Soumya Shubhra Nag

Current-Fed Switched Inverter

High-boost dc-ac inverters are used in solar photovoltaic (PV), fuel cell, wind energy, and uninterruptible power supply systems. High step-up and step-down capabilities and shoot-through immunity are some of the desired properties of an inverter for a reliable, versatile, and low-distortion ac inversion. The recently developed Z-source inverter (ZSI) possesses these qualities. However, the realization of ZSI comes at a cost of higher passive component count as it needs two sets of passive filters. A switched boost inverter (SBI) has similar properties as ZSI, and it has one L-C pair less compared to ZSI, but its gain is less than ZSI. This paper proposes the current-fed switched inverter (CFSI) which combines the high-gain property of ZSI and low passive component count of SBI. The proposed inverter uses only one L-C filter and three switches apart from the inverter structure. The inverter topology is based on current-fed dc/dc topology. Steady-state analysis of the inverter is presented to establish the relation between the dc input and the ac output. A pulse width modulation (PWM) control strategy is devised for the proposed inverter. An experimental prototype is built to validate the proposed inverter circuit in both buck and boost modes of operation. A 353-V dc-link and a 127 V (rms) ac are obtained from a 35.3-V dc input to demonstrate the boost mode of operation. A 200-V dc-link and a 10.5-V (rms) ac are obtained from a 37.8-V dc input to verify the buck mode of operation of CFSI.

Current-Fed Switched Inverter based hybrid topology for DC Nanogrid application

High boost DC to AC inverters are used in renewable energy systems like solar PV, fuel cell, wind farm etc and UPS systems to mention a few. High voltage boost, wide output ranges of operation, shoot-through immunity are some of the desired properties of an inverter for a reliable, versatile and low distortion AC inversion. This paper proposes a single-stage, high boost inverter with buck-boost capability which has several distinct advantages over conventional voltage source inverters (VSI) like better EMI noise immunity, wide input and output voltage range of operation, etc. The proposed inverter is named as Current-Fed Switched Inverter (CFSI). A hybrid converter structure of CFSI has been developed which supplies both AC and DC loads, simultaneously, from a single DC supply which makes it suitable for DC Nanogrid application. This paper proposes the operation and control of a CFSI based hybrid converter which regulates the AC and DC bus voltages at their reference values in steady-state or dynamic load change event. The development of the proposed converter from basic current-fed DC/DC topology is discussed. Steady-state analysis of the converter is outlined to establish the relation between DC input and AC output. Small-signal analysis of the converter is done to design the closed loop controller for the converter. An experimental prototype is built to validate the proposed converter with its DSP based closed loop control. The closed loop controller is verified through its low cross regulation and dynamic performance for a 20% step change in either DC or AC load.

A Passive Filter Building Block for Input or Output Current Ripple Cancellation in a Power Converter

This paper analyzes a coupled inductor based LL-LC network as a building block to achieve input or output current ripple cancellation in power converters. The proposed current ripple cancellation technique works on the principle of inductance matching. It also provides reduced current stress on the switching devices of the converter compared with the other current ripple cancellation networks discussed in the literature. The current ripple cancellation technique is verified in achieving input and output current ripple minimization in different converters. The effect of inductance mismatch, inductor and capacitor tolerances, and circuit parasitic is also studied. Some of the published research works are demonstrated to be a special case of the proposed idea. The effectiveness of the proposed method is validated by demonstrating the zero-ripple input current using a 31 V dc to 60 V dc, 240 W boost converter prototype and a 31 V dc to 115 V (rms) ac, 320 W current-fed-switched inverter prototype, and the zero-ripple output current using a 62 V to 42 V dc, 450 W buck converter prototype.

A Coupled Inductor Based High Boost Inverter with Sub-unity Turns-Ratio Range

Voltage source inverter cannot provide an output voltage higher than its input and needs a dead-time scheme for its switches to prevent dc-link short circuit due to spurious turn-on of switches by electromagnetic interference (EMI). Impedance source inverters have eliminated these disadvantages by providing boost functionality with improved EMI immunity. Coupled inductor-based impedance source inverters provided increased gain at the expense of increased coupled inductor turns-ratio. In this paper, a coupled inductor based high gain inverter is proposed, which achieves higher gain by increasing the coupled inductor turns-ratio (n = n2/n1) within a very narrow turns-ratio range of 0 ≤ n <; 1, which is a major improvement over the other coupled inductor based high boost impedance source inverters. The proposed inverter, named Improved Trans-Current-Fed Switched Inverter, is described along with its equivalent operating states and relation between its input and output variables are derived. The steady-state inverter waveforms are shown using PSpice simulations. The operation of the inverter is validated by the experimental results, which show strong correlation with the theoretical analysis. A 110-V RMS ac output is obtained from 26-V dc input using a coupled inductor with turns-ratio of 0.33 to demonstrate its high-boost operation.

Current-Fed DC/DC topology based inverter

New-age power generation systems based on renewable energy systems (RES) mainly constitute of wind generators, solar PV, fuel cells, etc. Energy harvesting from solar PV or fuel cell calls for high step-up inversion owing to its low-voltage input. Conventional voltage source inverter (VSI) can only produce an AC output smaller than its input DC voltage under normal operation. VSI also requires for dead-time compensation circuits as shoot-through of any inverter leg is detrimental for its operation. Recently developed ZSI and its derivatives overcome these problems by allowing shoot-through and providing output AC voltage with buck-boost capability. This paper proposes a Current-Fed DC/DC Topology (CFT) based inverter which shows similar gain characteristic and advantages as the ZSI. The proposed inverter requires only one LC-pair which is one less than the impedance network of ZSI. The proposed inverter is derived from CFT. Steady-state analysis and implementation of the proposed inverter are described. The PWM control strategy of the inverter is explained. An experimental prototype is built to validate the proposed inverter circuit. A 127 V (rms) AC-output is obtained from 353 V DC-link with 35.3 V DC-input and a 5.18 V (rms) AC-output is obtained from 57.6 V DC-link voltage with 28.8 V DC-input to verify boost and buck mode of operation, respectively.

Coupled inductor based Current-Fed Switched Inverter for low voltage renewable interface

This paper presents a novel coupled inductor based high boost inverter topology which can be utilized in low voltage renewable systems where high voltage step-up is needed to interface with 110 V/220 V AC systems. The proposed inverter possesses high boost ability with superior EMI immunity compared to a traditional voltage source inverter (VSI). Unlike the traditional VSI, the proposed inverter does not need dead-time circuit for its switching signals as it utilizes shoot-through state of the inverter in its single-stage configuration. Insertion of shoot-through state also helps it to achieve high boost operation essential for renewable energy applications. The proposed inverter is derived from Current-Fed Switched Inverter topology. Apart from topology derivation, this paper describes the steady-state analysis of the inverter and establishes the relation between input, DC-link, and AC output. An experimental prototype is built to validate the proposed inverter circuit. A 220 V (rms) AC is obtained from 52 V DC input to demonstrate its boost mode of operation.

Improved trans-current-fed switched inverter

Very high voltage boost is an essential requirement for connecting small voltage renewable sources to the standalone residential system or to the grid. Current-Fed Switched Inverter (CFSI) can provide a very high boost utilizing the shoot through of its inverter legs. Apart from high boost, CFSI also offers continuous input current and low passive component count which makes it suitable for renewable applications. Coupled inductor based topologies found in the literature provides increased gain at the expense of increased coupled inductor turns ratio. This paper presents a novel coupled inductor based CFSI topology in which higher gain is achieved by lowering the coupled inductor turns ratio (n), unlike other coupled/tapped inductor topologies. The proposed inverter, named Improved Trans-Current Fed Switched Inverter (Improved Trans-CFSI), offers higher gain with smaller coupled inductor turns ratio, which is a major improvement over the other coupled inductor based high boost inverter topologies where higher turns ratio is required to achieve higher gain. The paper presents the detailed steady-state analysis of the proposed inverter and establishes the relation between their input output parameters. The operation of the inverter is validated by the experimental results which show strong correlation with the theoretical analysis.

Three winding coupled inductor based high boost inverter with increased gain control

Renewable sources like solar PV, fuel cell, etc., needs high boost inversion in order to connect to utility supply due to their low output voltage nature. Apart from high gain, some other desirable features of the inverter are low component count, high efficiency, low footprint, immunity to spurious signals like EMI. In this paper a three winding coupled inductor based inverter topology is presented which can provide a very high voltage boost by utilizing the shoot through of its inverter legs. The proposed inverter uses only one coupled inductor, one capacitor as passive components in its structure which makes it suitable for renewable applications. Generally coupled inductor based topologies provide increased gain at the expense of increased coupled inductor turns ratio beyond unity, but the gain of the proposed inverter can be made higher by increasing the tertiary to primary winding turns ratio from zero to unity. The gain can be also increased by increasing tertiary to secondary winding turns apart from increasing shoot-through duty and modulation index. Thus the proposed inverter provides more variables to control gain. The paper presents the detailed steady-state analysis of the proposed inverter and establishes the relation between their input-output variables. The operation of the inverter is validated by the experimental results.

Improving Grid Power Availability in Rural Telecom Exchanges

India has seen a huge surge in the telecom sector with total rural telecom subscribers doubling from 200.81 million to 404.16 million between 2010 and 2015. Therefore, telecom exchanges are built throughout the country to support this development. With severe electric power shortages in rural India, it poses a challenge to power these exchanges. It is observed that power supply in rural areas is not always available in three phase and can sometimes be available in two or single phase depending on fault in the three-phase system. Currently, used power plants in telecom exchanges are not designed to adapt to these variable input phase conditions. In this paper, a method is proposed to modify the currently used power plants such that they easily adapt to variable input phase conditions. This will lead to the utmost utilization of grid power and save valuable diesel fuel used in back-up diesel generators. The proposed method is designed and verified to have reasonable input power quality as per international standards. A quantitative estimation of diesel savings is also presented to estimate the percentage of diesel savings as a function of power outage.

Synthesis of buck converter based current sources

Ripple free DC or AC current source can be implemented by operating a switching converter in current mode control and setting the switching frequency much higher than the operating frequency. However, due to presence of the output filter across the load, it exhibits deviation from the ideal output impedance characteristics of an ideal current source. In this paper, a DC and an AC current source are presented which provides low ripple output current without sacrificing the high output impedance characteristics of an ideal current source. The DC and AC current sources are realized using a buck converter and a voltage source inverter, respectively with a coupled LL-LC output filter replacing the traditional LC output filter. The low ripple output current is obtained by utilizing the notch behavior of the coupled LL-LC filter. The operating principle of the proposed current source structures are explained in details. The performances of the proposed current sources are validated using simulations and experiments. The proposed DC current source and sinusoidal AC current source shows only 0.4% and 1.33% ripple content at their output current, respectively.