Santanu Mishra

Analysis and PWM Control of Switched Boost Inverter

The Z-source inverter (ZSI) employs an LC impedance network between the main inverter bridge and the power source. The unique feature of the ZSI is that it can operate either in buck or boost mode with a wide range of obtainable output voltages from a given input voltage. This topology also exhibits better electromagnetic-interference noise immunity when compared to a traditional voltage-source inverter (VSI). However, the LC impedance network of ZSI significantly increases the size and cost of the power converter and can make it unsuitable for low-power applications. This paper proposes a novel topology called switched boost inverter (SBI) which exhibits similar advantages of ZSI with lower number of passive components and more active components compared to ZSI. The steady-state and small-signal analyses of SBI, along with its pulsewidth modulation (PWM) control strategies, have been discussed in this paper. This paper also presents a comparison of SBI and ZSI with the same input and output parameters. The theoretical analysis given in this paper has been validated using a laboratory prototype of SBI, and the experimental results are presented for verification. The experimental harmonic spectrum of the inverters output voltage with the proposed PWM technique is also plotted and compared with that of a traditional VSI. All the experimental results show good correlation between theory and experiments.

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.

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.

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.

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 Magnetically Coupled Feedback-Clamped Optimal Bidirectional Battery Charger

This paper presents a magnetically coupled feedback-clamped optimal bidirectional battery charger. The proposed charger acts as a current source, i.e., acts in constant-current (CC) mode with a controlled output current in case of deep discharge of a battery, and as a voltage source, i.e., acts in constant-voltage (CV) mode with a controlled output voltage for near-100% battery state of charge. The proposed circuit is universal from the battery voltage point of view, i.e., can charge a battery with any given voltage rating, and adaptive from the optimum charging current requirement viewpoint, i.e., can adapt to the optimum battery charging current. The presented solution uses a magnetically coupled bidirectional converter topology. In order to make the system feedback controlled during the whole cycle of charging, the regulation loop is clamped, and hence, automatic and smooth transition from the CC to CV mode is achieved without the need of any extra switching circuit or control loop. Experimental and simulation results for a 250-W prototype are presented to verify the proposed system. The prototype shows maximum efficiencies of 90.24% under boost mode and 92.7% under buck mode of operation. The performance of the charger is verified using two different 12-V-7-Ah and 12-V-32-Ah lead-acid batteries.

Design-Oriented Analysis of Modern Active Droop-Controlled Power Supplies

Active droop control of voltage regulators and point of loads is a preferred way of implementing adaptive voltage positioning to save motherboard space. This paper develops an improved model and design methodology for this control. The conventional model is explained and need for an improved model is described. Based on this improved model, a generalized design procedure, applicable irrespective of the modulation scheme, is developed. Experimental verifications on a five-phase/120-A prototype are presented to validate the design procedure. Results show that the loop performance and output impedance predictions of the model are accurate.

Synthetic-ripple modulator for synchronous buck converter

Comprising a hysteretic comparator and a ripple synthesizer, the synthetic-ripple modulator (SRM) allows voltage-hysteretic modulation to be realized in low-voltage buck converters where the natural voltage ripple is too small for reliable hysteretic operation. Circuit implementation, steady-state operation, and design equations are described for an SRM controlling a buck dc-dc converter. The basics are verified experimentally by a buck converter switched at 420 kHz and delivering 10 A at 1.8 V.

A Wide Bandwidth Electronic Load

Electronic load (E-load) is commonly used to test power supplies. In order to test computer power supplies, the E-load must possess an ideal controlled current source property which draws a desired load current even in the case of a very low terminal voltage of the source under test (SUT). It also needs to have superior dynamic performance to simulate high-slew-rate load transients. This paper proposes the design of a switching-converter-based E-load with very large operational bandwidth. The overall architecture of the E-load consists of a low-bandwidth converter, which functions under steady state, and a high-bandwidth auxiliary circuit that is only active during transient state. The converter circuit is realized using a novel switched-boost topology, and the auxiliary circuit is realized using a MOSFET operating at the edge of saturation and linear region. The proposed topology is capable of sinking a specific amount of load current even with a very low SUT terminal voltage. Simulation and experimental validations are provided to verify the proposed concepts. A prototype has been built to test the proposed architecture. The operational input voltage (SUT voltage) ranges of the prototype are between 0.5 and 6 V. The load current range is between 0.75 and 7 A. The results validate the excellent dynamic characteristics of the proposed architecture.

Dynamic Characterization of the Synthetic Ripple Modulator in a Tightly Regulated Distributed Power Application

Hysteretic modulators have superior dynamic performance, and they also help reduce the number of output capacitors without sacrificing the transient response. For proper hysteretic operation, the voltage ripple is required to be piecewise linear and noise free. With modern computational integrated circuits lower supply voltage with tight regulation requirements, the output voltage ripple is both small and noisy. The synthetic ripple modulator (SRM) allows proper hysteretic operation even with a small and corrupted output voltage ripple. This paper discusses the dynamic behavior of the SRM. Small-signal characteristics of the modulator are derived. An easy-to-use numerically efficient model has been developed to accurately predict the small- and large-signal behavior of the converter driven by the SRM. The model is able to predict the small-signal behavior of the SRM up to half the switching frequency with sufficient accuracy. It can predict the same large-signal responses as real-time simulation, but at two orders of magnitude less in computation time. Laboratory tests on a 1.8 V/20 A single-phase prototype shows good correlation between experimental results and theoretical predictions both in frequency and time domain.