain of the Y-source impedance network rises exponentially as a function of turns ratio, which is inherited from a special coupled inductor with three windings. Due to the importance of modeling in the converter design procedure, this paper is dedicated to dc and ac small signal modeling of the PWM Y-source converter. The derived transfer functions are presented in detail and have been verified through simulation and experimental results

Switched-capacitor integrated single-phase (2n+1)-levels boost inverter for grid-tied photovoltaic (pv) applications

© 2019 IEEE. This paper presents a switched-capacitor integrated (2N+1)-level (N≥2) boost inverter for single-phase photovoltaic (PV) applications. It consists of N modular switching cells, where each cell consists of two switched capacitors and three active switching elements. A boost converter at the front side of the switching cells helps to maintain the capacitor voltage balance during different operation modes. With this arrangement, the inverter is capable to generate 2N+1 output voltage levels, and able to accommodate a wide range of input voltage. Detailed analysis followed by simulation and experimental results of a 5-level inverter as an example is presented to verify the proposed concept. Further, comparison with other multilevel inverter topologies is presented to show the merit of the proposed concept

A novel seven-level active neutral-point-clamped converter with reduced active switching devices and DC-link voltage

© 1986-2012 IEEE. This paper presents a novel seven-level inverter topology for medium-voltage high-power applications. It consists of eight active switches and two inner flying capacitor (FC) units forming a similar structure as in a conventional active neutral-point-clamped (ANPC) inverter. This unique arrangement reduces the number of active and passive components. A simple modulation technique reduces cost and complexity in the control system design without compromising reactive power capability. In addition, compared to major conventional seven-level inverter topologies, such as the neutral point clamped, FC, cascaded H-bridge, and ANPC topologies, the new topology reduces the dc-link voltage requirement by 50%. This recued dc-link voltage makes the new topology appealing for various industrial applications. Experimental results from a 2.2-kVA prototype are presented to support the theoretical analysis presented in this paper. The prototype demonstrates a conversion efficiency of around 97.2% ± 1% for a wide load range

H-Bridge Zero-Voltage Switch Controlled Rectifier (HB-ZVSCR) Transformerless Mid-Point-Clamped Inverter for Photovoltaic Applications

A single-phase transformerless mid-point clamped H-bridge zero-voltage switch-controlled rectifier inverter topology is proposed in this paper for photovoltaic (PV) systems to address the issue of common mode (CM) voltage and leakage currents. Apart from the full H-bridge inverter, the proposed voltage clamping circuit consists of two switches and a full-bridge diode which clamps the AC terminal to the DC midpoint (consisting of two DC-link capacitors) during the freewheeling period. As a result, the common mode voltage is held constant which makes it suitable for the grid-connected PV system. The operating principle and CM effect of the proposed topology are analysed and compared with the conventional topologies. This is followed by the thermal analysis and loss calculation, which shows that the proposed circuit is more efficient over the conventional topologies. Validation is carried out using MATLAB-Simulink using the PLECS toolbox followed by a scale down prototype of 1.5 kW. It is shown that the proposed inverter has the 98±1% efficiency over a wide range of loads with a peak efficiency of 98.96%, and the total harmonic distortion of the output current relatively low (≤1.8 %). The leakage current (icm) is measured for different values of parasitic capacitance that reaches a maximum of 16.65 mA for 330 nF capacitor under consideration which is well below the limit set by different safety standard

Multi-variable thermal modeling of power devices considering mutual coupling

© 2019 by the authors. In relation to power converter design, power density is increasing while the form factor is decreasing. This trend generally reduces the rate of the cooling process, which increases the mutual thermal coupling among the surrounding power components. Most of the traditional models usually ignore the mutual effects or just focus on the conduction coupling. To deal with these factors, the thermal modeling for a boost converter system has been built to compare the junction temperatures (Tj) and the increments under different working conditions in order to consider the conduction coupling. A multi-variable thermal resistances model is proposed in this paper to incorporate the convection thermal coupling into the mutual thermal effects. The coupling resistances, MOSFET to the diode (Rcp-DM ⇀), and the diode to MOSFET (Rcp-DM ⇀) have been calculated and the relationships between coupling resistances and their impact factors (separation distances and working currents) have been discussed. New case temperatures (Tc) obtained by calculation and additional measurements at other separation distances serve to verify the efficacy of the proposed model. This model enhances the current thermal models and provides an effective method to calculate the thermal coupling resistances which can be used to estimate the Tj. As the coupling resistances are distance dependent, the model also helps to optimize and fine-tune the placements of components in high-power density converters

A trans-inverse coupled-inductor semi-SEPIC DC/DC converter with full control range

© 1986-2012 IEEE. This letter proposes a single switch magnetically coupled dc-dc converter with a high voltage gain. The unique features of the converter are summarized as follows: 1) voltage gain of the converters is raised by lowering its magnetic turn ratio; 2) wide control range (0< D< 1); 3) continuous current from the source that makes it a suitable candidate for renewable energy applications; and 4) there is no dc current saturation in the core due to the presence of capacitor in the primary winding of the inductor. The feasibility of the proposed converter is studied in details supported by circuit analysis and simulation results. Furthermore, the proposed converter is analyzed and compared with other converters with similar features. Finally the superior performance of the circuit is validated experimentally