Michael Willhoff

Uniform Voltage Distribution Control for Series Connected DC–DC Converters

This paper investigates applications of current-mode, shared-bus commercial-off-the-shelf (COTS) dc-dc converters to power system architectures configured as parallel-input, series-output (PISO) and series-input, parallel-output (SIPO). By employing a PISO (or SIPO) architecture, current-mode COTS converters can transform their system input voltage to higher (or lower) system output voltage, provide ease and flexibility of power expansion, and preserve system efficiencies equal to those of standalone converters. Nonuniform output (or input) voltages still exist within a PISO (or SIPO) power system using identical converters when the system lacks proper distribution control of the series connected output (or input) voltages-and thus, system reliability suffers from thermal overstress to the converters that contribute a greater portion of the output power. Through unified approaches of voltage distribution control for the PISO and SIPO architectures, a series-connected converter power system attains robust stability and reliability. Two effective approaches to uniform voltage distribution control-the central-limit and maximum-limit voltage distribution-will be discussed. Both computer simulation and experimental prototypes validate both of the uniform voltage distribution power converter architectures.

Uniform voltage distribution control for series-input parallel-output, connected converters

This paper extends the application of current-mode, shared-bus converters to power system architectures configured as series-input, parallel-output (SIPO). By employing a SIPO interconnect method, current-mode commercial-off-the-shelf (COTS) dc-dc converters can transform higher input voltages into low output voltages, provide flexible options for power system expansion, and preserve system efficiencies equal to that obtained from standalone converters. However, without proper control, converter internal component mismatch cause the input voltage to be non-uniformly distributed. System reliability suffers as a result of thermal overstress to the converters that contribute a greater portion of the input power. Conversely, robust system stability and uniform input voltage distribution among series-connected converters is realized through input voltage distribution control. Through computer simulation and experimental prototype the uniform voltage distribution power converter architecture is validated and successfully applied

Current-Sharing/Voltage-Distribution Control for Interconnected DC-DC Converters

This paper presents advanced interconnection and control approaches for three currentmode, shared-bus converter architectures: (1) parallel-input parallel-output (PIPO), (2) parallelinput series-output (PISO), and (3) series-input parallel-output (SIPO). Without proper control, nonuniform current sharing or voltage distribution may exist among interconnected DC-DC converters, negatively impacting reliability. Using the control schemes presented herein, reliable and robust power system performance is achievable from the series and/or parallel interconnection of commercial-off-the-shelf (COTS) DC-DC converters. In particular, PIPO connected COTS converters have been well-known and already achieved uniform current-sharing by using the provided parallel control port as a common “shared bus” for commanding the parallel-connected converters to operate as voltage-controlled current sources. This paper presents two control alternatives for PIPO converter systems based on the “shared-bus” approach: (1) minimum-voltageerror shared-bus and (2) maximum-voltage-error shared-bus. Furthermore, the current-mode shared-bus converters extend their applications to power system architectures configured as PISO and SIPO. Employing a PISO (or SIPO) interconnect method, current-mode COTS converters can transform their system input voltages to higher (or lower) system output voltages, provide flexibility for power system expansion, and preserve system efficiencies equal to that obtained from stand-alone converters. The system achieves robust stability and uniform voltage sharing among series-connected converters through unique output and input voltage distribution control approaches for the PISO and SIPO power architectures. Two effective approaches to uniform voltage distribution control, the central-limit (CL) and maximum-limit (ML) distribution, will be discussed. Both computer simulation and experimental prototypes validate both series-connected power converter architectures with the two control approaches.

Optimum power tracking among series-connected power sources with uniform voltage distribution

This paper presents a power system architecture where series-input parallel-output (SIPO) converters are controlled to achieve uniform input voltages across their respective series-connected power sources while also tracking the system optimum power point; the system optimum power point is the maximum power drawn from the series-connected power sources while their voltages are kept uniformly distributed.12 With proper uniform input voltage distribution control, near maximum use of the power sources is achieved by employing only one maximum power tracking (MPT) controller instead of multiple MPT controllers dedicated for their respective power sources. Provided that the maximum power point voltages of the input power sources are similar, the resulting system architecture offers near-maximum power transfer with lower parts count. A feasibility study using computer simulation has successfully validated two SIPO power architectures and their control concepts for optimum power transfer.

Optimum energy harvesting among distributed power sources with uniform voltage distribution

This paper presents two power system architectures where distributed-input parallel-output (DIPO) DC-DC converters are controlled to achieve their equal input voltages while harvesting electricity from their distributed power sources at a system optimum power point; the system optimum power point is the maximum power drawn from the distributed power sources while their voltages are kept uniformly distributed1 2 even though their individual peak powers are different. With proper uniform input voltage distribution control, near maximum use of the power sources is achieved by employing only one maximum power tracking (MPT) controller instead of multiple MPT controllers dedicated for their respective power sources. Provided that the maximum power point voltages of the input power sources are similar, the resulting system and control architectures offer near-maximum power transfer with a lower parts count. The two DIPO power converter architectures are also described in detail: one with the battery-dominated output voltage bus and the other with the regulated output voltage bus. A feasibility study using computer simulation has successfully validated both power architectures and their control concepts for optimum energy harvesting and maximal fault-tolerances for failures of more than one power source or converter.

High-voltage-input, low-voltage-output, series-connected converters with uniform voltage distribution

This paper presents a power system consisting of current-mode, shared-bus converters configured as Series-Input, Parallel-Output (SIPO). These current-mode commercial-off-the-shelf (COTS) dc-dc converters transform a 1kV system input voltage into a 5V output with up to 500 Watts of power. The SIPO power system provides for system expansion and preserves the standalone converters efficiency of over 80%. Uniform input voltage distribution control improves power system reliability by distributing thermal stresses equally among the series-connected converters. Furthermore, robust system stability and uniform input voltage distribution among series-connected converters is realized without control conflict. A computer simulation and an experimental 1 kV 500 W prototype were successfully implemented to validate the uniform voltage distribution power converter architecture.

Independently-Sourced Series-Input Connected Converters with Uniform Current-Sharing

This paper extends the application of current-mode, shared-bus converters to independently-sourced power system architectures consisting of multiple power- processing channels, each of which is configured as series-input, parallel-output (SIPO). By employing a SIPO interconnect method, current-mode commercial-off-the- shelf (COTS) DC-DC converters can transform higher input voltages into low output voltages, provide flexible options for power system expansion, and preserve system efficiencies equal to those obtained from standalone converters. Robust system stability and uniform input voltage distribution among series-connected converters is realized through input voltage distribution control. Active current-sharing control ensures nearly uniform distribution of the channel-output currents between the independently sourced SIPO power channels. Through computer simulation and experimental prototypes the uniform voltage distribution power converter architecture with current-sharing is validated and successfully applied.

Current-sharing among parallel-connected systems of active power factor correction

This paper presents active current-sharing control approaches for parallel-connected AC-to-DC power system architectures consisting of multiple power-processing channels, each of which comprises a cascade connection of a front-end active power factor correction (APFC) stage and an isolated back-end DC-DC converter. 12By employing a current-sharing method to the back-end converters, current-mode commercial-off-the-shelf (COTS) DC-DC converters can provide uniform current-sharing among all power-processing channels while retaining stiff system output voltage regulation without control conflicts among output voltage regulators distributed in the converters. This results in uniform power-sharing among the front-end APFC stages that are connected to either a common AC power source or independent AC power sources that may possess different frequencies of operation (i.e. 50 Hz versus 60 Hz). Through computer simulation and an experimental prototype, current-sharing control for the parallel-connected APFC architectures is validated and successfully applied.

Optimum energy harvesting for series-connected power sources with uniform voltage distribution

Presented herein are three possible maximum power tracking approaches of harvesting energy from series-connected power sources: (1) commonly drawing the same current without active control for uniform voltage distribution among the output voltages of individual power sources, (2) partially across all individual power sources while being series-connected with uniform voltage distribution (UVD) control of their sourcing voltages, and (3) directly across individual power sources of which their peak-power voltages are independently tracked and controlled using their own independent maximum power tracking (IMPT) controllers. The energy harvesting approach (1) delivers far from optimum power, particularly when these sources are usually not identical. While the IMPT approach (3) enables the ideal peak power to be obtainable, the energy harvesting approach (2) still provides near optimum power with less control complexity that preserves fault-tolerance. This paper presents two power system architectures, each consisting of series-connected power sources and series-input parallel-output (SIPO) converters that are controlled to achieve their uniform input voltages across their respective sources while also tracking the system optimum power point being sufficiently close to the ideal system peak power. Feasible study through computer simulation successfully validates the SIPO power architecture and control concept developed for optimum power transfer.

Uniform Voltage Distribution Control for Series Connected DC-DC Converters

This paper investigates applications of current-mode, shared-bus commercial-off-the-shelf (COTS) dc-dc converters to power system architectures configured as parallel-input, series-output (PISO) and series-input, parallel-output (SIPO). By employing a PISO (or SIPO) architecture, current-mode COTS converters can transform their system input voltage to higher (or lower) system output voltage, provide ease and flexibility of power expansion, and preserve system efficiencies equal to those of standalone converters. Nonuniform output (or input) voltages still exist within a PISO (or SIPO) power system using identical converters when the system lacks proper distribution control of the series connected output (or input) voltages-and thus, system reliability suffers from thermal overstress to the converters that contribute a greater portion of the output power. Through unified approaches of voltage distribution control for the PISO and SIPO architectures, a series-connected converter power system attains robust stability and reliability. Two effective approaches to uniform voltage distribution control-the central-limit and maximum-limit voltage distribution-will be discussed. Both computer simulation and experimental prototypes validate both of the uniform voltage distribution power converter architectures.