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 Connected DC–DC Converters

A hardware testbed platform emulating multiple-area power system scenario dynamics has been established aiming at multiple time-scale real-time emulations. In order to mimic real power flow situations in the utility system, the load emulators have to behave like real ones in both their static and dynamic characteristics. A constant-impedance, constant-current, and constant-power (ZIP) model has been used for static load types, while a three-phase induction motor model has been built to represent dynamic load types. In this paper, ways of modeling ZIP and induction motor loads and the performance of each load emulator are discussed. Comparisons between simulation and experimental results are shown as well for the validation of the emulator behaviors. A real-time composite power load emulator is then demonstrated with desired characteristics and detailed transients for representing a power system PQ bus dynamics.

Static and Dynamic Power System Load Emulation in a Converter-Based Reconfigurable Power Grid Emulator

This paper extends the application of current-mode, shared-bus converters to power system architectures configured as Parallel-Input, Series-Output (PISO). By employing a PISO interconnect method, current-mode commercial-off-the-shelf (COTS) dc-dc converters can deliver higher output voltages, provide flexible options for power system expansion, and preserve system efficiencies equal to that obtained from standalone converters. However, without proper control, non-uniformly distributed voltages occur due to converter component mismatch. System reliability suffers as a result of thermal overstress to the converters that contribute a greater portion of the output power. Conversely, robust system stability and uniform output voltage distribution among series-connected converters is realized through output voltage distribution control. Through both computer simulation and experimental prototype, the uniform voltage distribution power converter architecture is validated and successfully applied during power converter burn-in testing whereby converter load energy is recycled to the power system input, resulting in 49% to 80% conservation of energy

Uniform Voltage Distribution Control for Paralleled-Input, Series-Output Connected Converters

In this paper, a new approach for the burn-in test of three-phase uninterruptible power supplies is proposed. This method can perform the energy recovery for reducing the test cost, while the current supplied from the utility can be steered to be more sinusoidal. When a large number of burn-in test systems are activated such that harmonic problems may become more serious, the proposed method is also suggested based on its immunity to possible harmonies infiltration coming from the tested product to the utility power supplies. This method has been tested through simulation study and hardware experiments. Test results help consolidate the feasibility of the approach for the applications considered.

https://u.dianyuan.com/bbs/u/26/1109124455.pdf

Design and operation of burn-in test system for three-phase uninterruptible power supplies

This letter presents a feasible method for electrical AC power source burn-in test. The proposed architecture consists of two power stages. It consumes a lesser amount of energy than the conventional method and provides extra flexibility for the test load. To implement the proposed idea, a simple control strategy and system design is presented in this letter. A case study for an adjustable-speed AC motor drive is demonstrated by means of a prototype experiment to prove its performance and effectiveness.

Energy recycling for electrical AC power source burn-in test

A method for load testing AC and DC power supply equipment that minimizes harmonics and allows for control of the utility input power factor is presented. This testing method produces minimal losses in the load banks by recirculating the power back to the equipment input. Two types of recirculating load banks are presented: synchronized and nonsynchronized. In synchronized load banks, power flow from the output to the input of the unit is controlled by injecting the series voltage. Circulation of power in a nonsynchronized load is achieved by processing the load power through a utility interactive inverter which is synchronized with the utility. The theory of operation of quadrature voltage injection and the results of the experiments indicating the steady-state as well as the transient performance of the load banks are given. The financial benefits of using a recirculating load bank are analyzed, and the results are presented. >

V. Rangaswamy

Papers

Load bank elimination for UPS testing