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Mukherjee, Satyaki

Publications and source records attributed to Mukherjee, Satyaki.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

1 kV, 10-kW SiC-Based Quadruple Active Bridge DCX Stage in a DC to Three-Phase AC Module for Medium-Voltage Grid Integration

Interfacing low voltage dc to medium voltage three-phase ac grid is often based on series-stackable modular converter architectures. To minimize energy storage requirements, it is advantageous to employ a quadruple active bridge (QAB) stage operating as a "dc transformer" in each stackable module. The QAB stage offers three isolated dc link voltages, which then allow for flexible stacking of three single-phase dc-to-ac inverter stages. Each of the module phases processes a pulsating power having a component at twice the line frequency. This presents a challenge in maintaining zero voltage switching (ZVS) on the secondary sides of the QAB during low-power portions of the line cycle. This article is focused on the design of the QAB stage. A detailed analysis of ZVS switching waveforms is presented, including effects of nonlinear device capacitances. It is shown how ZVS can be achieved at all times using a relatively small circulating current provided by the magnetizing inductance of the high-frequency transformer. Analytical expressions are given for the optimal values of the magnetizing inductance and the dead times of the QAB primary and secondary bridges. This approach is verified by experimental results on a 1 kV, 10-kW SiC-based prototype, demonstrating a relatively flat efficiency curve with a peak efficiency of 97.1% at 75% load.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2021

A High-Frequency Planar Transformer with Medium-Voltage Isolation

This paper presents the design of a low-loss, high-frequency planar transformer having medium-voltage (10’s of kV) isolation capability while transformer primary and secondary windings are interleaved to reduce losses. Medium-voltage isolation between adjacent printed circuit board (PCB) layers is extremely challenging using traditional PCB dielectrics. The isolation requirement is met using PCB with 7 kV/mil polyimide (Panasonic Felios RF775) as the dielectric, and by an appropriate layout of the windings and the inter-winding vias. The transformer is used to implement a dual active bridge (DAB) converter in a stackable dc-ac architecture where the dc port is connected to a photovoltaic (PV) string and ac outputs are connected in series to achieve direct PV string-to-medium voltage conversion without the need for low-voltage collection or a bulky line frequency transformer. Since each DAB transformer processes time-varying power, a design methodology is developed to minimize line-cycle-averaged losses. Experimental results are presented for a 1:1 planar transformer in a 7.5 kW SiC-based dc-to-ac module operating at 200 kHz. Isolation of 26 kV between the primary and secondary layers and between the windings and the core is verified using a hipot tester.

insulation resistance↗
DOE OSTI2021

A Novel Decentralized PWM Interleaving Technique for Ripple Minimization in Series-Stacked DC-DC Converters: Preprint

Cascaded dc-dc converters are commonly used in applications where distributed energy sources or loads are connected to elevated voltage levels for power transfer. In such systems, it is advantageous to minimize the ripple on the bus current and voltage by proper phase shifting of the pulse-width modulation (PWM) pulses among the converters via a method known as interleaving. Existing approaches use either a centralized controller or separate communication lines among the stacked converters to control their relative PWM switch transitions. The key drawbacks are that these methods entail significant wiring, the central controller acts as a single point of failure, and implementation on very large numbers of units is impractical. In this paper, we introduce a decentralized interleaving control (DIC) strategy that acts on local current measurements at every converter and achieves communication-free PWM interleaving among the series-stacked converters. The proposed controller is simple in structure and is shown to converge asymptotically to the interleaved state irrespective of clock drifts among the digital signal processors. Experimental results are provided for a system of five series-connected converters showing a 10 times reduction in the current ripple compared to normal operation.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2021

A High-Frequency Planar Transformer with Medium-Voltage Isolation: Preprint

This paper presents the design of a low-loss, high-frequency planar transformer having medium-voltage (10's of kV) isolation capability while transformer primary and secondary windings are interleaved to reduce losses. Medium-voltage isolation between adjacent printed circuit board (PCB) layers is extremely challenging using traditional PCB dielectrics. The isolation requirement is met using PCB with $7$\,kV/mil polyimide (Panasonic Felios RF775) as the dielectric, and by an appropriate layout of the windings and the inter-winding vias. The transformer is used to implement a dual active bridge (DAB) converter in a stackable dc-ac architecture where the dc port is connected to a photovoltaic (PV) string and ac outputs are connected in series to achieve direct PV string-to-medium voltage conversion without the need for low-voltage collection or a bulky line frequency transformer. Since each DAB transformer processes time-varying power, a design methodology is developed to minimize line-cycle-averaged losses. Experimental results are presented for a 1:1 planar transformer in a 7.5\,kW SiC-based dc-to-ac module operating at 200 kHz. Isolation of 26 kV between the primary and secondary layers and between the windings and the core is verified using a hipot tester.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2020

Decentralized Control of Cascaded H-Bridge Inverters for Medium-Voltage Grid Integration: Preprint

This paper introduces a fully decentralized control strategy that allows for individualized active and reactive power control of H-bridge inverters connected in series. After formulating a model of the system power flows, we outline a communications-free approach where each inverter can act on independent commands. Inverter-level feedback is accomplished locally via a measurement of current flowing through the stack. A key feature is the lack of any centralized control routines or phase-locked loop. In this framework, the reactive power control loops achieve voltage synchronization among the converters and the grid, and the active power control loops modulate the terminal voltage amplitudes that influence power delivery. Furthermore, pole placement via state feedback is used to ensure stability of voltage synchronization while also enabling tracking of bidirectional power commands. Simulations are presented to validate the proposed approach.

communication-free modular converter control↗
DOE OSTI2020

LCOE Design Optimization Using Genetic Algorithm with Improved Component Models for Medium-Voltage Transformerless PV Inverters

For real-world installations of photovoltaic and other renewable energy resources, the critical design metric is the levelized cost of energy (LCOE); however, many power electronics design optimizations are performed with efficiency and power density as the primary design goals. Recent work has shown that a new LCOE-focused optimization approach can yield improved system designs balancing cost and energy generation. This paper expands the LCOE optimization approach by considering comprehensive optimization parameters, adding new modeling of inductor cost, extending the semiconductor model to include effects of losses on housing cost, and implementing a genetic algorithm to improve computation efficiency.

41 EE - Solar Energy Technologies Office (EE-4S)↗