Arthur H. Chang

A systems approach to photovoltaic energy extraction

Per-panel photovoltaic energy extraction with integrated converters can increase overall array tracking efficiency. Also, switched-capacitor (SC) converters have been evaluated for many applications because of the possibility for on-chip integration; applications to solar arrays are no exception. This paper presents a comprehensive system-level look at solar installations, finding possibilities for optimization at and between all levels of operation in an array. Specifically, this paper examines new arrangements and options for applying switched-capacitor circuits at 3 levels: for the panel and sub-panel level, as part of the overall control strategy, and for ensuring stable and robust interface to the grid with the possibility of eliminating or reducing the use of electrolytic capacitors.

Capacitor-Less Photovoltaic Cell-Level Power Balancing using Diffusion Charge Redistribution

This paper presents a new strategy, diffusion charge redistribution (DCR), for balancing power among photovoltaic cells to increase energy extraction and to improve maximum power-point tracking (MPPT) efficiency under partial shading conditions. With DCR, testing and binning during cell manufacturing can be eliminated and significant cost savings can be achieved during production. The proposed technique performs power balancing by taking advantage of the intrinsic diffusion capacitance of the solar cells and requires no external passive components for energy storage, thereby minimizing power electronics cost and complexity. Strings balanced by this technique exhibit power versus current curves that are convex, which also greatly reduces the cost and complexity of the required MPPT algorithm.

Design of DC system protection

A modified Z-source breaker topology is introduced to minimize the reflected fault current drawn from a source while retaining a common return ground path. A conventional Z-source breaker does not provide steady-state overload protection and can only guard against extremely large transient faults. The Z-source breaker can be designed for considerations affecting both rate of fault current rise and absolute fault current level, analogous in some respects to a “thermal-magnetic” breaker. The proposed manual tripping mechanism enables protection against both instantaneous current surges and longer-term over-current conditions. The fault operation intervals of the proposed Z-source breaker topologies are demonstrated in SPICE simulation.

Analysis and Design of DC System Protection Using Z-Source Circuit Breaker

A modified Z-source breaker topology is introduced to minimize the reflected fault current drawn from a source while retaining a common return ground path. Conventional Z-source breaker topologies do not provide steady-state overload protection and can only guard against extremely large transient faults. The Z-source breaker can be designed for considerations affecting both rate of fault current rise and absolute fault current level, analogous in some respects to a thermal-magnetic breaker. Detailed analysis and design equations are presented to provide a framework for sizing components in the Z-source breaker topology. In addition, the proposed manual tripping mechanism enables protection against both instantaneous current surges and longer-term overcurrent conditions. The fault operation intervals of the proposed Z-source breaker topologies are both demonstrated in SPICE simulation and validated in experimental characterization.

Capacitor-less photovoltaic (PV) cell-level power balancing using diffusion charge redistribution

This paper presents a new strategy, diffusion charge redistribution (DCR), for balancing power among photovoltaic cells to increase energy extraction and to improve maximum power point tracking (MPPT) efficiency under partial shading conditions. With DCR, testing and binning during cell manufacturing can be eliminated, and significant cost savings can be achieved during production. The proposed technique performs power balancing by taking advantage the intrinsic diffusion capacitance of the solar cells and requires no external passive components for energy storage, thereby minimizing power electronics cost and complexity. Strings balanced by this technique exhibit power versus current curves that are convex, which also greatly reduces the cost and complexity of the required MPPT algorithm.

Bumpless Automatic Transfer for a Switched-Doubly-Fed-Machine Propulsion Drive

Variable-speed drives (VSDs) combined with doubly-fed machines (DFMs) offer interesting flexibility for power electronic drive design. These also provide opportunities for controlling interactions with an ac grid. Design options are most versatile for the VSD DFM when the machine stator can be operated from an ac or a dc source, selected as appropriate. This paper presents a silicon-controlled rectifier (SCR)-based transfer switch that can connect the stator of the DFM either to an ac source or a dc source “on-the-fly.” Current commutations of the SCRs and a “bumpless” transition in shaft behavior are both controlled from the rotor. Experimental results demonstrate wide-speed-range and four-quadrant operation of the drive achieved with a rotor converter rating that is one third of the DFM power rating.

Differential diffusion charge redistribution for photovoltaic cell-level power balancing

Mismatch loss remains an important issue to address in PV systems, and many power electronic solutions have been proposed to recover these losses. However, conventional power electronics for solar power optimization often have to make tradeoffs among conversion efficiency, optimization granularity, and overall system cost. This paper presents a cell-level power balancing scheme that breaks the existing design paradigm. The proposed architecture simultaneously achieves maximum power point tracking without any external passive components at the cell-level, and maintains differential power processing with zero insertion loss. This is accomplished by leveraging the recently proposed diffusion charge redistribution technique, taking advantage of the readily available diffusion capacitance of solar cells to perform power balancing rather than relying on adding costly energy storage components. Furthermore, a dual current inverter interface is introduced to avoid processing common-mode generated power in order to minimize overall conversion loss. Significant boost in overall system efficiency is achieved under both matched and partial shading conditions. Simulation results are included to demonstrate the feasibility and benefit of this approach.

Single-sided AC magnetic fields for induction heating

We present simulations and demonstrate experimentally a new concept in winding a planar induction heater. The winding results in minimal ac magnetic field below the plane of the heater, while concentrating the flux above. Ferrites and other types of magnetic shielding are typically not required. The concept of a one-sided ac field can generalized to other geometries as well.

Quad-switch push-pull (QSPP) RF amplifier with direct, simultaneous modulation of phase and pulse position for spread-spectrum power applications

We present a new RF power amplifier for spread spectrum applications, including wireless power transfer with low electromagnetic interference (EMI). The amplifier delivers half sine wave voltage pulses of either polarity through direct push-pull modulation of phase and pulse position. EMI is a concern not only from a regulatory perspective, but also in medical and other critical environments. The voltage pulses can be optimized by a variety of methods for specific spectral characteristics to create a current, and hence a high frequency magnetic field with a spread spectrum. The topology takes advantage of the inherent characteristics of GaN FET devices.

Improved transient response control strategy and design considerations for switched-capacitor (SC) energy buffer architectures

Switched-capacitor (SC) techniques have been proposed for energy buffering applications between DC and AC grids. These techniques have been implemented using film or ceramic capacitors and have been shown to achieve high energy utilization and comparable effective energy density to electrolytic capacitors. Practical applications require control schemes capable of handling transients. This paper takes a comprehensive view of the SC energy buffer design space and examines tradeoffs regarding circuit topology, switching configuration, and control complexity. A two-step control methodology that mitigates undesirable transient responses is proposed.