Ravindranath Adda

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.

Inverse Watkins–Johnson Topology-Based Inverter

A Z-source inverter (ZSI) uses an L-C impedance network between the source and the voltage source inverter (VSI). It has the property of stepping down or stepping up the input voltage, as a result, the output can be either higher or lower than the input voltage as per requirement. This topology also possesses robust electromagnetic interference noise immunity, which is achieved by allowing shoot through of the inverter leg switches. This letter proposes an inverter circuit based on the inverse Watkins-Johnson (IWJ) topology that can achieve similar advantages as that of a ZSI. The proposed circuit requires two switches and one pair of an LC filter apart from the VSI. The systematic development of this inverter topology is described starting from the basic IWJ circuit. Steady-state analysis and implementation of the proposed topology are also described. The pulse width modulation control strategy of the inverter is explained. An experimental prototype is used to validate the proposed circuit.

A PWM control strategy for switched boost inverter

Switched Boost Inverter is a single stage dc-ac power converter, whose output voltage can be either greater or less than its input dc voltage. This converter can supply both dc and ac loads, simultaneously, which makes it suitable for microgrid applications. Also, this converter allows shoot-through of the inverter legs without causing any damage to the converter. In this paper, the principle of operation of the Switched Boost Inverter is explained in detail and the expression for its conversion ratio is derived. Also, a Pulse Width Modulation (PWM) control strategy for the Switched Boost Inverter is formulated and implemented using a simple analog circuit. The harmonics spectrum of the inverters output voltage with the proposed PWM technique is plotted and compared with that of a traditional voltage source inverter (VSI). Experimental results are provided to verify proposed converter and its control along with its theoretical analysis.

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.

Switched-boost inverter based on Inverse Watkins-Johnson topology

Z-source inverter (ZSI) uses an L-C impedance network between the source and the voltage source inverter (VSI). It has the property of stepping down or stepping up the input voltage, as a result, the output can be either higher or lower than the input voltage as per requirement. This topology also possesses robust Electromagnetic Interference (EMI) noise immunity, which is achieved by allowing shoot-through of the inverter leg switches. This paper proposes an inverter circuit based on Inverse Watkins-Johnson topology that can achieve similar advantages as that of a ZSI. The proposed circuit requires two switches and one pair of LC filter apart from the VSI. The systematic development of this inverter topology is described starting from the basic Inverse Watkins-Johnson circuit. Steady-state analysis and implementation of the proposed topology are also described. The PWM control strategy of the inverter is explained. An experimental prototype is used to valid the proposed circuit.

A switched-boost topology for renewable power application

This paper proposes a novel switched-boost converter suitable for microgrid application. The proposed converter can provide a DC output, which is greater than the input voltage. Apart from a DC, it can be, simultaneously, used to supply an AC load. In order to supply an AC load it has to be cascaded with a Voltage source inverter (VSI). While operating with a VSI, it avails all the advantages of a Z-source inverter, with half the number of passive components. During AC operation, it prevents the shoot-though current due to mis-gating and provides superior noise immunity. The circuit operation, analysis, PWM control strategy, and experimental results are provided to verify the proposed topology.

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.

Pulse width modulation of three-phase switched boost inverter

This paper presents the steady state analysis of a three-phase switched boost inverter (SBI). A Pulse Width Modulation (PWM) control strategy suitable for the gate control signal generation of the three-phase SBI is also described in this paper. The proposed PWM control technique has been implemented in digital domain using Texas Instruments TMS320F28335 digital signal processor (DSP). The steady state analysis and the PWM control technique are verified using an experimental prototype of three-phase SBI supplying a balanced three-phase load. The gate control signals for the experimental prototype of SBI are generated using the DSP. A comparison of the SBI with traditional three-phase voltage source inverter (VSI) for the same input and control parameters is also given in this paper. The experimental results presented in the paper show good correlation with the theoretical analysis.

Analysis and PWM control of three-phase boost-derived hybrid converter

This paper proposes a power converter architecture which can provide a step-up dc and a three-phase ac output simultaneously from a single dc input in a single-stage conversion. This architecture, named three-phase boost-derived hybrid converter (3-φ BDHC), is derived from a conventional boost converter by replacing the control switch with a three-phase bridge network. Compared to conventional voltage source inverters, the 3-φ BDHC topology has inherent shoot-through protection capability and continuous input current. Since the boost and the inverter functions are integrated within a single architecture, the power processing density of the overall system is higher and the coordination of power flow into two different outputs becomes easier. Both the step-up dc and the three-phase ac outputs can be independently regulated. In addition to a conventional 3-φ BDHC, this paper also describes the 3-φ BDHC topology where the neutral of the three-phase filter is connected to the split-dc output capacitor. This split-dc capacitor arrangement allows for independent control of each of the three-phase voltages at unbalanced load conditions. A suitable pulse-width-modulation (PWM) control strategy for the purpose of regulation of each of the outputs (dc and ac) has been described. Experimental results have been shown to validate the converter operation, when a single dc input provides a step-up dc and a three-phase ac using a 150 W experimental prototype; the ac output is generated at fundamental frequencies of 50 Hz and 400 Hz.

Implementation and control of Switched Boost Inverer for DC nanogrid applications

Switched boost inverter (SBI) is a single stage power converter that can supply both dc and ac loads simultaneously. 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 EMI noise immunity when compared to the VSI. These features make the SBI suitable for microgrid and 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 DC nanogrid are discussed in detail. A closed loop control system is also designed for the SBI supplying both DC and AC loads using Synchronous Reference Frame (SRF) approach, and it is implemented in digital domain using Texas Instruments TMS320F28335 Digital Signal Processor (DSP). The control system of SBI has been experimentally validated using a 0.5 kW experimental prototype of SBI supplying both DC and AC loads, and the relevant experimental results are presented in the paper. The experimental results show that the DSP based control system shows excellent performance under the steady state as well as during the transients in either DC or AC loads in the system. The low cross regulation of the control system has also been verified for a 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.