Olive Ray

Synchronous-Reference-Frame-Based Control of Switched Boost Inverter for Standalone DC Nanogrid Applications

Switched boost inverter (SBI) is a single-stage power converter derived from Inverse Watkins Johnson topology. Unlike the traditional buck-type voltage source inverter (VSI), the SBI can produce an ac output voltage that is either greater or less than the available dc input voltage. Also, the SBI exhibits better electromagnetic interference noise immunity when compared to the VSI, which enables compact design of the power converter. Another advantage of SBI is that it can supply both dc and ac loads simultaneously from a single dc input. These features make the SBI suitable for dc nanogrid applications. In this paper, the SBI is proposed as a power electronic interface in dc nanogrid. The structure and advantages of the proposed SBI-based nanogrid are discussed in detail. This paper also presents a dq synchronous-reference-frame-based controller for SBI, which regulates both dc and ac bus voltages of the nanogrid to their respective reference values under steady state as well as under dynamic load variation in the nanogrid. The control system of SBI has been experimentally validated using a 0.5-kW laboratory prototype of the SBI supplying both dc and ac loads simultaneously, and the relevant experimental results are given in this paper. The low cross regulation and the dynamic performance of the control system have also been verified experimentally for a 20% step change in either dc or ac load of SBI. These experimental results confirm the suitability of the SBI and its closed-loop control strategy for dc nanogrid applications.

Boost-Derived Hybrid Converter With Simultaneous DC and AC Outputs

This paper proposes a family of hybrid converter topologies which can supply simultaneous dc and ac loads from a single dc input. These topologies are realized by replacing the controlled switch of single-switch boost converters with a voltage-source-inverter bridge network. The resulting hybrid converters require lesser number of switches to provide dc and ac outputs with an increased reliability, resulting from its inherent shoot-through protection in the inverter stage. Such multioutput converters with better power processing density and reliability can be well suited for systems with simultaneous dc and ac loads, e.g., nanogrids in residential applications. The proposed converter, studied in this paper, is called boost-derived hybrid converter (BDHC) as it is obtained from the conventional boost topology. The steady-state behavior of the BDHC has been studied in this paper, and it is compared with conventional designs. A suitable pulse width modulation (PWM) control strategy, based upon unipolar sine-PWM, is described. A DSP-based feedback controller is designed to regulate the dc as well as ac outputs. A 600-W laboratory prototype is used to validate the operation of the converter. The proposed converter is able to supply dc and ac loads at 100 V and 110 V (rms), respectively, from a 48-V dc input. The performance of the converter is demonstrated with inductive and nonlinear loads. The converter exhibits superior cross-regulation properties to dynamic load-change events. The proposed concept has been extended to quadratic boost converters to achieve higher gains.

Integrated Dual-Output Converter

This paper presents a family of single-input-multiple-output (SIMO) dc-dc converter topologies, which can provide one step-up and multiple step-down outputs. These topologies are synthesized by replacing the control switch of a boost converter topology with series-connected switches and using the additional switch nodes to generate step-down dc outputs. Compared with separate converters, these topologies utilize a lower number of switches and are more reliable due to their inherent shoot-through protection. Analysis shows that the topologies exhibit similar dynamic behavior as individual buck and boost converters. Hence, the control system methodology is the same as that of separate converters, with each output being precisely regulated. The behavior of these converters has been illustrated in this paper using the integrated dual-output converter (IDOC), which has a step-up and a step-down output. The steady-state characteristics and dynamic behavior of the converter have been studied. An analog closed-loop control system for the converter has been described for regulation of both the outputs. The operating principles have been experimentally validated using a 120-W prototype. Results show that the proposed converter has very good cross-regulation to step load change as well as dynamic reference change in either output. The measured efficiencies of the IDOC prototype are around 90%.

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.

Advances in nanogrid technology and its integration into rural electrification in India

Nanogrids are small residential power systems with renewable sources, storage, and domestic loads. It may or may not have connectivity to utility grid. This paper discusses the role of advanced converter technology for Nanogrids in solving acute power shortage problem in Rural India. The paper is divided into two sections. In the first section, the advances in Nanogrid converter technology are discussed. The implementations and advantages of multi-output converters are delineated. In the second section, some proposals are presented to incorporate these new technologies for easy adaption in rural electrification. A prototype is built using off-the-shelf components and commercial loads to prove the usability of the proposed concepts.

DSP based PWM control of Switched Boost Inverter for DC nanogrid applications

Switched Boost Inverter (SBI) is a buck-boost type dc to ac converter derived from Inverse Watkins Johnson (IWJ) Topology. This converter can supply both DC and AC loads simultaneously which makes it suitable for DC nanogrid applications. In order to invoke the boost operation, the SBI utilizes shoot-through state of the inverter bridge. So, the traditional Pulse Width Modulation (PWM) techniques of Voltage Source Inverter (VSI) have to be modified to incorporate the shoot-through interval in each switching cycle, so that they are suitable for SBI. This paper presents a PWM control strategy developed for SBI, and describes its implementation in digital domain using the enhanced PWM (ePWM) modules of TMS320F28335 Digital Signal Processor (DSP). This paper also presents a soft start method of SBI to limit the inrush current at the start-up. The PWM signals generated by the DSP are used to control a laboratory prototype of SBI supplying both DC and AC loads. The steady state and start-up waveforms of the converter are presented for verification of the DSP based PWM control technique and the soft-start method described in the paper. The experimental results show good correlation with the theoretical analysis given in the paper.

Implementation and control of a bidirectional high-gain transformer-less standalone inverter

This paper describes a bidirectional inverter topology for standalone applications. The topology, consisting of a Quadratic Boost Converter based Voltage Source Inverter (VSI), can achieve high conversion ratio both in inverter as well as rectifier operations without the use of a transformer. In addition, the same architecture can also be used to realize DC-DC conversion (both Step-Up and Step-Down). This improves the adaptability of the topology in renewable system realization, especially in rural areas, and makes it suitable to handle variable input sources. The bidirectional power transfer capability with high conversion ratio is demonstrated using a lab prototype. The controller design for the topology operating as a standalone inverter is described in a step-by-step manner and this has been implemented using TMS320F28335 DSP. The output voltage regulation capability, when the high-gain inverter is subjected to load-step changes as well as variable input, has been validated using experimental results.

A multi-port DC-DC converter topology with simultaneous buck and boost outputs

Multi-port DC-DC converter topologies can be used to generate multiple DC outputs from a single DC input source — the voltage gains can be step-up and/or step-down type. Compared to dedicated converters, these integrated topologies have higher efficiencies, lesser Bill-of-Material, as well as lesser coordination communication requirements. This paper proposes a multi-port DC-DC converter topology which generates two outputs — step-up as well as step-down, from a single DC input. The converter architecture is realized by replacing the controlled switch of a boost converter with a half bridge network and a low pass filter. Compared to traditional buck converters, the proposed converter has higher reliability, due to its inherent shoot-through protection and has a wider range of step-down outputs. In contrast to two separate buck and boost converters, this proposed topology performs the same function with lesser number of switches. Operating modes and steady state behavior of the proposed converter has been studied in this paper. A suitable control scheme to control both outputs has been described. The behavior of the proposed converter has been verified using a 150 W laboratory prototype, which produces a step-up voltage of 18 V and a step-down voltage of 6 V from a single 12 V input.

A multi-port converter topology with simultaneous isolated and non-isolated outputs

DC based Nanogrids are being increasingly implemented in modern residential applications for realizing smarter and greener energy efficient systems. The total power requirement for these applications can be realized by small localized generation systems (typically, renewable sources), which serve a wide variety of consumer loads. Some of the loads in these applications may be critical in nature and may require being galvanically isolated to the input supply. This paper proposes a multi-port power converter architecture which can provide two outputs - isolated as well as non-isolated from a single DC input. Thus, both isolated and non-isolated loads can be served by a single converter topology in a Nanogrid. The salient features for the converter include its inherent shoot-through protection and the ability to regulate both the outputs independently using integrated control architecture. The characteristics of the converter have been studied in this paper and a PWM scheme developed for the purpose of controlling both the outputs. The proposed operation has been verified using experimental results obtained from a laboratory prototype.

Integrated hybrid output converter as power router for renewable-based nanogrids

Renewable energy sources are being increasingly integrated into power distribution systems to reduce the burden of conventional utility-based system and simultaneously reducing the carbon footprint. The uncertainties associated with these renewable sources coupled with load variation dictate the use of power electronic converters for the purpose of power conditioning and for maintaining system stability. These power conditioners play the role of a Power Router in order to effectively channelize the extracted power into the existing distribution system. The paper investigates the use of Integrated Hybrid Converter Technology as Power Routers in a dc nano grid scenario. The different operating modes of the hybrid converter with their associated power dynamics within the distribution system have been studied. Experimental results have been shown to validate the concept.